From: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Saturday, October 20, 2012 8:18 PM
Subject: [Electric Boats] Digest Number 3247
15 New Messages
Digest #3247
Messages
Sat Oct 20, 2012 11:37 am (PDT) . Posted by:
"Myles Twete" electric_barge_boat
The answer: It depends.
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
-Myles Twete, Portland
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
_____
From: Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
_____
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
_____
From: John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
"Neurosurgery for computer looms."
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
-Myles Twete, Portland
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
_____
From: Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
_____
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
_____
From: John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
"Neurosurgery for computer looms."
Sat Oct 20, 2012 12:04 pm (PDT) . Posted by:
"ChristopherH" clh5_98
Thanks for all the great responses on my question. Myles' explanation is clear that paralleling strings will increase range. This I understand. My original question is around the concept of what I think is called "buddy pairing". I believe this is different than just paralleling the 2 strings. This parallels 2X6 volt batteries and then places them in series with subsequent pairs of 6 volt batteries until you reach 48 volts. Does anyone have any insight into if there is any difference between this and the standard configuration of just placing two series strings in parallel?
Chris
--- In electricboats@ yahoogroups. com, "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries youâre using and the 2 battery stringsâ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105âs (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon Johnâs Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way: Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
> _____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
Chris
--- In electricboats@ yahoogroups. com, "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries youâre using and the 2 battery stringsâ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105âs (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon Johnâs Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way: Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
> _____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
Sat Oct 20, 2012 12:21 pm (PDT) . Posted by:
"Myles Twete" electric_barge_boat
As I understand it, by buddying up at 6v, 12v, or half-pack intervals, you benefit by reducing the chance that a battery will go under-voltage.
So say you have 1 weak cell in 1 battery and after running for awhile, that battery is pulled to its knees and is at 5.2v yet you are still drawing 50amps from that string. That battery is about to be damaged. Paralleling the string doesn't help the battery. If instead there is connectivity between 2 buddies, then that 50-amps that is flowing will flow around the weak battery and the weak battery won't be hurt. There's little guarantee of saving that battery if you're only paralleling at the string level. There are also benefits in charging. A weak battery will reach a high voltage before the others. When that happens, 2 things are bad: First, the cell really shouldn't be charged much more (unless it needs equalization anyway), and second, the string will reach its charge target before the rest of the cells get charged. By buddying the batteries up, this won't happen.
I'm sure there are better explanations online somewhere…
-MT
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of ChristopherH
Sent: Saturday, October 20, 2012 12:04 PM
To: electricboats@ yahoogroups. com
Subject: [Electric Boats] Re:Battery Buddy Pairing
Thanks for all the great responses on my question. Myles' explanation is clear that paralleling strings will increase range. This I understand. My original question is around the concept of what I think is called "buddy pairing". I believe this is different than just paralleling the 2 strings. This parallels 2X6 volt batteries and then places them in series with subsequent pairs of 6 volt batteries until you reach 48 volts. Does anyone have any insight into if there is any difference between this and the standard configuration of just placing two series strings in parallel?
Chris
--- In electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> , "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you’re using and the 2 battery strings’ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105’s (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon John’s Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> [mailto:electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> ] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com>
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way: Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> " <electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> >
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> " <electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> >
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
> _____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com>
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
So say you have 1 weak cell in 1 battery and after running for awhile, that battery is pulled to its knees and is at 5.2v yet you are still drawing 50amps from that string. That battery is about to be damaged. Paralleling the string doesn't help the battery. If instead there is connectivity between 2 buddies, then that 50-amps that is flowing will flow around the weak battery and the weak battery won't be hurt. There's little guarantee of saving that battery if you're only paralleling at the string level. There are also benefits in charging. A weak battery will reach a high voltage before the others. When that happens, 2 things are bad: First, the cell really shouldn't be charged much more (unless it needs equalization anyway), and second, the string will reach its charge target before the rest of the cells get charged. By buddying the batteries up, this won't happen.
I'm sure there are better explanations online somewhere…
-MT
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of ChristopherH
Sent: Saturday, October 20, 2012 12:04 PM
To: electricboats@ yahoogroups. com
Subject: [Electric Boats] Re:Battery Buddy Pairing
Thanks for all the great responses on my question. Myles' explanation is clear that paralleling strings will increase range. This I understand. My original question is around the concept of what I think is called "buddy pairing". I believe this is different than just paralleling the 2 strings. This parallels 2X6 volt batteries and then places them in series with subsequent pairs of 6 volt batteries until you reach 48 volts. Does anyone have any insight into if there is any difference between this and the standard configuration of just placing two series strings in parallel?
Chris
--- In electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> , "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you’re using and the 2 battery strings’ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105’s (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon John’s Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> [mailto:electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> ] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com>
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way: Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> " <electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> >
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> " <electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com> >
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
> _____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com <mailto:electricboa ts%40yahoogroups .com>
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
Sat Oct 20, 2012 1:20 pm (PDT) . Posted by:
"oak" oak_box
So if you "buddy" the batteries, you better have fuses all over the place to keep a bad cell from dead shorting it's buddy, right? I'm guessing you should at minimum have a fuse between every buddy pair?
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 2:21 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
As I understand it, by buddying up at 6v, 12v, or half-pack intervals, you benefit by reducing the chance that a battery will go under-voltage.
So say you have 1 weak cell in 1 battery and after running for awhile, that battery is pulled to its knees and is at 5.2v yet you are still drawing 50amps from that string. That battery is about to be damaged. Paralleling the string doesn't help the battery. If instead there is connectivity between 2 buddies, then that 50-amps that is flowing will flow around the weak battery and the weak battery won't be hurt. There's little guarantee of saving that battery if you're only paralleling at the string level. There are also benefits in charging. A weak battery will reach a high voltage before the others. When that happens, 2 things are bad: First, the cell really shouldn't be charged much more (unless it needs equalization anyway), and second, the string will reach its charge target before the rest of the cells get charged. By buddying the batteries up, this won't happen.
I'm sure there are better explanations online somewhere…
-MT
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of ChristopherH
Sent: Saturday, October 20, 2012 12:04 PM
To: electricboats@ yahoogroups. com
Subject: [Electric Boats] Re:Battery Buddy Pairing
Thanks for all the great responses on my question. Myles' explanation is clear that paralleling strings will increase range. This I understand. My original question is around the concept of what I think is called "buddy pairing". I believe this is different than just paralleling the 2 strings. This parallels 2X6 volt batteries and then places them in series with subsequent pairs of 6 volt batteries until you reach 48 volts. Does anyone have any insight into if there is any difference between this and the standard configuration of just placing two series strings in parallel?
Chris
--- In electricboats@ yahoogroups. com, "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you’re using and the 2 battery strings’ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105’s (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon John’s Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way: Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
> _____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 2:21 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
As I understand it, by buddying up at 6v, 12v, or half-pack intervals, you benefit by reducing the chance that a battery will go under-voltage.
So say you have 1 weak cell in 1 battery and after running for awhile, that battery is pulled to its knees and is at 5.2v yet you are still drawing 50amps from that string. That battery is about to be damaged. Paralleling the string doesn't help the battery. If instead there is connectivity between 2 buddies, then that 50-amps that is flowing will flow around the weak battery and the weak battery won't be hurt. There's little guarantee of saving that battery if you're only paralleling at the string level. There are also benefits in charging. A weak battery will reach a high voltage before the others. When that happens, 2 things are bad: First, the cell really shouldn't be charged much more (unless it needs equalization anyway), and second, the string will reach its charge target before the rest of the cells get charged. By buddying the batteries up, this won't happen.
I'm sure there are better explanations online somewhere…
-MT
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of ChristopherH
Sent: Saturday, October 20, 2012 12:04 PM
To: electricboats@ yahoogroups. com
Subject: [Electric Boats] Re:Battery Buddy Pairing
Thanks for all the great responses on my question. Myles' explanation is clear that paralleling strings will increase range. This I understand. My original question is around the concept of what I think is called "buddy pairing". I believe this is different than just paralleling the 2 strings. This parallels 2X6 volt batteries and then places them in series with subsequent pairs of 6 volt batteries until you reach 48 volts. Does anyone have any insight into if there is any difference between this and the standard configuration of just placing two series strings in parallel?
Chris
--- In electricboats@ yahoogroups. com, "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you’re using and the 2 battery strings’ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105’s (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon John’s Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way: Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
> _____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
Sat Oct 20, 2012 1:28 pm (PDT) . Posted by:
"oak" oak_box
OK, this makes a little more sense. By paralleling the batteries instead of running them in series, you're reducing the current drawn from the battery under load. Batteries seem to have a longer life when discharged at a slower rate - so you get a longer battery life by draining the batteries more slowly. Right?
Long term, that might be the right thing to do.
Short term (while I'm more likely to run myself dry), I'd probably leave them as two separate strings till I have more data on how far I can go on how much power.
I agree that running a little slower is probably a good thing to do. And motor-sailing definitely seems to be a good way to go.
Thanks for the response!
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:37 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
The answer: It depends.
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/Peukert_ calculations. xls
-Myles Twete, Portland
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
____________ _________ _________ __
From:Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
____________ _________ _________ __
From:oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
____________ _________ _________ __
From:John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com
"Neurosurgery for computer looms."
Long term, that might be the right thing to do.
Short term (while I'm more likely to run myself dry), I'd probably leave them as two separate strings till I have more data on how far I can go on how much power.
I agree that running a little slower is probably a good thing to do. And motor-sailing definitely seems to be a good way to go.
Thanks for the response!
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:37 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
The answer: It depends.
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/Peukert_ calculations. xls
-Myles Twete, Portland
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
____________ _________ _________ __
From:Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
____________ _________ _________ __
From:oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
____________ _________ _________ __
From:John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com
"Neurosurgery for computer looms."
Sat Oct 20, 2012 1:55 pm (PDT) . Posted by:
"Kirk McLoren" kirkmcloren
automotive systems monitor each cell.
Will Rogers quote: "Stupidity got us into this – why can't it get us out?"
____________ _________ _________ __
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Saturday, October 20, 2012 1:20 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
So if you "buddy" the batteries, you better have fuses all over the place to keep a bad cell from dead shorting it's buddy, right? I'm guessing you should at minimum have a fuse between every buddy pair?
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 2:21 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
As I understand it, by buddying up at 6v, 12v, or half-pack intervals, you benefit by reducing the chance that a battery will go under-voltage.
So say you have 1 weak cell in 1 battery and after running for awhile, that battery is pulled to its knees and is at 5.2v yet you are still drawing 50amps from that string. That battery is about to be damaged. Paralleling the string doesn't help the battery. If instead there is connectivity between 2 buddies, then that 50-amps that is flowing will flow around the weak battery and the weak battery won't be hurt. There's little guarantee of saving that battery if you're only paralleling at the string level. There are also benefits in charging. A weak battery will reach a high voltage before the others. When that happens, 2 things are bad: First, the cell really shouldn't be charged much more (unless it needs equalization anyway), and second, the string will reach its charge target before the rest of the cells get charged. By buddying the batteries up, this won't happen.
I'm sure there are better explanations online somewhere…
-MT
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of ChristopherH
Sent: Saturday, October 20, 2012 12:04 PM
To: electricboats@ yahoogroups. com
Subject: [Electric Boats] Re:Battery Buddy Pairing
Thanks for all the great responses on my question. Myles' explanation is clear that paralleling strings will increase range. This I understand. My original question is around the concept of what I think is called "buddy pairing". I believe this is different than just paralleling the 2 strings. This parallels 2X6 volt batteries and then places them in series with subsequent pairs of 6 volt batteries until you reach 48 volts. Does anyone have any insight into if there is any difference between this and the standard configuration of just placing two series strings in parallel?
Chris
--- In electricboats@ yahoogroups. com, "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you’re using and the 2 battery strings’ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105’s (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down
by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon John’s Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way:
Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when
sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them
together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
>
_____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if
you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10
years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
Will Rogers quote: "Stupidity got us into this – why can't it get us out?"
____________ _________ _________ __
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Saturday, October 20, 2012 1:20 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
So if you "buddy" the batteries, you better have fuses all over the place to keep a bad cell from dead shorting it's buddy, right? I'm guessing you should at minimum have a fuse between every buddy pair?
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 2:21 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
As I understand it, by buddying up at 6v, 12v, or half-pack intervals, you benefit by reducing the chance that a battery will go under-voltage.
So say you have 1 weak cell in 1 battery and after running for awhile, that battery is pulled to its knees and is at 5.2v yet you are still drawing 50amps from that string. That battery is about to be damaged. Paralleling the string doesn't help the battery. If instead there is connectivity between 2 buddies, then that 50-amps that is flowing will flow around the weak battery and the weak battery won't be hurt. There's little guarantee of saving that battery if you're only paralleling at the string level. There are also benefits in charging. A weak battery will reach a high voltage before the others. When that happens, 2 things are bad: First, the cell really shouldn't be charged much more (unless it needs equalization anyway), and second, the string will reach its charge target before the rest of the cells get charged. By buddying the batteries up, this won't happen.
I'm sure there are better explanations online somewhere…
-MT
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of ChristopherH
Sent: Saturday, October 20, 2012 12:04 PM
To: electricboats@ yahoogroups. com
Subject: [Electric Boats] Re:Battery Buddy Pairing
Thanks for all the great responses on my question. Myles' explanation is clear that paralleling strings will increase range. This I understand. My original question is around the concept of what I think is called "buddy pairing". I believe this is different than just paralleling the 2 strings. This parallels 2X6 volt batteries and then places them in series with subsequent pairs of 6 volt batteries until you reach 48 volts. Does anyone have any insight into if there is any difference between this and the standard configuration of just placing two series strings in parallel?
Chris
--- In electricboats@ yahoogroups. com, "Myles Twete" <matwete@... > wrote:
>
> The answer: It depends.
>
>
>
> It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you’re using and the 2 battery strings’ capacities.
>
> Say you expect to draw 75amps of current while cruising and have 2 strings of T105’s (Peukert coefficient: 1.240).
>
> In one test, you charge the 2 strings up, then run with one string, then the other.
>
> In the second test, you parallel the strings, charge them up, then run with the parallel combination.
>
> In each case, you cruise at 75amps.
>
> How far can you go with each?
>
> A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
>
> For 80%DOD, the discharge time: 1.53 hours
>
> For 60%: 1.15 hours
>
> Multiplying by 2 strings: 2.3 to 3.0 hours
>
>
>
> In the second case, each string will be delivering 37.5amps.
>
> For 80%DOD, discharge time: 3.61 hours
>
> For 60%: 2.71 hours
>
> Net: 2.71 to 3.61 hours
>
>
>
> Difference: 17.8 to 20.3%
>
> Academic: 2%
>
> Real Diff: 20%
>
>
>
> I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
>
> OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down
by 0.1knot and probably make up the difference.
>
> In that case, the difference would be academic.
>
>
>
> Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
>
>
>
> See Neon John’s Peukert calculator XLS file to play with the numbers yourself:
>
> www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
>
> -Myles Twete, Portland
>
>
>
>
>
> From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
> Sent: Friday, October 19, 2012 4:11 PM
> To: electricboats@ yahoogroups. com
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Ok, I'll bite:
>
>
>
> Are we talking about a "academic difference" (2%), or a REAL difference (20%?
>
>
>
> I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
>
> But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
>
>
>
> I guess to ask a different way:
Would I really notice a difference?
>
>
>
> _____
>
> From: Arby bernt <arbybernt@. ..>
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 1:59 PM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
>
> A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
>
> We have measured more power out of the combined strings then the individual strings when
sequentially drained.
>
> Chances are a member would be willing to work it out as a proof...
>
>
>
> Arby
>
>
>
> _____
>
> From: oak <oak_box@... >
> To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
> Sent: Friday, October 19, 2012 11:22 AM
> Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Hmmm... I know I'm just an odd duck, but....
>
>
>
> It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them
together.
>
>
>
> I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
>
>
>
> It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
>
>
>
> I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
>
>
>
> Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
>
>
>
> John
>
>
>
>
_____
>
> From: John Acord <jcacord@... >
> To: electricboats@ yahoogroups. com
> Sent: Friday, October 19, 2012 12:38 PM
> Subject: [Electric Boats] Re:Battery Buddy Pairing
>
>
>
>
>
> Chris,
>
> I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
>
> So if
you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
>
> I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10
years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
>
> Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
>
> You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
>
> John
>
> Flatwater Electronics
> www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
> "Neurosurgery for computer looms."
>
Sat Oct 20, 2012 1:57 pm (PDT) . Posted by:
"Kirk McLoren" kirkmcloren
the poor DOD for lead-acid precludes it from my criteria. I want a cell I can run flat and wait a week to recharge without penalty.
Will Rogers quote: "Stupidity got us into this – why can't it get us out?"
____________ _________ _________ __
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Saturday, October 20, 2012 1:28 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
OK, this makes a little more sense. By paralleling the batteries instead of running them in series, you're reducing the current drawn from the battery under load. Batteries seem to have a longer life when discharged at a slower rate - so you get a longer battery life by draining the batteries more slowly. Right?
Long term, that might be the right thing to do.
Short term (while I'm more likely to run myself dry), I'd probably leave them as two separate strings till I have more data on how far I can go on how much power.
I agree that running a little slower is probably a good thing to do. And motor-sailing definitely seems to be a good way to go.
Thanks for the response!
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:37 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
The answer: It depends.
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/Peukert_ calculations. xls
-Myles Twete, Portland
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
____________ _________ _________ __
From:Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
____________ _________ _________ __
From:oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
____________ _________ _________ __
From:John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when
you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries
are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com
"Neurosurgery for computer looms."
Will Rogers quote: "Stupidity got us into this – why can't it get us out?"
____________ _________ _________ __
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Saturday, October 20, 2012 1:28 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
OK, this makes a little more sense. By paralleling the batteries instead of running them in series, you're reducing the current drawn from the battery under load. Batteries seem to have a longer life when discharged at a slower rate - so you get a longer battery life by draining the batteries more slowly. Right?
Long term, that might be the right thing to do.
Short term (while I'm more likely to run myself dry), I'd probably leave them as two separate strings till I have more data on how far I can go on how much power.
I agree that running a little slower is probably a good thing to do. And motor-sailing definitely seems to be a good way to go.
Thanks for the response!
____________ _________ _________ __
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:37 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
The answer: It depends.
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/Peukert_ calculations. xls
-Myles Twete, Portland
From:electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
____________ _________ _________ __
From:Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
____________ _________ _________ __
From:oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
____________ _________ _________ __
From:John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when
you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries
are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com
"Neurosurgery for computer looms."
Sat Oct 20, 2012 2:43 pm (PDT) . Posted by:
"Myles Twete" electric_barge_boat
Just to be clear, the benefit isn't just longer life. In fact, that's more intangible and as you say, long term than the real daily benefit: You would get 18-20% more range in the scenario I described. In your words, that's a "REAL difference". So if you care about the short term, this suggests paralleling the strings. I ran my boat with 2 strings of 6 T-105 batteries for several years with absolutely no issues. I currently run with just 1 string, but wouldn't for an instant consider 2 separate strings of high-Peukert batteries. The perceived benefit of having a spare string is really not that useful if you are aware of the state of your pack and plan your trips well.
-Myles
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Saturday, October 20, 2012 1:28 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
OK, this makes a little more sense. By paralleling the batteries instead of running them in series, you're reducing the current drawn from the battery under load. Batteries seem to have a longer life when discharged at a slower rate - so you get a longer battery life by draining the batteries more slowly. Right?
Long term, that might be the right thing to do.
Short term (while I'm more likely to run myself dry), I'd probably leave them as two separate strings till I have more data on how far I can go on how much power.
I agree that running a little slower is probably a good thing to do. And motor-sailing definitely seems to be a good way to go.
Thanks for the response!
_____
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:37 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
The answer: It depends.
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
-Myles Twete, Portland
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
_____
From: Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
_____
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
_____
From: John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
"Neurosurgery for computer looms."
-Myles
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Saturday, October 20, 2012 1:28 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
OK, this makes a little more sense. By paralleling the batteries instead of running them in series, you're reducing the current drawn from the battery under load. Batteries seem to have a longer life when discharged at a slower rate - so you get a longer battery life by draining the batteries more slowly. Right?
Long term, that might be the right thing to do.
Short term (while I'm more likely to run myself dry), I'd probably leave them as two separate strings till I have more data on how far I can go on how much power.
I agree that running a little slower is probably a good thing to do. And motor-sailing definitely seems to be a good way to go.
Thanks for the response!
_____
From: Myles Twete <matwete@comcast. net>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:37 PM
Subject: RE: [Electric Boats] Re:Battery Buddy Pairing
The answer: It depends.
It depends on the cruising current you expect to draw, the Peukert coefficient for the batteries you're using and the 2 battery strings' capacities.
Say you expect to draw 75amps of current while cruising and have 2 strings of T105's (Peukert coefficient: 1.240).
In one test, you charge the 2 strings up, then run with one string, then the other.
In the second test, you parallel the strings, charge them up, then run with the parallel combination.
In each case, you cruise at 75amps.
How far can you go with each?
A T105 is rated for 2 hours at 75amps --- i.e. 150amp-hours.
For 80%DOD, the discharge time: 1.53 hours
For 60%: 1.15 hours
Multiplying by 2 strings: 2.3 to 3.0 hours
In the second case, each string will be delivering 37.5amps.
For 80%DOD, discharge time: 3.61 hours
For 60%: 2.71 hours
Net: 2.71 to 3.61 hours
Difference: 17.8 to 20.3%
Academic: 2%
Real Diff: 20%
I would suggest that the difference is so close to your definition of REAL that it should make you think twice about separating the strings.
OTOH, how important is an extra 0.4 to 0.6 hours of cruising when you could slow the boat down by 0.1knot and probably make up the difference.
In that case, the difference would be academic.
Another thing to consider however is that battery life will be much greater for the case where discharge rates are 37.5amps instead of 75amps.
See Neon John's Peukert calculator XLS file to play with the numbers yourself:
www.neon-john. com/EV/ <http://www.neon- john.com/ EV/Peukert_ calculations. xls> Peukert_calculation s.xls
-Myles Twete, Portland
From: electricboats@ yahoogroups. com [mailto:electricboats@ yahoogroups. com] On Behalf Of oak
Sent: Friday, October 19, 2012 4:11 PM
To: electricboats@ yahoogroups. com
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Ok, I'll bite:
Are we talking about a "academic difference" (2%), or a REAL difference (20%?
I can believe that someone could work out a proof that there is a lower internal resistance, and therefore improved output.
But I would have to question if the "improvement" is so small that it would get lost in the noise of all the other imperfect variables on my real world boat.
I guess to ask a different way: Would I really notice a difference?
_____
From: Arby bernt <arbybernt@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 1:59 PM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Paralleled batteries will deliver more power as a result of a decreased Peukert's Effect.
A Rawson 30 we've repowered has two strings, 48v @ 100Ah, and 48v @ 170Ah (NSB100's and NSB170's).
We have measured more power out of the combined strings then the individual strings when sequentially drained.
Chances are a member would be willing to work it out as a proof...
Arby
_____
From: oak <oak_box@yahoo. com>
To: "electricboats@ yahoogroups. com" <electricboats@ yahoogroups. com>
Sent: Friday, October 19, 2012 11:22 AM
Subject: Re: [Electric Boats] Re:Battery Buddy Pairing
Hmmm... I know I'm just an odd duck, but....
It seems to me that I would MUCH rather have two separate banks, and have a switch for each bank, rather than putting them together.
I don't have much experience in electric boating, but I'm suspicious that I might be putting along, forget what I'm doing, or not paying attention when a well meaning friend has turned up the juice, or for whatever reason run my batteries down.
It would be really nice to be able to flip the switch over to the other bank, and still be able to get home.
I realize that out of "convenience" , it might be nicer to have them tied together and just have a really large capacity to begin with, and never have to flip the switch. But given the choice, I think I'd rather KNOW when I've hit my limit, than be wondering.
Is battery life generally so long that I really don't have to worry about this? (if so, I don't have nearly enough batteries... .)
John
_____
From: John Acord <jcacord@gmail. com>
To: electricboats@ yahoogroups. com
Sent: Friday, October 19, 2012 12:38 PM
Subject: [Electric Boats] Re:Battery Buddy Pairing
Chris,
I would be interested in the reason for paralleling each pair in the string. No two batteries have exactly equal chemical/electrical characteristics, so there will be slightly different sourcing/acceptance of currents. You want the battery stack to source/accept current so that each battery shares the "load" as equally as it can. By paralleling each pair you woll be forcing each pair to the terminal voltage of the other, where when you make a series string each battery can attain the voltage per it's charge state.
So if you make up a series string for the voltage you want, then parallel another string of the same voltage/capacity then differences between the two strings will be the overall terminal voltage and each battery in the string will charge/discharge according to it's individual terminal voltage and not to the terminal voltage of it's pair. With equal size/condition batteries the terminal voltage of the composite stack will be the source voltage but each individual battery will balance to it's own characteristic.
I have been running a house bank in a sailboat for many years that consists of a pair of 6v batteries wired in series for 12v, paralleled with another of the same. There will be usually about 10mv or less difference between the terminal voltage of each 6v battery pair, independent of charge state, which to me suggests that the batteries are sharing the load according to their internal resistance. As the batteries age (I get about 10 years out of a stack of flooded cell golf cart type) they seem to have the same characteristics except that the capacity is diminished over time.
Note that when combining batteries in series/parallel strings it is important that they be all the same age and condition.
You can probably convince yourself by drawing a comparable circuit of series parallel resistors, applying a voltage to the string then calculating the current in each resistor (Kirchoff's law) . Make small differences in the resistor values. Then draw it as two resistor strings paralleled and see what the difference is.
John
Flatwater Electronics
www.flatwaterfarm. com <http://www.flatwate rfarm.com/>
"Neurosurgery for computer looms."
Sat Oct 20, 2012 1:32 pm (PDT) . Posted by:
"John Green" john_green1947
Hi, Carter,
What's your opinion (and anyone elses):
Taking the thinking of just needing a small cooler for coffee cream,
soda, cheese etc., and no freezing, could an automotive air conditioning
system be run at slow rpm using a windmill that might need to be geared
down?
It could always be set up with a 12v backup motor to turn the compressor
with the windmill de-clutched somehow.
John
3b. Re: 12V Accessories (Refrigeration)
Posted by: "Carter Quillen" [1]twowheelinguy@ yahoo.com twowheelinguy
Date: Fri Oct 19, 2012 9:19 am ((PDT))
Hey, more power to you if it works and I'm sure it does.
I'm just saying, you'll get far more refrigeration effect per Watt with
vapor co
mpression than any other approach. I have an off the shelf, 11 cu. ft.
refrigera
tor freezer on the Arc that I bought for $300 and I love it. It will
most likely
run for the next 10 years without missing a beat and I'll throw it away
and buy
a new one. There is no way I could produce that luxury with either
absorbtion o
r Petier technology for anywhere near that cost or efficiecncy.
That's all I'm saying.
--
http://www.fastmail .fm - Accessible with your email software
or over the web
Sat Oct 20, 2012 1:50 pm (PDT) . Posted by:
"Kirk McLoren" kirkmcloren
you lost it with small. An automobile compressor is sized, depending on application, at 1 to 2 tons. Lots of glass in a car and metal conducts well also. Rapid draw down is important. A sealed compressor with 1/8 that capacity will keep your cream cool. Assuming 50% efficiency mechanical work to electricity and then electricity to mechanical work you are at 1/4 horse versus 1 or 2. Besides in most warm places there is reliable sun. photovoltaics to battery to dedicated inverter is smaller and more reliable.
My 2 cents.
Will Rogers quote: "Stupidity got us into this – why can't it get us out?"
____________ _________ _________ __
From: John Green <v_2jgree@operamail. com>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:32 PM
Subject: [Electric Boats] Re: 12V Accessories (Refrigeration)
Hi, Carter,
What's your opinion (and anyone elses):
Taking the thinking of just needing a small cooler for coffee cream,
soda, cheese etc., and no freezing, could an automotive air conditioning
system be run at slow rpm using a windmill that might need to be geared
down?
It could always be set up with a 12v backup motor to turn the compressor
with the windmill de-clutched somehow.
John
3b. Re: 12V Accessories (Refrigeration)
Posted by: "Carter Quillen" [1]twowheelinguy@ yahoo.com twowheelinguy
Date: Fri Oct 19, 2012 9:19 am ((PDT))
Hey, more power to you if it works and I'm sure it does.
I'm just saying, you'll get far more refrigeration effect per Watt with
vapor co
mpression than any other approach. I have an off the shelf, 11 cu. ft.
refrigera
tor freezer on the Arc that I bought for $300 and I love it. It will
most likely
run for the next 10 years without missing a beat and I'll throw it away
and buy
a new one. There is no way I could produce that luxury with either
absorbtion o
r Petier technology for anywhere near that cost or efficiecncy.
That's all I'm saying.
--
http://www.fastmail .fm - Accessible with your email software
or over the web
My 2 cents.
Will Rogers quote: "Stupidity got us into this – why can't it get us out?"
____________ _________ _________ __
From: John Green <v_2jgree@operamail. com>
To: electricboats@ yahoogroups. com
Sent: Saturday, October 20, 2012 1:32 PM
Subject: [Electric Boats] Re: 12V Accessories (Refrigeration)
Hi, Carter,
What's your opinion (and anyone elses):
Taking the thinking of just needing a small cooler for coffee cream,
soda, cheese etc., and no freezing, could an automotive air conditioning
system be run at slow rpm using a windmill that might need to be geared
down?
It could always be set up with a 12v backup motor to turn the compressor
with the windmill de-clutched somehow.
John
3b. Re: 12V Accessories (Refrigeration)
Posted by: "Carter Quillen" [1]twowheelinguy@ yahoo.com twowheelinguy
Date: Fri Oct 19, 2012 9:19 am ((PDT))
Hey, more power to you if it works and I'm sure it does.
I'm just saying, you'll get far more refrigeration effect per Watt with
vapor co
mpression than any other approach. I have an off the shelf, 11 cu. ft.
refrigera
tor freezer on the Arc that I bought for $300 and I love it. It will
most likely
run for the next 10 years without missing a beat and I'll throw it away
and buy
a new one. There is no way I could produce that luxury with either
absorbtion o
r Petier technology for anywhere near that cost or efficiecncy.
That's all I'm saying.
--
http://www.fastmail .fm - Accessible with your email software
or over the web
Sat Oct 20, 2012 2:45 pm (PDT) . Posted by:
"Craig Carmichael" craigcarmichaelis
>Hello Craig, I purchased a name brand 44qt? cooler with peltier
>device for $85.00 online and picked up at local sears. Keep an eye
>on their site and you can once in a while catch this price.
Yes, I'm sure the camping cooler module is the simple starting point.
The things to add to that are the ice tray/chest on the inside
(replacing the inside heatsink and fan) and the (as yet unbuilt)
smart control.
The 3" extruded polystyrene foam (house insulation, R5 per inch) is a
key to success with a minimal cooling unit, and shapes with minimum
surface area for the volume like an octagon (or ideally a geodesic
dome) are valuable.
With 3" of insulation, 3 one gallon ice cream pails of ice kept the
floor temperature at 5-6ºC for 2-1/2 days, and it looked like they'd
take 3 or 4 days to melt completely. So a simple large superinsulated
icebox should be good enough for weekend excursions. Call it a better
insulated cooler.
Polyurethane foam, R7 per inch, is even better, but I found it more
mess and hassle than it was worth to make walls of, at least for
flat, square shapes. However, cans of PU spray foam make an
excellent, crack filling glue for gluing the sheets of PS together.
---
To start from scratch, look up 'Peltier modules' or 'peltier cooling'
to find the thin, flat peltier wafers. The surfaces are white ceramic
and the thermocouples are within. (Mine is rated 8.4 amps at 15+
volts, and draws about 7.2 amps at 13 volts, BTW.) Aluminum extruded
finned heatsinks seem overpriced to unavailable. I make heatsinks by
(a) taking 2 fat bars of aluminum and clamping several pieces of thin
aluminum between (with bolts right across between the two bars), then
bending the thin pieces (eg, roofing flashing) into a fan shape,
\ top bar /
\ \ ======= / /
\--\-------/ --/ <- fanned out
------------ -- <- flashing
__/--------- \__
========= <- bottom bar
[peltier]
=========
or (b) my new idea for the Peltier cooling with a fan blowing across
parallel fins: several 1/4" x 1/2" bars ("n") "stacked" together with
2" wide thin pieces ("|") for fins between them, bolted right across
from one side to the other: n|n|n|n|n|n| n|n... Or you might stack 2
fins per bar and bend them apart a bit.
Digikey is a bit pricey for peltiers (18$) compared to some people on
Amazon and other places (10$), but they have 12V fans from about 3$
up for the outside heat sink fan.
> I removed the exterior AL heat sink and replaced with a water
>cooled heat sink wi better fan ($38 online; used). Hope to find
>time next month to test for efficiency improvement (faster cooling),
>Also considered 'stacking peltier's but no time for that yet.
That should help a bit - keeping the outside cooler as with
circulating water gives you a few more watts of cooling energy for
the input watts, but making the ouside 10º cooler doesn't mean the
inside will be 10º cooler. (I mention this because I didn't realize
it at first. Heat is still leaking through the fridge walls at the
same rate and needs more watts for each degree cooler.) But there's a
Koolatron[.com iirc] cooler sized fridge unit (150-200$) with some
sort of passive refrigerant tubes heated by the Peltier outside unit
and they say it'll cool by up to 30ºC where most claim 20ºc.
Putting two Peltiers in series seems no more effective than a single
one - I tried it and then realized results were better with just one.
(If you want to have say 3 on the outside stage and 1 on the inside
colder stage it can get substantially colder, but for 4 times as much
electricity. )
Craig
===
Sat Oct 20, 2012 4:10 pm (PDT) . Posted by:
"Craig Carmichael" craigcarmichaelis
>I'm thinking that since one of the peltier's big issues is how to
>dissipate the waste heat, and since a boat is sitting in water, that
>maybe a peltier's hot plate could be formed into the external hull
>of a boat. This might be too scary for an ocean going sailboat, but
>for a small lake and river boat it might be a way to get the
>efficiency up while keeping the small size and the low maintenance.
Interesting thought! Maybe as a thick removable aluminum plate,
bolted on, with a gasket, in a square hole slightly recessed and with
reinforced edges inside for the job? Easily replaced if it eventually
looks too corroded. Of course with composite that'd best be built in
in advance. With an aluminum hull it'd be really simple.
>
>Either way, I applaud your big fridge.
>
>John
Thanks!
>dissipate the waste heat, and since a boat is sitting in water, that
>maybe a peltier's hot plate could be formed into the external hull
>of a boat. This might be too scary for an ocean going sailboat, but
>for a small lake and river boat it might be a way to get the
>efficiency up while keeping the small size and the low maintenance.
Interesting thought! Maybe as a thick removable aluminum plate,
bolted on, with a gasket, in a square hole slightly recessed and with
reinforced edges inside for the job? Easily replaced if it eventually
looks too corroded. Of course with composite that'd best be built in
in advance. With an aluminum hull it'd be really simple.
>
>Either way, I applaud your big fridge.
>
>John
Thanks!
Sat Oct 20, 2012 6:23 pm (PDT) . Posted by:
"william munger" gray_penguin
I studied making my own Refrigeration with Peltier devices, but that's
as far as I got.
Have you guys heard of this:
http://www.thermabl ok.com/
It is rather expensive but the R value is incredible.
William
> >I'm thinking that since one of the peltier's big issues is how to
> >dissipate the waste heat, and since a boat is sitting in water, that
> >maybe a peltier's hot plate could be formed into the external hull
> >of a boat. This might be too scary for an ocean going sailboat, but
> >for a small lake and river boat it might be a way to get the
> >efficiency up while keeping the small size and the low maintenance.
>
> Interesting thought! Maybe as a thick removable aluminum plate,
> bolted on, with a gasket, in a square hole slightly recessed and with
> reinforced edges inside for the job? Easily replaced if it eventually
> looks too corroded. Of course with composite that'd best be built in
> in advance. With an aluminum hull it'd be really simple.
>
> >
> >Either way, I applaud your big fridge.
> >
> >John
>
> Thanks!
>
>
as far as I got.
Have you guys heard of this:
http://www.thermabl ok.com/
It is rather expensive but the R value is incredible.
William
> >I'm thinking that since one of the peltier's big issues is how to
> >dissipate the waste heat, and since a boat is sitting in water, that
> >maybe a peltier's hot plate could be formed into the external hull
> >of a boat. This might be too scary for an ocean going sailboat, but
> >for a small lake and river boat it might be a way to get the
> >efficiency up while keeping the small size and the low maintenance.
>
> Interesting thought! Maybe as a thick removable aluminum plate,
> bolted on, with a gasket, in a square hole slightly recessed and with
> reinforced edges inside for the job? Easily replaced if it eventually
> looks too corroded. Of course with composite that'd best be built in
> in advance. With an aluminum hull it'd be really simple.
>
> >
> >Either way, I applaud your big fridge.
> >
> >John
>
> Thanks!
>
>
Sat Oct 20, 2012 7:33 pm (PDT) . Posted by:
"R.N. Little" solarboat1
You may want to review this sites home page. This link is to their 'water block' exchanger. In 04 I had to put a temp cut off as the 'camping cooler' was freezing soda at night. http://www.customth ermoelectric. com/Water_ blocks.html I use the water cooled heat exchanger to bring the temp down faster for day time frequent opening of the cabinet. Placing the 'radiator' component near the hull takes advantage of the cooler air there. Stacking is worth looking at and the links home page discusses this. Good luck with your project. Nick
--- On Sat, 10/20/12, Craig Carmichael <craig@saers. com> wrote:
From: Craig Carmichael <craig@saers. com>
Subject: Re: [Electric Boats] Re: 12V Accessories (Refrigeration)
To: electricboats@ yahoogroups. com
Date: Saturday, October 20, 2012, 2:48 PM
>Hello Craig, I purchased a name brand 44qt? cooler with peltier
>device for $85.00 online and picked up at local sears. Keep an eye
>on their site and you can once in a while catch this price.
Yes, I'm sure the camping cooler module is the simple starting point.
The things to add to that are the ice tray/chest on the inside
(replacing the inside heatsink and fan) and the (as yet unbuilt)
smart control.
The 3" extruded polystyrene foam (house insulation, R5 per inch) is a
key to success with a minimal cooling unit, and shapes with minimum
surface area for the volume like an octagon (or ideally a geodesic
dome) are valuable.
With 3" of insulation, 3 one gallon ice cream pails of ice kept the
floor temperature at 5-6ºC for 2-1/2 days, and it looked like they'd
take 3 or 4 days to melt completely. So a simple large superinsulated
icebox should be good enough for weekend excursions. Call it a better
insulated cooler.
Polyurethane foam, R7 per inch, is even better, but I found it more
mess and hassle than it was worth to make walls of, at least for
flat, square shapes. However, cans of PU spray foam make an
excellent, crack filling glue for gluing the sheets of PS together.
---
To start from scratch, look up 'Peltier modules' or 'peltier cooling'
to find the thin, flat peltier wafers. The surfaces are white ceramic
and the thermocouples are within. (Mine is rated 8.4 amps at 15+
volts, and draws about 7.2 amps at 13 volts, BTW.) Aluminum extruded
finned heatsinks seem overpriced to unavailable. I make heatsinks by
(a) taking 2 fat bars of aluminum and clamping several pieces of thin
aluminum between (with bolts right across between the two bars), then
bending the thin pieces (eg, roofing flashing) into a fan shape,
\ top bar /
\ \ ======= / /
\--\-------/ --/ <- fanned out
------------ -- <- flashing
__/--------- \__
========= <- bottom bar
[peltier]
=========
or (b) my new idea for the Peltier cooling with a fan blowing across
parallel fins: several 1/4" x 1/2" bars ("n") "stacked" together with
2" wide thin pieces ("|") for fins between them, bolted right across
from one side to the other: n|n|n|n|n|n| n|n... Or you might stack 2
fins per bar and bend them apart a bit.
Digikey is a bit pricey for peltiers (18$) compared to some people on
Amazon and other places (10$), but they have 12V fans from about 3$
up for the outside heat sink fan.
> I removed the exterior AL heat sink and replaced with a water
>cooled heat sink wi better fan ($38 online; used). Hope to find
>time next month to test for efficiency improvement (faster cooling),
>Also considered 'stacking peltier's but no time for that yet.
That should help a bit - keeping the outside cooler as with
circulating water gives you a few more watts of cooling energy for
the input watts, but making the ouside 10º cooler doesn't mean the
inside will be 10º cooler. (I mention this because I didn't realize
it at first. Heat is still leaking through the fridge walls at the
same rate and needs more watts for each degree cooler.) But there's a
Koolatron[.com iirc] cooler sized fridge unit (150-200$) with some
sort of passive refrigerant tubes heated by the Peltier outside unit
and they say it'll cool by up to 30ºC where most claim 20ºc.
Putting two Peltiers in series seems no more effective than a single
one - I tried it and then realized results were better with just one.
(If you want to have say 3 on the outside stage and 1 on the inside
colder stage it can get substantially colder, but for 4 times as much
electricity. )
Craig
===
--- On Sat, 10/20/12, Craig Carmichael <craig@saers. com> wrote:
From: Craig Carmichael <craig@saers. com>
Subject: Re: [Electric Boats] Re: 12V Accessories (Refrigeration)
To: electricboats@ yahoogroups. com
Date: Saturday, October 20, 2012, 2:48 PM
>Hello Craig, I purchased a name brand 44qt? cooler with peltier
>device for $85.00 online and picked up at local sears. Keep an eye
>on their site and you can once in a while catch this price.
Yes, I'm sure the camping cooler module is the simple starting point.
The things to add to that are the ice tray/chest on the inside
(replacing the inside heatsink and fan) and the (as yet unbuilt)
smart control.
The 3" extruded polystyrene foam (house insulation, R5 per inch) is a
key to success with a minimal cooling unit, and shapes with minimum
surface area for the volume like an octagon (or ideally a geodesic
dome) are valuable.
With 3" of insulation, 3 one gallon ice cream pails of ice kept the
floor temperature at 5-6ºC for 2-1/2 days, and it looked like they'd
take 3 or 4 days to melt completely. So a simple large superinsulated
icebox should be good enough for weekend excursions. Call it a better
insulated cooler.
Polyurethane foam, R7 per inch, is even better, but I found it more
mess and hassle than it was worth to make walls of, at least for
flat, square shapes. However, cans of PU spray foam make an
excellent, crack filling glue for gluing the sheets of PS together.
---
To start from scratch, look up 'Peltier modules' or 'peltier cooling'
to find the thin, flat peltier wafers. The surfaces are white ceramic
and the thermocouples are within. (Mine is rated 8.4 amps at 15+
volts, and draws about 7.2 amps at 13 volts, BTW.) Aluminum extruded
finned heatsinks seem overpriced to unavailable. I make heatsinks by
(a) taking 2 fat bars of aluminum and clamping several pieces of thin
aluminum between (with bolts right across between the two bars), then
bending the thin pieces (eg, roofing flashing) into a fan shape,
\ top bar /
\ \ ======= / /
\--\-------/ --/ <- fanned out
------------ -- <- flashing
__/--------- \__
========= <- bottom bar
[peltier]
=========
or (b) my new idea for the Peltier cooling with a fan blowing across
parallel fins: several 1/4" x 1/2" bars ("n") "stacked" together with
2" wide thin pieces ("|") for fins between them, bolted right across
from one side to the other: n|n|n|n|n|n| n|n... Or you might stack 2
fins per bar and bend them apart a bit.
Digikey is a bit pricey for peltiers (18$) compared to some people on
Amazon and other places (10$), but they have 12V fans from about 3$
up for the outside heat sink fan.
> I removed the exterior AL heat sink and replaced with a water
>cooled heat sink wi better fan ($38 online; used). Hope to find
>time next month to test for efficiency improvement (faster cooling),
>Also considered 'stacking peltier's but no time for that yet.
That should help a bit - keeping the outside cooler as with
circulating water gives you a few more watts of cooling energy for
the input watts, but making the ouside 10º cooler doesn't mean the
inside will be 10º cooler. (I mention this because I didn't realize
it at first. Heat is still leaking through the fridge walls at the
same rate and needs more watts for each degree cooler.) But there's a
Koolatron[.com iirc] cooler sized fridge unit (150-200$) with some
sort of passive refrigerant tubes heated by the Peltier outside unit
and they say it'll cool by up to 30ºC where most claim 20ºc.
Putting two Peltiers in series seems no more effective than a single
one - I tried it and then realized results were better with just one.
(If you want to have say 3 on the outside stage and 1 on the inside
colder stage it can get substantially colder, but for 4 times as much
electricity. )
Craig
===
Sat Oct 20, 2012 8:18 pm (PDT) . Posted by:
"jcglt - FK8IH" jcglt
I'm the owner of a Torqeedo 503S which I mainly use for the propulsion of my tender.
I've however one question : what would happen if this engine was free wheeling behind my sailboat at a speed of around 6 to 8 knots ? Would it generate 12V DC or nothing because it has not been designed as a generator ?
jcglt - S/Y Bauhinia
I've however one question : what would happen if this engine was free wheeling behind my sailboat at a speed of around 6 to 8 knots ? Would it generate 12V DC or nothing because it has not been designed as a generator ?
jcglt - S/Y Bauhinia
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