Thanks all for your assistance.
Doug
On Saturday, February 22, 2014 5:11 AM, "electricboats@yahoogroups.com" <electricboats@yahoogroups.com> wrote:
4 Messages
Digest #3669
Messages
Fri Feb 21, 2014 6:43 am (PST) . Posted by:
mkriley48
I guess if you have a lot of battery banks and a big enough engine you will not be useing any power at all??
mike
mike
Fri Feb 21, 2014 8:28 am (PST) . Posted by:
"oak" oak_box
Um, so I guess this was taken out of context a bit.
The reference comparison was between a 48V Torqeedo 4R vs. a 24V Torqeedo 2R.
It turns out that both motors have the same prop (at least from the spec I looked at).
The 48V 4R is spec'd to run at a max of 4kW. Mine tops out around 3500W.
The 24V 2R is spec'd to run at a max of 2kW.
I have one of each, and get about the same boat speed on my C-22 if I run either motor at 1000W (about 4.3mph).
If you have the SAME 4 batteries, you can configure them either as 48V in series, or as 24V as two 24V banks in parallel.
Run BOTH motors at 1000W.
The 48V systems will draw about 20.8A from all 4 batteries in series.
The 24V system will draw about 41.6A - which is a fairly heavy load. But if you split that between two banks in parallel, you get back to the 20A per bank.
The FIRST POINT was that you can get a 24V system going with just 2 batteries - though the amps consumed for an equivalent power (to the 48V system) would be greater than the amp draw from a 48V system.
Peukert effect holds, and I have seen that if I try to draw 40A from a 24V bank, that the batteries run down faster than pulling 20A from the same bank for twice as long. But it will work for shorter periods of time to get started.
The SECOND POINT was that the Torqeedo 4R can run at a substantially higher power level than the 2R. For my C-22, that's not needed. For Doug's boat, it might be nice to have the option to run at closer to 3kW.
____________ _________ _________ __
From: "mkriley48@yahoo. com" <mkriley48@yahoo. com>
To: electricboats@ yahoogroups. com
Sent: Friday, February 21, 2014 8:43 AM
Subject: Re: [Electric Boats] Torqueedo 2.0, a good fit?
I guess if you have a lot of battery banks and a big enough engine you will not be useing any power at all??
mike
The reference comparison was between a 48V Torqeedo 4R vs. a 24V Torqeedo 2R.
It turns out that both motors have the same prop (at least from the spec I looked at).
The 48V 4R is spec'd to run at a max of 4kW. Mine tops out around 3500W.
The 24V 2R is spec'd to run at a max of 2kW.
I have one of each, and get about the same boat speed on my C-22 if I run either motor at 1000W (about 4.3mph).
If you have the SAME 4 batteries, you can configure them either as 48V in series, or as 24V as two 24V banks in parallel.
Run BOTH motors at 1000W.
The 48V systems will draw about 20.8A from all 4 batteries in series.
The 24V system will draw about 41.6A - which is a fairly heavy load. But if you split that between two banks in parallel, you get back to the 20A per bank.
The FIRST POINT was that you can get a 24V system going with just 2 batteries - though the amps consumed for an equivalent power (to the 48V system) would be greater than the amp draw from a 48V system.
Peukert effect holds, and I have seen that if I try to draw 40A from a 24V bank, that the batteries run down faster than pulling 20A from the same bank for twice as long. But it will work for shorter periods of time to get started.
The SECOND POINT was that the Torqeedo 4R can run at a substantially higher power level than the 2R. For my C-22, that's not needed. For Doug's boat, it might be nice to have the option to run at closer to 3kW.
____________ _________ _________ __
From: "mkriley48@yahoo. com" <mkriley48@yahoo. com>
To: electricboats@ yahoogroups. com
Sent: Friday, February 21, 2014 8:43 AM
Subject: Re: [Electric Boats] Torqueedo 2.0, a good fit?
I guess if you have a lot of battery banks and a big enough engine you will not be useing any power at all??
mike
Fri Feb 21, 2014 8:42 am (PST) . Posted by:
mikegunning@ymail.com
Your boat at 5000 pounds seems a little heavy for a 22ft cat boat. To push her, think in terms of watts (power). The Torqeedo 2.0 is a 2000w motor. Our numbers for you boat with a well placed and balanced propeller indicates 2kW is a little light, the 4.0 would be a better fit. A 5kW (it will be a 48v system) inboard would be the best fit.
Speed & Power in calm waters:
Kts Watts
3.0 480
3.8 960
4.8 1920
5.5 2880
6.5 4800
Hull speed 6.29
The 2kW in best conditions will give you 75%of hull speed and in poor conditions significantly less.
Regarding battery they are not all alike and to compare one group 31 to another group 31 should be like for like. With batteries a key number to look at the number of cycles for the depth of discharge (DOD). We believe a minimum cycle of 300 DOD of 80% to be appropriate traction batteries for use as marine propulsion. Lifeline AGM batteries are the standard for you to compare lead acid batteries. Your needs and skill should dictate what is the best motor and battery for you, not what cost less.
Mike
Electric Yachts of Southern California
Speed & Power in calm waters:
Kts Watts
3.0 480
3.8 960
4.8 1920
5.5 2880
6.5 4800
Hull speed 6.29
The 2kW in best conditions will give you 75%of hull speed and in poor conditions significantly less.
Regarding battery they are not all alike and to compare one group 31 to another group 31 should be like for like. With batteries a key number to look at the number of cycles for the depth of discharge (DOD). We believe a minimum cycle of 300 DOD of 80% to be appropriate traction batteries for use as marine propulsion. Lifeline AGM batteries are the standard for you to compare lead acid batteries. Your needs and skill should dictate what is the best motor and battery for you, not what cost less.
Mike
Electric Yachts of Southern California
Fri Feb 21, 2014 6:53 pm (PST) . Posted by:
cirejay
The displacement of the 22' Marshall cat (fiberglass) is 5500 so 5000 for a wooden cat doesn't seem particularly off base.
eric SV Meander
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Your boat at 5000 pounds seems a little heavy for a 22ft cat boat. To push her, think in terms of watts (power). The Torqeedo 2.0 is a 2000w motor. Our numbers for you boat with a well placed and balanced propeller indicates 2kW is a little light, the 4.0 would be a better fit. A 5kW (it will be a 48v system) inboard would be the best fit.
Speed & Power in calm waters:
Kts Watts
3.0 480
3.8 960
4.8 1920
5.5 2880
6.5 4800
Hull speed 6.29
The 2kW in best conditions will give you 75%of hull speed and in poor conditions significantly less.
Regarding battery they are not all alike and to compare one group 31 to another group 31 should be like for like. With batteries a key number to look at the number of cycles for the depth of discharge (DOD). We believe a minimum cycle of 300 DOD of 80% to be appropriate traction batteries for use as marine propulsion. Lifeline AGM batteries are the standard for you to compare lead acid batteries. Your needs and skill should dictate what is the best motor and battery for you, not what cost less.
Mike
Electric Yachts of Southern California
eric SV Meander
............ ......... ......... ......... ......... ......... ......... ......... ......... ......... ......... ......... .......
Your boat at 5000 pounds seems a little heavy for a 22ft cat boat. To push her, think in terms of watts (power). The Torqeedo 2.0 is a 2000w motor. Our numbers for you boat with a well placed and balanced propeller indicates 2kW is a little light, the 4.0 would be a better fit. A 5kW (it will be a 48v system) inboard would be the best fit.
Speed & Power in calm waters:
Kts Watts
3.0 480
3.8 960
4.8 1920
5.5 2880
6.5 4800
Hull speed 6.29
The 2kW in best conditions will give you 75%of hull speed and in poor conditions significantly less.
Regarding battery they are not all alike and to compare one group 31 to another group 31 should be like for like. With batteries a key number to look at the number of cycles for the depth of discharge (DOD). We believe a minimum cycle of 300 DOD of 80% to be appropriate traction batteries for use as marine propulsion. Lifeline AGM batteries are the standard for you to compare lead acid batteries. Your needs and skill should dictate what is the best motor and battery for you, not what cost less.
Mike
Electric Yachts of Southern California
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