Saturday, April 30, 2016

[Electric Boats] Re: Batteries wired in parallel (and series...)

 

How about monitoring the temperature of each battery?  Temperature sensors/switches are cheap and easy to interface:
 
http://www.digikey.com/product-detail/en/microchip-technology/TC622VAT/TC622VAT-ND/418685

Thermal characteristics of lead acid is well documented, although historically in terms of battery charging where proper charging needs temperature compensation.  Also, much of the information on thermal issues has been in moderate current deep cycle (see the previous cited AmplePower reference).  But in electric power vehicles high continuous currents are more of an issue.

Miles' discussion about the problems of fusing was good, and circuit protection must be built into any system.  That can get complex, especially in terms of protecting an individual battery.  But we seem to be overlooking what can be done by monitoring the temperature of each battery and using that for alarms or system shut down on thermal runaway.

John Acord
Flatwater Electronics
www.flatwaterfarm.com
"Neurosurgery for computer looms."

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Friday, April 29, 2016

Re: [Electric Boats] Re: Batteries wired in parallel (and series...)

 

I somewhat disagree with your somewhat disagreement.

The  8 220ah 6v batteries I am using cost me $85/ea. If I wanted batteries of twice that capacity I would have spent a lot more money per kw/hr. Also when I installed the original bank I could not have afforded anything bigger, or more of what I did get. In order to avoid parallel batteries, and in order to even be able to afford a bank in the first place, and to have enough capacity to motor around out in Lake Pontchartrain all day, I had to go with the golf cart batteries. For me, cost dictates practically EVERYTHING, and so I am very conscious not only of spending my money where and how it will do the most good, but also staying within a very very tight budget.

Now, I could use more capacity, and I have a few dollars to buy more batteries, but certainly not enough money to try to find 440ah  or bigger batteries. And then... what to do with the original bank... discard it, after only two years of reasonably good care and fairly light use? I don't think so. So the obvious thing to do is to buy exactly the same thing I bought the first time. And rather than charging and discharging them in parallel, with their 2 year age difference, I will run them as separate straight series banks. Even if both sets of batteries were the exact same age, I would still prefer series rather than parallel. (Of course, putting them all together in series for 96v would be an interesting option, too, but I would need a different controller and a different motor than what I have.)

So, what I have done and what I am doing and what I plan to do, is the most cost effective route for me. You might not be as financially constrained, and might be able to afford bigger or better batteries, and do things the "ideal" way. It was not possible for me and it is not possible for me now. But rather than sit and sulk and dream about one day being able to put an electric boat together the "right" way, I chose to just do it the best way that I could, and I did it. It works, and it is working better with each incremental improvement I am able to make.

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Re: [Electric Boats] Re: Batteries wired in series

 

When you are using a multi-meter to check battery voltage, be careful also.
If you happen to be chasing a posible voltage drain on your system and plug your leads into the 10A current connections.
Go for dinner and come back and grab the multimeter and change it to check voltage, but leave it connected to the 10A connection. On a 72 volt fully charged system, the multimeter lead will vapourize in less than a second.
Also always use eye protection just incase.
Maybe not all meters do this but mine did, suspect it is because there is a shunt internally on this setting.

Mark

--------------------------------------------
On Thu, 4/28/16, 'Jason (Electric Boats) Taylor' jt.yahoo@jtaylor.ca [electricboats] <electricboats@yahoogroups.com> wrote:

Subject: Re: [Electric Boats] Re: Batteries wired in series
To: electricboats@yahoogroups.com
Received: Thursday, April 28, 2016, 4:35 AM


 









The main precautions to take are to make
sure you don't simultaneously contact more than one
exposed terminal on your batteries. I modified a ratchet
driver and dedicated it to the engine room. I simply sleeved
the metal handle with heat shrink tube, and this is the ONLY
tool I use when the battery cover is off. I have had a
tool-drop short circuit before. I don't want one
again. 
--Jason
Taylorv:514-815-8204e:j@jtaylor.ca
On Apr 28,
2016, at 3:26 AM, Hannu Venermo gcode.fi@gmail.com
[electricboats] <electricboats@yahoogroups.com>
wrote:
















 









Its DC.
A shock involves touching two wires, the + and the
-.
Grounding is not involved (or present).

All dc wires are connected point to point.
DC is considered "safe" at 48V DC, upto
approx 80V.
Low voltage does not want to go through humans. We
have high
10Mohm resistance, more or less, and poor
conductivity.




On 28/04/2016
04:22, king_of_neworleans
wrote:


As
long as you are not grounded you can touch any
connection in the
system and not get a shock. But better to simply not
touch any
bare conductor in the first place.


--
-hanermo (cnc designs)


























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Re: [Electric Boats] Re: Batteries wired in parallel (and series...)

 

I somewhat disagree.
You are getting 1/3 of your moneys worth, with this arrangement.

Shallow-cycling one big battery has 3-10x the lifetime, and the bigger it is the closer to 10x.


On 29/04/2016 16:14, king_of_neworleans wrote:
The dangers inherent with series/parallel flooded cell banks are perhaps overstated, yeah. Nevertheless I would point out that it is also quite do-able to simply make two separate series banks. Yes there are disadvantages to this if the batteries are of low capacity relative to peak discharge rate, but there is also the psychological advantage of knowing if one bank got you somewhere, then the other one should get you home. I myself would normally prefer a second bank over paralleling the batteries.

--   -hanermo (cnc designs)

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Re: [Electric Boats] Batteries wired in parallel (and series...)

 

My whole-house UPS system recently suffered a battery failure.
The setup is 4 parallel banks of 20 12V*7ah SLAs wired in series, in two
groups of 10.
The reason for this setup is the modular nature of the UPS. You buy one
UPS master controller, a separate Isolation transformer module and at
least one battery pack. Additional packs are daisy-chained together in
a parallel arrangement. Each battery module has a 3-pole breaker at
0V-120V-240V points.
For those interested, it is the MGE EX 5 RT:
http://www.mgemexico.com/pdf/EX_RT_manual.pdf
The whole setup weighs about 800lbs and provides a 240V 30A sub-panel
which is enough to keep my lights, fridge, sump pump and technology
powered -- everything except big appliances -- in the event of a power
failure. It allows me to sleep through the night, calmly wake up,
realize there is a problem and start the generator in the morning. I
acquired it at a bankruptcy auction for all of $200. I am very happy
with it :-)

Anyway, I had two 12v batteries fail in one of the modules -- it was a
thermal event with melted plastic, acidic smoke and everything,
including questions from the wife as to what the bloody hell was going
on and was the house going to burn down and why do we need this thing
anyway??!.
The 20 batteries in series of this module happily drained into this
short. By the time I noticed the sulfery smell, each battery in this
module was already reading below 8V, many were simply at zero and were
essentially inert lumps of lead and plastic.
the breaker on this module had tripped, under high load. It was toast.
But it went out doing its job. The other three modules were working
just fine. Without those battery module breakers, I have no doubt that
there would have been a house-evacuation event, perhaps a late-night
sound and light show for the neighbours provided by the local fire
department.

Long story short, two faulty batteries took down all the batteries in
that series set.
The breaker protected the other series sets connected in parallel.
If I hadn't had the parallel breakers, I would have lost 80 SLA
batteries -- about $1200 to replace instead of the more modest $300 of
this one failure.

The moral of the story is to always have some kind of fuse between
parallel sets. Always.
James is right. Everything will be fine for identical batteries in
parallel. But it's toward the end of the life of these batteries that
"same" will no longer apply to the two batteries. And it's a this point
that one will decide to drain into the other. In a big way. 2/0
battery cable can carry an awful lot of current. Especially over the
short distances between a pair of cells. The cable will not be the
current limiter in the connection. The electrolyte or the terminals
will. So either the terminals will melt and break the connection that
way or the electrolyte will flash into steam and have a sudden and
intense desire to take up more space. Lots more space. Paralleled
batteries are just fine... until they're not.

/Jason

On 2016-04-29 11:35, oak oak_box@yahoo.com [electricboats] wrote:
> Side note - if one properly installs fuses on each string that is
> added in parallel, hopefully that would at least help protect against
> the case of a single dead battery causing the parallel string to do a
> massive discharge.
>
> John
>
> -------------------------
> FROM: "aweekdaysailor@yahoo.com [electricboats]"
> <electricboats@yahoogroups.com>
> TO: electricboats@yahoogroups.com
> SENT: Thursday, April 28, 2016 4:45 PM
> SUBJECT: [Electric Boats] Batteries wired in parallel (and series...)
>
> [I didn't want to hijack the other thread on series...]
>
> Hi Folks, I am formerly active member and have been away a long time,
> but I still have the boat (Aja, 30' 1978 Hunter) and she is still
> electric (but I caved and installed an outboard...I am on SF bay after
> all...)
>
> So...I noticed someone who sounded quite sensible/knowledgeable
> recently posted concerns about wiring batteries in parallel. The issue
> being (if I understood correctly) that a short in one cell will
> potentially cause high amp discharge from the remaining paired
> battery(ies) into the shorted unit potentially causing explosion,
> fire, acid, screaming...
>
> That had me a bit concerned since I have a "buddy" string setup. 8 x
> 12v deep-cycle (sorta..) batteries, a pair wired in parallel and then
> the paired "buddies" connected for 48V. This has served me quite well
> (going on 10 years now) and I'm getting very good battery life in
> general. I occasionally re-balance the batteries using a high-amp
> automotive tester and pair weak with good, etc. (if really weak I head
> to Walmart for another...)
>
> I do independently charge the "buddies" so I am not using a 48V
> charger.
>
> However, in counter to the concern, I did find this article Parallel
> Batteries [1] which seems to dismiss the concern.
>
> [1]
>
> Parallel Batteries [1]
> Parallel Batteries
>
> View on www.amplepower.com [1]
> Preview by Yahoo
>
> So...what say the gang? Dangerous? Or (within reason..) Safe? To save
> you a little reading, I've quoted the relevant section below:
>
> "Curiously, (or perhaps not so,) reference 1 does not list plate
> shorts as a failure mechanism of deep cycle batteries. Cell shorts are
> a significant failure in starting and lighting batteries, but not in
> deep cycle batteries which use better plate separators. Cell shorts
> are possible, however, and as reference 2 points out on pages 30-31,
> cell shorts can occur when a cell has been allowed to selfdischarge
> too deeply and the lead sulfate become soluable enough to diffuse
> through the separator. A den drite is then formed on recharge which
> conducts most of the current through the cell.
> Cells which short rarely do so with a low resistance. A cell is made
> up of alternating negative and positive plates having an intervening
> separator. Shorts between adjacent plates, are usually a dendrite or a
> local failure of the separator. It's fortunate that cell shorts are
> not normally low resistance. Consider a 200 Amp hour cell. Suppose
> that the cell developed a short that allowed 100 Amps to flow. At that
> current, a 2 Volt cell would be producing 200 Watts of power across
> the short. A 200 Ah cell could support 100 Amps of current for about
> 30 minutes. During that 30 minutes, in excess of 340 Btu of heat would
> be generated. There is 25-40 pounds of active material in a 200 Ah
> cell, which will rise to the boiling temperature of water in about 10
> minutes. The cell probably ceases to be a battery before boiling is
> reached. Assum ing that it doesn't, we would have enough Btu left,
> (210), to boil about 1/2 cup of electrolyte. That's a lot of steam!
> Obviously, if cells did short with a low resistance, batteries would
> be much more hazardous than they are. We'd have to mount batteries in
> special cases that could deal with the heat and acid steam. And given
> such dangers, there would be regulatory limits on the size of cells
> that could be manufactured. To get any reasonable capacity a large
> number of small cells would have to be paralleled. Hmmm.
> As mentioned, a cell rarely, if ever, shorts with a low resistance.
> Some people would have us believe that a shorted cell in one battery
> of a multi-battery bank will cause a fire. The argument goes that the
> remaining batteries will rapidly discharge through the cells of the
> defective battery. Such huge discharge, the story continues, will
> create an inferno with batteries boiling like a Boston tea kettle,
> spewing hell infinitely in all directions. Battery cases will blow
> gaping holes in their sides leaving a rather untidy mess for the maid.
> It makes us want to wear our rain gear every time we inspect our
> batteries to find out if any unauthorized cold fusion experiments are
> occurring."
>
> [also...within a couple of months I may have some interesting news
> relevant to the industry..teaser...]
>
> -Keith
>
>
>
> Links:
> ------
> [1] http://www.amplepower.com/pwrnews/parallel/
> [2]
> https://groups.yahoo.com/neo/groups/electricboats/conversations/messages/27374;_ylc=X3oDMTJxNTdjZmo0BF9TAzk3MzU5NzE0BGdycElkAzUyMTQzODIEZ3Jwc3BJZAMxNzA1ODg0MDkwBG1zZ0lkAzI3Mzc0BHNlYwNmdHIEc2xrA3JwbHkEc3RpbWUDMTQ2MTk0NDE1Mg--?act=reply&messageNum=27374
> [3]
> https://groups.yahoo.com/neo/groups/electricboats/conversations/newtopic;_ylc=X3oDMTJlYTc5MmczBF9TAzk3MzU5NzE0BGdycElkAzUyMTQzODIEZ3Jwc3BJZAMxNzA1ODg0MDkwBHNlYwNmdHIEc2xrA250cGMEc3RpbWUDMTQ2MTk0NDE1Mg--
> [4]
> https://groups.yahoo.com/neo/groups/electricboats/conversations/topics/27373;_ylc=X3oDMTM2NXFuZmI5BF9TAzk3MzU5NzE0BGdycElkAzUyMTQzODIEZ3Jwc3BJZAMxNzA1ODg0MDkwBG1zZ0lkAzI3Mzc0BHNlYwNmdHIEc2xrA3Z0cGMEc3RpbWUDMTQ2MTk0NDE1MgR0cGNJZAMyNzM3Mw--
> [5] https://yho.com/1wwmgg
> [6]
> https://groups.yahoo.com/neo/groups/electricboats/info;_ylc=X3oDMTJlMXQyOWhvBF9TAzk3MzU5NzE0BGdycElkAzUyMTQzODIEZ3Jwc3BJZAMxNzA1ODg0MDkwBHNlYwN2dGwEc2xrA3ZnaHAEc3RpbWUDMTQ2MTk0NDE1Mg--
> [7]
> https://groups.yahoo.com/neo/groups/electricboats/members/all;_ylc=X3oDMTJmcWt1ajNkBF9TAzk3MzU5NzE0BGdycElkAzUyMTQzODIEZ3Jwc3BJZAMxNzA1ODg0MDkwBHNlYwN2dGwEc2xrA3ZtYnJzBHN0aW1lAzE0NjE5NDQxNTI-
> [8]
> https://groups.yahoo.com/neo/groups/electricboats/photos/photostream;_ylc=X3oDMTJmNjRwYjU3BF9TAzk3MzU5NzE0BGdycElkAzUyMTQzODIEZ3Jwc3BJZAMxNzA1ODg0MDkwBHNlYwN2dGwEc2xrA3ZwaG90BHN0aW1lAzE0NjE5NDQxNTI-
> [9]
> https://groups.yahoo.com/neo;_ylc=X3oDMTJkYmZjbGNsBF9TAzk3NDc2NTkwBGdycElkAzUyMTQzODIEZ3Jwc3BJZAMxNzA1ODg0MDkwBHNlYwNmdHIEc2xrA2dmcARzdGltZQMxNDYxOTQ0MTUy
> [10] https://info.yahoo.com/privacy/us/yahoo/groups/details.html
> [11] https://info.yahoo.com/legal/us/yahoo/utos/terms/

--
Jason Taylor
--
S/V Fugu
1978 Beneteau First 30
Electroprop PM-20

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RE: [Electric Boats] Batteries wired in parallel (and series...)

 

John offered:

"Side note - if one properly installs fuses on each string that is added in parallel, hopefully that would at least help protect against the case of a single dead battery causing the parallel string to do a massive discharge."

 

That's a good point --- and a point well taken for folks paralleling Lithium also (as in my case).  Fuse size and wire lengths become important---you could figure that fusing at just over half the maximum current draw planned.  However, let's say that your buddies are not collocated but instead a distance away.  Path length and cable resistance may result in less current flowing thru the distant battery unless configuring the cabling such that there's a balanced path so that neither battery gets a short path.  In my case, I'm running with 7 Lithium batteries (31-48v @ 3kwh each) all connected up in parallel---ultimately I'll have 10-12 of these for a 30-36kwh pack.  Yet these batteries are located in 4 locations around the boat, with about 10ft separation Fore-Aft and about 4ft Port-Starboard between the subpacks.  And each of these battery modules actually has 2 sub-batteries.  You can easily imagine wildly different currents being drawn from each of these modules---so what size fuses do I use if maximum draw is under 250amps total?  Can they all be the same size?  Is it necessary to perfectly balance the cabling so each module path has the same resistance as any other?  How to avoid a "zipper" or cascade fuse blowing event?

 

That last question is one that's really important to consider.  So you choose to make all your fuse the same size, then you're cruising along and suddenly the boat motor stops.  You find that all the fuses have blown on one of your buddy pairs (or in my case, all 14-24 submodule fuses).  This would happen if the current rating on the fuses isn't sufficiently higher than needed or your battery configuration isn't sufficiently balanced such that one of the buddies sees current exceeding the fuse rating while the other(s) see less.  So the fuse blows---you're still motoring along and don't know anything happened, then a fraction of a second later, the buddy fuse(s) blow, "zippering" quickly out in sequence as a greater amount of current ends up flowing thru the remaining buddies' fuses.  This is an important design decision and one that I'm currently involved in not just for my boat but with a friend's boat's repowering.

I'll be using 20amp fuses primarily, which for the most part is total overkill.  But I'll also be carrying along some 60-80amp fuses to handle the case of for some reason having to run on a couple of batteries for a time.  Initially I've used industrial tubular fuses and holders, but I'm now switching over to the 8ga "Maxi" style 60-80amp fuse holders and fuses.  These are available pretty cheap these days from vendors on Ebay.

 

In case this helps-

 

-Myles Twete, Portland, Or.

www.evalbum.com/492

 

 

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Re: [Electric Boats] Batteries wired in parallel (and series...)

 

It takes less than 10 amps to create and sustain a thermal in a battery in parallel.   You cannot fuse for it because it is such a small current.   The only batteries that you can parallel safely are Pure Lead batteries.   Any other battery is potentially very dangerous when hooked in parallel at the end of the batteries life.   

James Lambden
Electroprop
6 Harbor Way #226
Santa Barbara, CA
93109


On Apr 29, 2016, at 8:35 AM, oak oak_box@yahoo.com [electricboats] <electricboats@yahoogroups.com> wrote:

 

Side note - if one properly installs fuses on each string that is added in parallel, hopefully that would at least help protect against the case of a single dead battery causing the parallel string to do a massive discharge.

John


From: "aweekdaysailor@yahoo.com [electricboats]" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Thursday, April 28, 2016 4:45 PM
Subject: [Electric Boats] Batteries wired in parallel (and series...)

 
[I didn't want to hijack the other thread on series...]

Hi Folks, I am formerly active member and have been away a long time, but I still have the boat (Aja, 30' 1978 Hunter) and she is still electric (but I caved and installed an outboard...I am on SF bay after all...)

So...I noticed someone who sounded quite sensible/knowledgeable recently posted concerns about wiring batteries in parallel. The issue being (if I understood correctly) that a short in one cell will potentially cause high amp discharge from the remaining paired battery(ies) into the shorted unit potentially causing explosion, fire, acid, screaming...

That had me a bit concerned since I have a "buddy" string setup. 8 x 12v deep-cycle (sorta..) batteries, a pair wired in parallel and then the paired "buddies" connected for 48V. This has served me quite well (going on 10 years now)  and I'm getting very good battery life in general. I occasionally re-balance the batteries using a high-amp automotive tester and pair weak with good, etc. (if really weak I head to Walmart for another...)

I do independently charge the "buddies" so I am not using a 48V charger. 

However, in counter to the concern, I did find this article Parallel Batteries which seems to dismiss the concern. 

So...what say the gang? Dangerous? Or (within reason..) Safe? To save you a little reading, I've quoted the relevant section below:

"Curiously, (or perhaps not so,) reference 1 does not list plate shorts as a failure mechanism of deep cycle batteries. Cell shorts are a significant failure in starting and lighting batteries, but not in deep cycle batteries which use better plate separators. Cell shorts are possible, however, and as reference 2 points out on pages 30-31, cell shorts can occur when a cell has been allowed to selfdischarge too deeply and the lead sulfate become soluable enough to diffuse through the separator. A dendrite is then formed on recharge which conducts most of the current through the cell.
Cells which short rarely do so with a low resistance. A cell is made up of alternating negative and positive plates having an intervening separator. Shorts between adjacent plates, are usually a dendrite or a local failure of the separator. It's fortunate that cell shorts are not normally low resistance. Consider a 200 Amp hour cell. Suppose that the cell developed a short that allowed 100 Amps to flow. At that current, a 2 Volt cell would be producing 200 Watts of power across the short. A 200 Ah cell could support 100 Amps of current for about 30 minutes. During that 30 minutes, in excess of 340 Btu of heat would be generated. There is 25-40 pounds of active material in a 200 Ah cell, which will rise to the boiling temperature of water in about 10 minutes. The cell probably ceases to be a battery before boiling is reached. Assuming that it doesn't, we would have enough Btu left, (210), to boil about 1/2 cup of electrolyte. That's a lot of steam!
Obviously, if cells did short with a low resistance, batteries would be much more hazardous than they are. We'd have to mount batteries in special cases that could deal with the heat and acid steam. And given such dangers, there would be regulatory limits on the size of cells that could be manufactured. To get any reasonable capacity a large number of small cells would have to be paralleled. Hmmm.
As mentioned, a cell rarely, if ever, shorts with a low resistance. Some people would have us believe that a shorted cell in one battery of a multi-battery bank will cause a fire. The argument goes that the remaining batteries will rapidly discharge through the cells of the defective battery. Such huge discharge, the story continues, will create an inferno with batteries boiling like a Boston tea kettle, spewing hell infinitely in all directions. Battery cases will blow gaping holes in their sides leaving a rather untidy mess for the maid. It makes us want to wear our rain gear every time we inspect our batteries to find out if any unauthorized cold fusion experiments are occurring." 


[also...within a couple of months I may have some interesting news relevant to the industry..teaser...]

-Keith
 


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Posted by: "james@electroprop.com" <james@electroprop.com>
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Re: [Electric Boats] Batteries wired in parallel (and series...)

 

Side note - if one properly installs fuses on each string that is added in parallel, hopefully that would at least help protect against the case of a single dead battery causing the parallel string to do a massive discharge.

John


From: "aweekdaysailor@yahoo.com [electricboats]" <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Thursday, April 28, 2016 4:45 PM
Subject: [Electric Boats] Batteries wired in parallel (and series...)

 
[I didn't want to hijack the other thread on series...]

Hi Folks, I am formerly active member and have been away a long time, but I still have the boat (Aja, 30' 1978 Hunter) and she is still electric (but I caved and installed an outboard...I am on SF bay after all...)

So...I noticed someone who sounded quite sensible/knowledgeable recently posted concerns about wiring batteries in parallel. The issue being (if I understood correctly) that a short in one cell will potentially cause high amp discharge from the remaining paired battery(ies) into the shorted unit potentially causing explosion, fire, acid, screaming...

That had me a bit concerned since I have a "buddy" string setup. 8 x 12v deep-cycle (sorta..) batteries, a pair wired in parallel and then the paired "buddies" connected for 48V. This has served me quite well (going on 10 years now)  and I'm getting very good battery life in general. I occasionally re-balance the batteries using a high-amp automotive tester and pair weak with good, etc. (if really weak I head to Walmart for another...)

I do independently charge the "buddies" so I am not using a 48V charger. 

However, in counter to the concern, I did find this article Parallel Batteries which seems to dismiss the concern. 

So...what say the gang? Dangerous? Or (within reason..) Safe? To save you a little reading, I've quoted the relevant section below:

"Curiously, (or perhaps not so,) reference 1 does not list plate shorts as a failure mechanism of deep cycle batteries. Cell shorts are a significant failure in starting and lighting batteries, but not in deep cycle batteries which use better plate separators. Cell shorts are possible, however, and as reference 2 points out on pages 30-31, cell shorts can occur when a cell has been allowed to selfdischarge too deeply and the lead sulfate become soluable enough to diffuse through the separator. A dendrite is then formed on recharge which conducts most of the current through the cell.
Cells which short rarely do so with a low resistance. A cell is made up of alternating negative and positive plates having an intervening separator. Shorts between adjacent plates, are usually a dendrite or a local failure of the separator. It's fortunate that cell shorts are not normally low resistance. Consider a 200 Amp hour cell. Suppose that the cell developed a short that allowed 100 Amps to flow. At that current, a 2 Volt cell would be producing 200 Watts of power across the short. A 200 Ah cell could support 100 Amps of current for about 30 minutes. During that 30 minutes, in excess of 340 Btu of heat would be generated. There is 25-40 pounds of active material in a 200 Ah cell, which will rise to the boiling temperature of water in about 10 minutes. The cell probably ceases to be a battery before boiling is reached. Assuming that it doesn't, we would have enough Btu left, (210), to boil about 1/2 cup of electrolyte. That's a lot of steam!
Obviously, if cells did short with a low resistance, batteries would be much more hazardous than they are. We'd have to mount batteries in special cases that could deal with the heat and acid steam. And given such dangers, there would be regulatory limits on the size of cells that could be manufactured. To get any reasonable capacity a large number of small cells would have to be paralleled. Hmmm.
As mentioned, a cell rarely, if ever, shorts with a low resistance. Some people would have us believe that a shorted cell in one battery of a multi-battery bank will cause a fire. The argument goes that the remaining batteries will rapidly discharge through the cells of the defective battery. Such huge discharge, the story continues, will create an inferno with batteries boiling like a Boston tea kettle, spewing hell infinitely in all directions. Battery cases will blow gaping holes in their sides leaving a rather untidy mess for the maid. It makes us want to wear our rain gear every time we inspect our batteries to find out if any unauthorized cold fusion experiments are occurring." 


[also...within a couple of months I may have some interesting news relevant to the industry..teaser...]

-Keith
 


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Posted by: oak <oak_box@yahoo.com>
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