T-Pain Is On A Boat: 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