If one cell gets a higher internal loss than the others is hogs the charging
current and will over charge its string partners. It is a problem of the
temperature of all cells in all parallel strings having the same thermal
environment, so they all have the same voltage. (the case of one of 4 parallel
strings in battery house, big system, the string near the outside south wall
caught fire) In particular this is a problem of AGMs, a recent east cost
problem where batteries had been in business for 2 yrs and for some reason the
battery room erupted with one of 5 strings in thermal runaway. this is the
same as trying to put bipolar transistors in parallel.
I reciently had 8 parallel strings not of my choice, advised customer of
potential hazard, used Midnight combiner with 30 amp breakers on each string,
so far it is OK but this is playing with fire. Hopfully if one string goes bad
in thermal runaway it will trip the breaker feeding that string. .
________________________________
From: boB Gudgel <b...@midnitesolar.com>
To: RE-wrenches <re-wrenches@lists.re-wrenches.org>
Sent: Wednesday, June 1, 2011 1:16 AM
Subject: Re: [RE-wrenches] 24 volt Battery Bank comparison
OK, I've been hearing for years now that one battery string is best
and maybe two but no more should be used.
What is the reason for this fear ??? What is the experience with
multiple strings in parallel ??
If it is because of current sharing of the strings, that shouldn't
be an insurmountable problem if the wiring is done right.
If it has to do with the possibility of fire, which Darryl
mentioned, seems that series string fuses could mitigate the
possibility of that issue, if because of shorted cells, just like PV
combiners.
Or maybe it has to do with the trouble of getting into the middle of
a pile of batteries ? Use battery boxes ?
The strings are in parallel and so they all get the same voltage,
theoretically anyway if the connections are good.
I would think that the more strings, the LESS stress on individual
batteries, not more. The current in each battery should be less
than it would be I would think.
So what is the real experience ??
Is a battery balancer the answer ??
Thanks,
boB
>On May 31, 2011, at 8:23 PM, "Wayne Irwin" <wa...@pureenergysolar.com> wrote:
>
>
>I think the verdict is12 - Rolls 2-YS-31 2430 AH @ 20 HR (one string) and one
>dry spare in storage is the best case scenario!
>>
>>Wayne Irwin, EE
>>Director of Engineering
>>Pure Energy Solar International Inc.
>>State Licensed Solar Contractor
>>License # CVC56695
>>wa...@pureenergysolar.com
>>http://pureenergysolar.com
>>352 377-6527 Office
>>352 336-3299 Fax
>>352 316-1637 Cell
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