[RE-wrenches] Battery cell shorting

[R Ray Walters]

Hi Nathan;

I  agree that too many strings can cause problems, as you mentioned, but I've seen 2 major problems with single battery strings, too:
1) A single cell failure, or corroded connection takes the entire system out of commission.
2)  Most batteries do not have enough current to meet the surge demands of larger inverters. Voltage then sags, and low voltage shut downs occur when the batteries still have half their capacity left.

After many years trying out everything, I found 2 strings is the optimum compromise. Redundancy = Reliability

R. Walters
ray at solarray.com
Solar Engineer




On Oct 23, 2010, at 5:26 AM, solardude97 wrote:

> Daryl was right on the charge rates. What is not referenced is the configuration of the battery bank.
> Since it is a 24 volt system it could possibly have multiple series strings paralled together. There will always be imbalances in the individual strings resulting in higher resistance in one string than another. This tends to direct the charging current to a path of less resistance possibly resulting in an overcharge condition on another string. 
> It is always best to avoid parallel strings and try for a battery capacity and voltage option that allows a single series string. This is much easier to achieve by using a 48 volt inverter in most applications.
> Nathan Jones
> Power Source Solar
> Springfield, MO
> 417-827-0738
> 
> On Fri Oct 22nd, 2010 10:02 PM CDT Darryl Thayer wrote:
> 
>> All batteries have a maximum charge rate and that rate decreases as the batteries get charged.  Rapid charging shows up as swelling of the positive plate. Also the rapid charging will cause the plates both to flake off material and this falls to the bottom of the case eventually shorting the plates For good life the battery should not be charged any faster than C/10 or for a T105 about 20 amps. also rapid charging causes a lot of heat and again can effect cases and plates.  The rapid charging at the end of cycle is hard on plates.  After damage has started on a set of plates it seem to go down hill rapidly.  Note that rapid discharge does not have the same effect.  But solar batteries can not be charged rapidly and have good life.  The depth of discharge also effects battery life, 
>>  
>> Thes batteries should have a charge controller, 
>>  
>> I have a hermit that has lived on 8  Trojan T105s for over 5 years and when I tested them last summer they were still very capable.  They had about 70% of what they had when new.   
>> 
>> --- On Fri, 10/22/10, Kirk Herander, VSE <kirk at vtsolar.com> wrote:
>> 
>> 
>> From: Kirk Herander, VSE <kirk at vtsolar.com>
>> Subject: [RE-wrenches] Battery cell shorting
>> To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
>> Date: Friday, October 22, 2010, 2:39 PM
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> Hello,
>>  
>> I have an off-grid battery / generator / SW4024 system which has destroyed -3- sets of batteries in the last five years. By destroyed I mean multiple batteries having shorted cells, with electrolyte literally steaming out of them and bulging badly. The last two sets were Rolls T12-250’s. The first set was Trojan T105’s. This system has no solar, and I would not be surprised if the generator ran 10-12 hours a day charging the batteries, for the residents don’t believe in energy efficiency. I could see the batteries cycling to the point of being useless after a couple years, but the scary thing is the condition I’ve witnessed multiple times now. Any ideas as to why this has happened repeatedly across different brands of batteries? Thanks.
>>  
>> Kirk Herander
>> Vermont Solar Engineering
>> 802.863.1202
>> NABCEP(tm) Certified Solar Installer
>> NYSERDA-eligible Installer
>> VT Solar Incentive Program Partner
>>  
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