[RE-wrenches] Odd battery problem - very low SG in only one cell

[Bill Loesch]

Hi Dan,

No definitive suggestions, but kudos for making it a learning experience 
for _all_. Great analytical technique. Hopefully you gain more 
credibility with the kids as a result of your candor.

Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094

On 11/22/2015 8:49 AM, Dan Fink wrote:
> Esteemed Wrenches;
>
> I'm looking for input on what could be going on with a battery bank at 
> the college I teach for. It's a stand-alone system with 4 Trojan 12v 
> T-1275 in series / parallel for 24v, 660w of PV, running only a 
> drainback solar hot water system for space heating. So, 3 pumps and 3 
> DTCs, max load 100 watts and doesn't run all that often, outback CC is 
> usually in float. The batteries are only 2.5 years old and are 
> regularly maintained.
>
> My lab class tested and maintained the battery bank last week, and on 
> one battery there was one cell, in the middle of the battery, with a 
> SG so low it wouldn't even register on our refractometer or midnite 
> hydrometer. That battery reads about 0.2v lower than the others. All 
> the other cells in that battery read reasonable SG, with 2 cells on 
> the downstream side reading SG slightly low, but still in reasonable 
> range. This was of course all before topping up the electrolyte with 
> distilled water.
>
> Our troubleshooting exercise looked at:
> ~ Measurement error? Nope, I was right there supervising and 2 
> different lab classes got the same results with 2 different instruments;
> ~ Stratification? A suspicion especially since the system is usually 
> in float. We equalized twice, no change in SG. I DID hear that likely 
> this was the first time the batteries had ever been equalized, but no 
> way to know for sure.
> ~ Spilled electrolyte from tipped battery replaced with water by a 
> previous instructor's class? Can't see this, all the other cells would 
> have lost electrolyte too;
> ~ A student accidentally discharged electrolyte into the bucket 
> instead of back in the cell, then was replaced by distilled water when 
> topping up? I can't see that either, the midnite hydrometer needs only 
> a small sample.
>
> So, I'm left with "likely we have a cell that is failing for some 
> reason" and students secretly smug that the professor is also stumped.
>
> Any ideas?
>
>
> Dan Fink
> Adjunct Professor, Ecotech Institute
> IREC Certified Instructor™ for:
> ~ PV Installation Professional
> ~ Small Wind Installer
> Executive Director, Buckville Energy
> NABCEP Accredited Continuing Education Providers™
> 970.672.4342 <tel:970.672.4342>
>
>
>
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