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

[Dan Fink]

Thanks everyone for the replies and ideas both on and off list.

Based on your input, next week when the system is in Float I plan to have
the class isolate the faulty battery and measure voltage, let it rest for a
couple days, then load test at about C/10. Predicted result is that it will
show extremely low amp-hour capacity. Since the other battery in the string
will then be isolated also, we will load test it at the same time to
compare.
Best regards and thanks again;

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



On Tue, Nov 24, 2015 at 7:30 AM, Drake <drake.chamberlin at redwoodalliance.org
> wrote:

> Having one cell die seems to be an emerging pattern.
>
>
> At 09:49 AM 11/22/2015, you 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™ forr:Â
> ~ PV Installation Professional
> ~ Small Wind Installer
> Executive Director, Buckville Energy
> NABCEP Accredited Continuing Education Providers™
> 970.672.4342 <970..672.4342>
>
> Â
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