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

[Tump]

Batteries will fail, 2 volt cells are easily replaced your, not so w/your 12 volt cell, thats the whole battery. What causes it? usually its a manufacture issue. bad weld on the plates, poor forming of the plates in the cell. I have seen this many times where there IS voltage but no Spg. You were correct to try and EQ  (low input current / hi voltage for a few days until the other cells reach the manu's recommended specs)but as you saw there was no change... so its a bad battery. Keeping good records w/ a good refractomter is critical and quite helpful when confronting the manufacture for replacment. In your application I would not hesitate to install a single replacement battery. Non critical & certainly very little cycling. Tump
On Nov 22, 2015, at 10:08 AM, Jay wrote:

> Hi dan
> 
> Assuming all charge settings correct, it's a manufacturing fault. 
> I couldn't tell if the other lower SG readings were in the same battery or not. 
> 
> I just replaced a 1 yr old HUP, cell. 
> 
> Now as to what, why, how it failed, that's a good mystery
> 
> Jay
> 
> 
> 
> 
> 
> On Nov 22, 2015, at 6:49 AM, Dan Fink <danbob88 at gmail.com> 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
>> 
>>  
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