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
<tel:970..672.4342>970.672.4342
Â
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