<div dir="ltr">Thanks everyone for the replies and ideas both on and off list.<div><br><div>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.<br><div>Best regards and thanks again;</div></div></div><div class="gmail_extra"><br clear="all"><div><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div><div dir="ltr"><div><span style="font-size:12.8000001907349px">Dan Fink</span><div style="font-size:12.8000001907349px">Adjunct Professor, Ecotech Institute</div><div style="font-size:12.8000001907349px">IREC Certified Instructor\u2122 for: </div><div style="font-size:12.8000001907349px">~ PV Installation Professional</div><div style="font-size:12.8000001907349px">~ Small Wind Installer</div><div style="font-size:12.8000001907349px">Executive Director, Buckville Energy</div><div style="font-size:12.8000001907349px">NABCEP Accredited Continuing Education Providers\u2122<br><a href="tel:970.672.4342" value="+19706724342" style="color:rgb(17,85,204)" target="_blank">970.672.4342</a></div><br> </div></div></div></div></div></div></div></div>
<br><div class="gmail_quote">On Tue, Nov 24, 2015 at 7:30 AM, Drake <span dir="ltr"><<a href="mailto:drake.chamberlin@redwoodalliance.org" target="_blank">drake.chamberlin@redwoodalliance.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
Having one cell die seems to be an emerging pattern.<span class=""><br><br>
<br>
At 09:49 AM 11/22/2015, you wrote:<br>
</span><blockquote type="cite"><span class="">Esteemed Wrenches;<br><br>
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.<br><br>
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.<br><br>
Our troubleshooting exercise looked at:<br>
~ Measurement error? Nope, I was right there supervising and 2 different
lab classes got the same results with 2 different instruments;<br>
~ 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.<br>
~ 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;<br>
~ 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.<br><br>
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.<br><br>
Any ideas?<br><br>
<br>
Dan Fink<br>
Adjunct Professor, Ecotech Institute<br></span>
IREC Certified Instructor\u2122 forr:Â <br><span class="">
~ PV Installation Professional<br>
~ Small Wind Installer<br>
Executive Director, Buckville Energy<br>
NABCEP Accredited Continuing Education Providers\u2122<br>
<a href="tel:970..672.4342" target="_blank">970.672.4342</a><br><br></span>
 <br><span class="">
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