<div dir="ltr">Esteemed Wrenches;<div><br><div>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.</div><div><br></div><div>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.</div><div><br></div><div>Our troubleshooting exercise looked at:</div><div>~ Measurement error? Nope, I was right there supervising and 2 different lab classes got the same results with 2 different instruments;</div><div>~ 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.</div><div>~ 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;</div><div>~ 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.</div><div><br></div><div>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.</div><div><br></div><div>Any ideas?</div><div><br></div><div><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>
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