From: corbin dunn <[email protected]> Hi steve, <Can you do a capacity test of the two bad cells you took out?> One is totally zero. and the other, according to the customer, was dropping out at about 230ah, I believe this is I heard. The other problem is... this one would turn OFF the Charger. An interesting thing happened when I was charging the two replacement batteries. I had them in Parallel, trickle charging them at 3amps for days. When I put them in the car, and charged the pack, including the new ones, one of the new ones did not come up to 3.6V which is where the regulators have the red and green light ON. So I hooked my little power supply up to the one battery and it took 2 days for him to come up to the 3.65V that the regulators show those lights ON. This means, that even though the 2 batteries were charged in Parallel, for days, one was approximately 50ah behind the other.
<How many miles did the guy get before the two cells failed?> almost 40,000. these are not the first cells to have failed. I believe there were 2 others the years before. Of course when we say "failed" here, we are talking about under 260ah. <How much time?> 5 years. <What is the BMS settings for min voltage (discharge) and max voltage (charging)?> Min. buzzer is: 2.7v and Max red/green lights lit: 3.6v I believe the charger is told to shut OFF at 3.7V <What model TS cells?> These are the yellow with the Blue / red button in the center. Probably what ever was popular 5 years ago. Originally, the charger was set for 45 cells. My customer decided to put 3 extra cells in, to cut back on the aggressive charging. The Charger now will sit at .2amps and not have the regulators force the charger to stop charging. The process of leaving the charger ON until all red/green lights on the mini BMS is lit is done about once a month, I believe. He has a collection of charger, which when all are plugged in, put out about 70amps. After doing the capacity test, I charged the pack back with the small 12amp charger. I will check today to see that all red/green lights come ON. I would like to do one more capacity test while I am here ( off the clock). To see if there is any difference. The more opportunity I get to play with these batteries, the more that I am seeing that they are not like Lead Acid Batteries. One problem with them that I see, is that if you have ONE cell whose resistance is higher than the others, the BMS will start shunting current on that one cell, giving him less ah. As this process continues cycle after cycle, that one cell ends up with less ah than the rest. Which means on the discharge, he is that much closer to the critical area than the rest. So he starts to heat up more than the others. This in turn, makes his two friends on either side of him... a little warmer. It seems that the cells usually go out in pairs or in 3's.. And my guess is that the Center one is the stinker and the two on either side take the heat. Steve Clunn I replaced a 200ah Thundersky cell after ~20,000 miles / 2(ish) years. Its capacity loss was about 30% (off the top of my head -- I can find the actual number if someone wants to know) corbin -- Steve Clunn Merging the best of the past with the best of the future. www.Greenshedconversions.com _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
