Philip, Another problem may be a bad connection between the cells, so that a cell voltage is seen including the drop in the wire. But yeah, you can have a bad cell as well, a quick way to check is to watch what the BMS says during driving - does the bad cell also drop quickly? Another way to check if the BMS or the cell is a problem is to swap two cells and re-connect the wires and BMS in the same way so the cell is in a different spot according the BMS. Success! Cor.
-----Original Message----- From: EV [mailto:ev-boun...@lists.evdl.org] On Behalf Of rash via EV Sent: Monday, February 05, 2018 7:21 PM To: ev@lists.evdl.org Cc: rash Subject: [EVDL] suspicious of a bad calb cell? Hello, I recently upgraded my lead-acid EV conversion to lithium, specifically 46 CALB 72Ah cells. I've been conservative in my bms settings, not allowing any cell to go above 3.55V or below 2.6V (hopefully "conservative" limits with calb-published limits of 3.65 and 2.5 respectively). I took care when I got the batteries to balance them; I've also been careful to not charge when the temp is below 0C. I've been driving with them for about a month now and have been really happy with the results so far (especially after shedding over a kilopound of battery weight!) But just this week I've become suspicious of one particular cell: now during charging its voltage rises significantly faster than the other cells, and of course once it reaches 3.55V, my charger pauses/ turns off, meaning the other cells don't get as much charge as intended. Then all the cells find a "resting voltage" nearly equal to each other (including the suspect cell). But of course once charging resumes, the one cell still rises faster than the rest. Today I've had some luck turning down the current on the charger enough so that the shunting in the BMS can (mostly) keep up, allowing the remaining cells to charge. (Though this means of course that charging is taking much longer.) Is this a sign I got a bad cell? I also have a PowerLab8 (that I haven't used in a long time), so I may experiment with it when I get some time later in the week... These cells should still be under warranty, so I can explore that route, but thought I'd get some feedback here first; thanks! Philip Rash http://www.evalbum.com/3381 -- Sent from: http://electric-vehicle-discussion-list.413529.n4.nabble.com/ _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA) _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
