Hi Ben, I once took two ThunderSky cells to 0 volts and was able to recover them both. I drove further than I should and had a pack that was rather severely out of balance without realizing it. I charged them carefully with fans on them to keep them cool. I expect they are still my weakest cells, but they are still running in my car two years later.
I think you are probably OK having caught the cells while still above 1V. I would suggest changing out the BMS module causing problems before it does something else. I have kept my MiniBMS modules on my pack while having it split for the winter before. My only problem was the cells where the MiniBMS had intermittent contact and wouldn't draw down the cells as much as the others. That left the pack slightly unbalanced. I fixed that with a small RC charger to balance the cells. Mike > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Ben Apollonio > Sent: Saturday, March 02, 2013 6:38 PM > To: Electric Vehicle Discussion List > Subject: [EVDL] LiFePO4 over-discharge threshold > > Does anyone know the 'do not go below' voltage at which the anode starts to > break down in LiFePO4? I know it's somewhere at or below 2.0V but that's > about all. > > My car is parked for the winter. The other day, I went to fire it up & check on > the batteries and my BMS refused to unlock it. Some investigation revealed > that one of my ThunderSky cells was at 1.16V! (the rest were all at 3.345V). It > may have been at that level for weeks or only hours, I really have no idea. > So, after kicking myself for not disconnecting the BMS when I took the car off > the road, I disconnected everything (I once before saw this particular module > spontaneously turn on a balance resistor, but after several months without > incident I thought I'd fixed the cause). Today I came out to remove the cell > from the pack and discovered that it had recovered to 2.245V! It may have > helped that temperatures have been pretty cold here in New England. I'm > gently trying to nurse it back to health in an isolated area with a close eye on > voltage, temperature, and amp-hours, but I'd want to understand the > chemistry better before I felt comfortable putting it back in the ca r. > > I tried looking around the EVDL archives and the internet but couldn't turn up > any numbers on the cell chemistry. What's the voltage below which actual > damage occurs? Does the fact that the voltage recovered mean that it was > not, in fact, over-discharged? Or does it just mean that with things > disconnected the chemistry stabilized at some minimal potential? > > Thanks in advance, > -Ben > _______________________________________________ > 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) _______________________________________________ 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)
