I suspect I probably have higher resistance on these two cells, but I haven't done anything to try and measure it. When weather is cold and currents are high, I get low-voltage alerts from the BMS. I am sure that these two cells are the most likely to be the source of the low-voltage alert.
The cells seem to charge up OK and the charger is smart enough to terminate charge properly. The MiniBMS is still present to shut off the charger if it tries to overcharge a cell. Mike > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Lee Hart > Sent: Saturday, March 02, 2013 10:26 PM > To: Electric Vehicle Discussion List > Subject: Re: [EVDL] LiFePO4 over-discharge threshold > > On 3/2/2013 9:52 PM, Mike Nickerson wrote: > > 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 have found that while they seemed to recover, their internal resistance > had gone up. In the case of one cell, it went up a LOT (like > 4 times its initial value). This caused excessive voltage drop under load, and > its voltage would rise too quickly on charge. > > A cell that is damaged like this is an ideal setup to cause a disaster if the EV > doesn't have a BMS. > > -- > I do not waste my life in friction when it could be turned into momentum. -- > Frances Willard > -- > Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm > _______________________________________________ > 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)
