On Fri, Oct 18, 2013 at 1:27 AM, Martin WINLOW <[email protected]> wrote: > > You MUST use a BMMS if you go with lithium - some will say you don't but > £kkk's is a lot of money to lose if you cook your battey pack due to > overcharging it or kill one or more cells over-discharging it. If it's > parked in your garage being over-charged, you could lose that too! A good > one would be about £6-700 depending on how many cells you have. >
This is definitely something you will want to thoroughly research your self. There are many different variables in how people have treated LiFePO4 prismatic cells. Without accurate details it is difficult to know what killed a battery. There are cases where a BMS system killed some or all of a pack and cases where it didn't. There are cases of systems without a BMS which had battery failure so the assumption was that a BMS would have prevented the issue. That is not necessarily the case! I was told by some people on this list that if I didn't have a cell level BMS on my pack that it would drift out of balance very quickly and I would kill a battery. Well, that hasn't happened to me in the past 27 months of no balancing. Also, John Hardy in the UK posted at http://blog.evtv.me/2013/10/das-boot/#comment-11955 "I now have 900 cycles on the original 8 cell pack of CALB40s. Voltage variance has DROPPED from 28mV at cycle 50 to about 6mV for the last 100 cycles or so with no active or passive balancing." This is why you need to do your own research on this matter to determine really what you are willing to live with. There are several accounts of people who had left some sort of parasitic load on their EV and parked it for an extended period of time only to come back with a pack of LiFePO4 cells at extremely low voltages, some less than a volt. Because they bottom balanced their packs they did not lose any cells. Again, do your homework. David D. Nelson http://evalbum.com/1328 http://www.levforum.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)
