On 6 Mar 2014 at 20:01, Michael Ross wrote: > Do you think if LiFePO4 are BB'd and limited to operating between 20% and > 80%, or 10% and 90% SOC that they will have degraded cycle life?
I'm guessing that by "BB" you mean "bottom balanced." Yes? Sorry, I don't have the experience to answer this question. I'm sure someone else will tackle it, though. It does seem to me that there's still a fair bit of varying opinion among hobbyists on how to charge LiFePO4s. No surprise; it's still pretty new technology. Heck, there are still plenty of differences among us about charging AGM lead batteries and even flooded batteries. I suppose that somewhat more definitive answers will emerge as time goes on, though, just as they have for lead batteries. My poorly-informed view of bottom balancing is that I'd better not try it. I get the impression that it takes more time and attention than I care to give to charging batteries. Not that I want to sound cavalier or anything, but dang it, I have too many other things I like doing! Without a smart BMS looking after my battery, I'd probably murder it. What little personal experience I have with lithium is based entirely on Ping's bike/scooter batteries. They come pre-configured with a charger and BMS - wire 'em up and go. While they're not suited to a high-power EV, at a fairly reasonable (IMO) cost, they're about as close to idiot-proof as you'll find. They're 24v nominal. I run them until they fall to about 20-21v under load. (I read in one of the Ebike forums that 2.5 vpc is a good place to stop.) This is actually pretty convenient, because 21v under load (1.75 vpc) is where I'd stop using a 24v lead battery anyway. This gives me a little margin of error. So, when they hit 20-21v, I charge. On most cycles, I try to manually stop the charger when the first BMS cell light goes on. However, as I say, I tend to do other things while charging, so I miss that light fairly often. I just consider that an opportunity to top-balance them. ;-) So far I'm pleased with the results I'm getting. I see no loss of capacity after 2+ years. (Probably not more than 100-150 cycles, though.) Based on my experience to date, if I were to put LiFePO4 in a road EV, I'd probably look for a BMS similar to the one Ping uses. I appreciate its "idiot-proofness." As always, your mileage may vary. David Roden EVDL Administrator http://www.evdl.org/ _______________________________________________ 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)
