Dave, Thanks for the no BS answer. Very respectable.
I gather that bottom balancing depends on cells that don't self discharge - not the thing at all for PbSO4. There is little charge left in LFP cells above and below the flat voltage region that is so pronounced. I think 2.5V is a reasonable choice. On the high side above 3.5V very little more can be stored in them. Anyway, I think I will try it. I don't have a BMS for my salvaged pack. And buying a low cost one from China means you know almost nothing about its function before confirming a payment. Then there is the question of quality and it is one more thing to fail on the road. So there is an appeal to bottom balancing in terms of life, cost (ignoring labor, but we are DIY'ing so that is ignored always), and ease of use. Best, M On Fri, Mar 7, 2014 at 12:43 AM, EVDL Administrator <[email protected]> wrote: > 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) > > -- Put this question to yourself: should I use everyone else to attain happiness, or should I help others gain happiness? *Dalai Lama * Tell me what it is you plan to do With your one wild and precious life? Mary Oliver, "The summer day." To invent, you need a good imagination and a pile of junk. Thomas A. Edison<http://www.brainyquote.com/quotes/quotes/t/thomasaed125362.html> A public-opinion poll is no substitute for thought. *Warren Buffet* Michael E. Ross (919) 550-2430 Land (919) 576-0824 <https://www.google.com/voice/b/0?pli=1#phones> Google Phone (919) 631-1451 Cell (919) 513-0418 Desk [email protected] <[email protected]> -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20140307/445f323d/attachment.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)
