Indeed! I believe low charging voltages are, at least in part, responsible for LiFePO4's amazing calendar/cycle life. Also, I am told Tesla's Model S gives owners the option to charge conservatively, for life at the expense of range, or aggressively for a long trip. Another part of Tesla's secret is that the pack is so large that C rates are kept low, as is DoD for most drives. That, and you don't need many cycles at 265 miles each to hit 100k miles...
I am curious, though: what do the real world results say from people driving homemade EVs? ThunderSky has been around for a while now; even CALB has been around a few years. I haven't noticed many posts about people replacing lithium packs and it's hard to get a feel browsing the EV album how many miles people are putting on their lithiums. So, how many miles have people gotten out of their packs? Are any outright dying? Maybe we could compile a database and make some graphs like that excellent pluginamerica link? I don't have significant data yet, but I'll go first, as an example: Pack: 54 ThunderSky 100Ah Age: 3yrs (bought June 2010), in service since March 2012 Miles Driven: 5000 Capacity remaining: unknown* but have hit 80% DoD several times without issue Top charge voltage: 3.6V BMS used: yes, custom Temperature Management: no Location: Massachusetts *one cell was over-discharged last winter after ~2000 miles. During recovery, it accepted 103Ah to 3.6V @ 5A (+/- maybe 5%?). It has sat idle since... Cheers! -Ben On Oct 8, 2013, at 7:25 PM, Cor van de Water wrote: > I posted in the past a spec how end charge voltage affects cycle life. > There are numerous complaints from laptop owners whose battery failed > just after the 1-year warranty, so most likely they never got more than > 100-200 cycles (which is marginal lead-acid type performance) > and it appears that laptops tend to charge their cells to 4.2-4.3V wich > indeed significantly reduces their life, but giving highest capacity. > Lowering the final charge voltage to 4.1 alone will sacrifice some > capacity > but multiply (!) the cycle life by 2 or 3. > So, I am quite sure that EV manufacturers do not charge their packs > to the brim and by staying well away from that bleeding edge, give their > packs a much longer and much happier life - even if they use the same > technology as consumer cells... > (but since we have been able to read here how Tesla deviates from > standard cells, we know that they get special variants and they have the > volume to make demands...) > > Regards, > > Cor van de Water > Chief Scientist > Proxim Wireless Corporation http://www.proxim.com > Email: cwa...@proxim.com Private: http://www.cvandewater.info > Skype: cor_van_de_water Tel: +1 408 383 7626 _______________________________________________ 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)
