> From: [email protected] > Date: Mon, 30 Dec 2013 10:03:49 -0500 > To: [email protected] > Subject: Re: [EVDL] Storing / charging LiFePO4
> weighed in... Why is 50% SOC a good thing for storage? As I understand it > a higher charge state is only a problem if you are pushing up above 3.8V > per cell and then they potential is breaking up the cell materials just - And breaking down, the electrolyte. (Jukka, correct me if Im wrong about this) So if the charger stay long total periods at high voltages, (som kind of constant "float" charge to the top end of the chargecurve,, that would be a bad thing to do, as I understand it _today_.. :-) > sitting there. And the major problem is the excess heat when you make that > high charge state. - As I understand it today, the heat hurt electrolytes, but I can be wrong about this. > The thermal expansion starts to break up the particles > of LiFePO4. 3.8V per cell is well above the flat voltage part of the > charge curve. > > What is bad about a low SOC? I hear about cells coming back from very near > zero just fine. - I dont think it is bad to be at 50-60% DOD, actually prefered I guess. Any Lower than 60% DOD, ..I dont know. But Deep discharges always seems to hurt cyclelife, (in a multi-cycling application) but that might be a true "mechanical" thing(??) If so it _might_ not be a problem if they just sit still and do nothing even if we are at low 95% DOD.. "Maybe" But why take the chance? :-) Also it might be a grater risk of other handling errors/problems? For example if they start at a bottom balanced level, and then the customer forget about them.., Maybe some small self discharge over the years and so on.. Or it might be connected to something, or just dirty. Anyway, it will not be a good thing to do. :-) // John > > > On Sun, Dec 29, 2013 at 5:38 PM, J Bills <[email protected]> wrote: > > > yes, certainly freakish when you're used to lead! > > > > and to be clear - they haven't "dropped" .05 - they were .05v range from > > one another. As far as I know, they didn't budge an inch that whole year > > and a half - they were "around" 3.3 when I brought them home and remained > > right there. If they'd have been dropping noticeably, I might have > > considered charging. > > > > Just saying my experience was that they were perfectly fine when stored - > > YMMV and there are certainly lots of time consuming ways to measure 45 > > cells to see how they're holding up while being stored, but that wouldn't > > necessarily change the fact that they're being stored and will continue to > > be stored. End result is all that matters. > > > > > > On Sun, Dec 29, 2013 at 6:42 AM, Michael Ross <[email protected] > > >wrote: > > > > > Freakish, eh? How much does the state of charge change with a variation > > of > > > 0.05V on a LiFePO4 cell? > > > > > > Estimating say 90% of the SOC lies between 3.2 and 3.4 (0.2V of change). > > > 0.1V = 45%, 0.01 = 4.5% then a variation of 0.05V on a cell could be a > > SOC > > > variation of 22.5%. > > > > > > So a variation of 1mV could be half a percernt. Some of inaccuracy could > > > be from the instrument itself as inexpensive DMMs may not be really good > > at > > > measuring a single millivolt. > > > > > > I am just estimating, but I don't think that 0.05V change is necessarily > > > "rock solid." > > > > > > Voltage is just a crapulous way to measure SOC on LiFePO4 cells. > > > > > > > > > On Sun, Dec 29, 2013 at 4:16 AM, J Bills <[email protected]> wrote: > > > > > > > Totally. I'm not necessarily proud of it, but my 144v pack of lifepo4 > > > must > > > > have sat there for at least a year and a half and was rock solid 3.3v > > > much > > > > across the board the whole time, same as when I brought the crates > > home. > > > > All within .05v of each other. > > > > Almost freakish! > > > > > > > > early days on that project, I went ahead and picked up a single cell > > > > lithium charger off of ebay for like $20 - I want to say it was 6A and > > I > > > > remember the cutoff wasn't great but not too bad, might have been 3.8v? > > > I > > > > mean, don't quote me, never needed to use it, but just saying they are > > > out > > > > there and cheap. > > > > > > > > > > > > -- > > > 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/20131229/9e3252f2/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) > > > > > > > > > > > -------------- next part -------------- > > An HTML attachment was scrubbed... > > URL: < > > http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20131229/00e3d052/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) > > > > > > > -- > 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/20131230/6bc13176/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) > -------------- next part -------------- An HTML attachment was scrubbed... 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