Lots of great info on this thread! I was actually revisiting the literature on this recently myself. Although my 914 is garaged for the winter, it happens to be at home this year (with its transmission in pieces), and I wanted to top off the battery in case we lost power in all the crazy weather we've had up here in the Northeast -- I figured it could probably run my fireplace insert for several days. Ultimately, I decided it wasn't worth the risk.
I would avoid charging below 5 degrees C if at all possible (to account for measurement error, etc), and if you must charge, do so at very low rates (C/20) and stay away from 100% SoC. It is really hard to find good literature on exactly what's tolerable for existing technology -- most seems to be examining novel electrolyte formulations; generally, I gather that some charge acceptance is possible below 0, but it's very limited, and it gets worse as the cell approaches full. If you have an ICE, suck it up & burn some gas when the weather is this nasty. If you must drive your EV all winter, consider battery heaters or a space heater in your garage. I think the jury is out on whether or not lithium plating also presents a safety issue, but I for one don't want to take any chances. I've heard rumors of A123's having good low-temperature charge performance, but I wouldn't assume that extends to CALB -- it may have more to do with the nanoparticles and ridiculous rate capability than the electrolyte or chemistry. While we're at it, if you're even at 5 degrees, you should be limiting your charge rates. Ion mobility is not a step function! Lithium plating happens when you apply more charge current than the cell can accept; if the cell, or even a localized portion of the cell, is saturated, its voltage rises and lithium is deposited on the anode. The same thing would happen even at 25C if your charge rate were high enough. For what it's worth, my Tesla is extremely stingy about low-temperature charging; it won't apply any charge current until it has warmed the battery and it starts limiting charge and regen currents at temps as high as ~50F (10C). Given their close relationship with Panasonic and the effort they've put into maximizing both battery life and usability, I have to imagine that if charging below freezing could be done safely they'd be doing it. Maybe someone ambitious and willing to burn some cash could try some experiments for us. Lithium plating leaves a discernible voltage signature in the cell's discharge curve, in which the voltage during the first portion of the curve is inflated, then falls back to normal partway through the cycle. Buying several CALB cells, instrumenting them with good equipment, and testing them for several cycles each at various temperatures/charge rates would probably be sufficient to determine where the threshold of plating lies; then a little conservative extrapolation will give us a safe operating area. Not really an option for me even if I had the money, since my cells are ThunderSky and can't be bought anymore. Example voltage curve http://jes.ecsdl.org/content/158/4/A379/F13.large.jpg (the full article is paywalled but google takes you to the image). -Ben On Feb 23, 2015, at 1:38 PM, Michael Ross via EV <[email protected]> wrote: > Christopher, > > This is going to be different for every anode chemistry and electrolyte > package. Now that reliable shorter time interval testing is possible, we > may start to see better information like you are asking for. I think you > are stuck with being careful and not really knowing. Heat your pack when > charging below freezing - certainly, absolutely, below 0°F. YMMV. > > I would guess C/10 might be OK, based on nothing at all. > > Start pushing the people you buy cells from to get good testing done - or > else you will buy from someone who does do it. That is the only way it > happens. > > Mike > > On Mon, Feb 23, 2015 at 10:15 AM, Christopher Darilek via EV < > [email protected]> wrote: > >> I've heard this same thing but was not clear on how low of a rate. Does >> anyone know? Around C/10? Or lower? >> -ChrisChris' 1972 BMW 2002 >> >> | | >> | | | | | | | | >> | Chris' 1972 BMW 2002Owner Chris Darilek Location Austin, Texas US map >> Web WebPage Vehicle 1972 BMW 2002 Motor Advanced DC Series Wound DC >> Drivetrain 9" motor, standard ... | >> | | >> | View on evalbum.com | Preview by Yahoo | >> | | >> | | >> >> > -- > 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 > > [email protected] > <[email protected]> > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <http://lists.evdl.org/private.cgi/ev-evdl.org/attachments/20150223/297a8800/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) > _______________________________________________ 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)
