Bill wrote: "I think it is important to not group all Li-ion in the same basket."
And that is the right answer. Ask your cell manufacturer for the specifications. Joggling with the electrolyte mixtures is what people do so you really cannot say anything generic. For sure it's better for the cell to have it in the optimal temperature range which usually is about 25C +/-5C. It's not that big deal to give the battery box a light layer of insulation. Ventilation and heating help more and they are not too hard to make either. -Jukka http://www.google.com/profiles/jarviju#about 2015-02-24 7:50 GMT+02:00 Bill Dube via EV <[email protected]>: > Does the data presented apply to Li-Fe-PO4 or only to Li-Ion metal oxide? > I know that they have a distinctly different chemistry than metal oxide > cells, and I know that they have different charging characteristics. It is > likely they have different cold weather charging behavior as well. > > I looked up a few references on the web and you seem to be able to charge > LiFePO4 cells down to -10 C quite normally with no caution mentioned about > going to lower temperatures. An example is Powerstream Batteries < > http://www.powerstream.com/LLLF.htm> show in their specifications charge > down to -40 C. The A123 cells spec sheet show a temperature range of 55 to > -30 C. I don't see any reference to lithium plating out or anything drastic > when I restrict my search to LiFePO4. ( I also ignored blogs and forums. I > just looked up papers and manufacturer specs.) I think that cold weather > effect may be restricted to lithium-ion "metal oxide" cells. > > That reflects my personal experience with a pack of LiFePO4 ThunderSky > cells in freezing Colorado weather with outdoor storage. The vehicle took a > few miles to warm up the pack, and range suffered a bit because of voltage > sag due to cold weather, but that was about the extent of it. > > I think it is important to not group all Li-ion in the same basket. The > LiFePO4 cells share a few of the characteristics with metal-oxide cells, > but are quite distinct in many ways. Also, there are a great variety of > metal oxide li-ion cells, which are distinct from each other. > > Bill Dube' > > > > On 2/23/2015 5:19 PM, Michael Ross via EV wrote: > >> Discharging pulls lithium off of the cathode side SEI (solid electrolyte >> interface) if it has been plated there, but according to the >> electrochemists other bad stuff goes on so the capacity lost to plating >> the >> cathode is not reversible even if the plating itself is reversible. >> >> I wish I understood this better, but the science of it may be uncertain >> beyond knowing that it is bad. >> >> So when you charge, the ions move towards the cathode, and when it is cold >> the motion into the cathode is too slow and the lithium piles up on the >> SEI >> as a metallic lithium - it is plated. >> >> When you discharge the metallic lithium diffuses into the electrolyte and >> the motion of ions is towards the anode. >> >> I am not aware that discharging is a problem, I have seen nothing in the >> literature about it; and high currents will generate heat right where the >> action is. >> >> On Mon, Feb 23, 2015 at 2:11 PM, Rick Beebe via EV <[email protected]> >> wrote: >> >> That was one of my big concerns when I built my truck so I tried to fix >>> it >>> from the beginning. I put 1" of foam insulation in all my battery boxes. >>> I >>> installed battery warmers under the batteries. I used 35 watt Farnum >>> heaters I got from KTA-EV. And I built a controller to turn the heaters >>> on >>> below 15C and to disable charging below 3C. All of that runs only when >>> the >>> truck is plugged in. >>> >>> I've been leaving the truck plugged in at home and it's keeping the >>> batteries at 15C (60F) despite temps to -20C. CALB allows the cells to be >>> discharged at a much lower temperature than charging so I'm less worried >>> about the cells cooling off with the truck unplugged at work. That said, >>> the insulation really helps slow down that process. I've found that on a >>> 20F day the cells have dropped to about 45F after 8 hours at work. The >>> other advantage to the cells being warmer, of course, is much better >>> performance. >>> >>> My understanding is that temperature of the anode is the critical piece. >>> I >>> don't know if your BMS is measuring that or simply the air above the >>> cell. >>> >>> --Rick >>> >>> On 02/20/2015 03:25 PM, Danpatgal via EV wrote: >>> >>> Reviving this thread as we're having another very cold stretch here in >>>> the >>>> Eastern US. >>>> >>>> My batteries (SE130 CALBs) are still going, but boy do they sag when >>>> it's >>>> cold like this. It's annoying. >>>> >>>> I've been charging when my BMS sensors (atop each cell) are over 0C, >>>> which >>>> they have generally remained over the past few weeks despite the cold >>>> (thankfully my garage generally stays above 0C). >>>> >>>> But, my follow-up question on all this is if the BMS measurement is good >>>> enough. For example, I guess there is resistive heat that gets >>>> generated >>>> upon charge/discharge/shunting that probably make the sensors read >>>> higher >>>> than the cells themselves. How much, I don't know. >>>> >>>> Does anybody have any thoughts, experience on this? We've gotten down >>>> to >>>> -20C with a HIGH today of only -10C ... yet I'm charging. I didn't >>>> really >>>> want to do it, but I was dragging so much on the road with low SOC%, I >>>> had >>>> to, or risk having to really limp home. >>>> >>>> _______________________________________________ >>>> >>> 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/20150223/6652c485/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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