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Lithium Battery Failure Info

3K views 9 replies 6 participants last post by  MN Driver 
#1 ·
#3 ·
I have read that if you have just taken your pack off of the charger, then you are good to go as the internal temp. is high enough if the car was inside over night.

Where I live here in central AZ, this sounds reasonable. Especially that my battery boxes are sealed and insulated.

Elsewhere where it actually has a winter, it might require a box heater.

Miz
 
#5 ·
To ease my mind regardign lithium plating, I conducted a week long of testing at sub-zero temperatures (-8 to 0C) to see what happends with the cell.

Cell used was a HW38140, 12Ah cylindrical cell, fresh from box new from 2011 ~ juni
Charging current 2.3A (matches the current the cells will see in my pack during charging)
Charge cut off 3.5V
Discharging current 8.5A (matches 50mph cruise power)
Discharge cutoff 2.8V

Start of the week,
the internal impedance was measured @ empty @ 15C at 8mOhm.
Capacity was ~ 11300mAh

End of the week
the internal impedance was measured @ empty @ 15C at 8mOhm.
the capacity was was within ~100mAh of first measurement.

The only test remaining is pressing a nail through to cell to see if it became dangerous.
 
#8 ·
I missed that line at the top of the graph.:eek: I wonder how they can say that on one graph and say that the safe window goes below 0°C in another? I also wonder what effect the charging rate has on plating at the lower temperatures. I typically charge at ~14A which is only 0.07C for my 200Ah pack. I would assume that since the charge rate is so low that this would minimize lithium plating at lower temperatures.
 
#9 ·
About that graph. Even if that graph represent a large portion of the truth about the window of operation for Lithium Iron Phosphate cells. that graph looks awfully lot like someone had spare time with a bitmap editor like MS Paint. Makes me mildly annoyed / worried about publishing data like this.

Is there no factual test data for low temperature charging of Lithium Iron cells anywhere on the 'interweb'?
 
#10 ·
Outside of gottdi's posts here where he used dry ice and found out how cold they need to be before they produce no current at all, no we haven't found the data and when people ask about it from the manufacturers directly we basically get whoever these guys hired to translate(poorly) to English to read us what the specsheet says and any further questions go unanswered no matter how we seem to ask them. I've been in contact with two different manufacturers and a US distributor of cells that I've been interested in and this question is usually directing back to the specsheet, 'we tested them to our specsheet, outside that buy them and see', or something vague similar to 'our cells do many great things for your pleasure while driving car'. Umm, yeah. I've seen the tests that lead to me trying to protecting my cells from getting above about 120 degrees and really trying to keep them below 140 degrees. Other stuff saying that under 2.5v generates a boatload of heat and should be avoided. Cold weather, found some stuff about how its fine for storage and they won't be affected long term in the Artic circle but nothing about cycle life when charging them at low temperatures. Anyone with a spare 40Ah prismatic cell that wants to send it my way(I'd pay you for it) and I could could it cycle it a few hundred times at -10f(-20c) but unfortunetly only at 7 amps charging. I can also charge either 10 amps or 55 amps but couldn't do it too many times because its not automated and I don't fancy babysitting a battery and its meter all day. I could discharge test it at up to 10C(won't work so well cold though) if someone wants those results.
 
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