Lesser Lithiums Lose Power When Colder

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xyster
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Last seen: 12 years 4 months ago
Joined: Thursday, November 16, 2006 - 20:11
Points: 137
Lesser Lithiums Lose Power When Colder

Just a li-ion performance consideration I've run into using cheap 18650 lithiums that other folks have noted with Thundersky cells too. My batteries are spec'd for 1.5C, but only provide 1C at less than 50F.

http://tech.groups.yahoo.com/group/ThunderSky/message/868
The internal resistance of the 2003 Thunder Sky TS-LP8581A 100 AH
cells in my electric motorcycle was always high enough to cause
embarrassingly slow hill-climbing in cold weather unless I kept them
near full charge in winter. It gradually increased by about 50% to
become VERY embarrassing in cold weather. I noticed that on Thunder
Sky's web site the maximum current rating of the equivalent TS-
LCP100AHA cells is now much higher. I phoned Dennis Doerffel of
REAPSystems to ask for his views about this, and he said that there
was indeed a great improvement. He also said he had some new cells in
stock. I have now bought a new set from him. They are a vast
improvement even on what the previous cells could do when they were
new. They will easily give over 100A at half charge and a temperature
of about 2 deg.C. The old ones would give no more than 15A under
these conditions, even when they were new, although they would give
over 100A on a warm summer day. The internal resistance of the old
cells varied by a factor of about 3 between the best and worst, and
it also increased considerably over the first minute or so after a
load was applied. The new cells are all almost identical and also
their resistance does not increase with time after a load is applied.
I think Thunder Sky have abolished the only real drawback that
their batteries had.

pm
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Last seen: 12 years 1 day ago
Joined: Sunday, November 19, 2006 - 15:21
Points: 2
Mine seem fine

I've been riding a bit more lately - now that my body is getting used to being cold all the time. I've ridden 3-4 times in the last week. The temperature outside was between -1C and 4C (approx. 30F to 40F) on the rides. I had no problem at all pulling 21-22A out of my 12s8p pack (current cut-off is supposedly 20A and was 20A all summer, but nowadays I'm edging on 22A frequently... I think it's the cold). I monitored the pack using my Hyperion E-meter.

The pack is well packaged (to prevent damage) and this results in it being fairly well insulated - which I thought was a concern in the summer, but could be a bonus now that it's winter. I have a temperature probe buried in the heart of the pack - pretty much dead center in the middle. I've been storing the pack in the garage now which is now between -2C and 6C (approx. 30F to 45F) so it's not particularly warm (insulation on the pack or not) when I use it.

The manufacturer's datasheets - which all-battery.com seems to have removed - didn't show anywhere near the temperature degradation you are seeing. They showed - if I remember correctly - about a 10% reduction at 0C, although the performance falls off dramatically from there. I can't find the datasheets to refresh my memory, but I am certain that they do not show a substantial reduction in capactity/performance at 0C. The steep slope of the curve is below -10C... if I remember correctly.

Xyster, we are using the same cells. I have no idea why I'd see different results that you are, but I am definitely seeing the cells deliver over 1.8C at ~0C. The pack is wired with 12AWG stranded copper, and each set of 4 cells is double-tapped (the wires run in a circular loop around the 8 cells and then I wire on both ends to the next cell). I don't think that it's my wiring that's the difference though. Have you checked the internal resistance of all of the sub-packs? Perhaps one of the sub-packs has a bad cell or two.

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