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Discussion Starter #1 (Edited)
I did some searching and didn't find anything on this...

General rule of thumb for lead battery EVs that I've seen are that you loose half your range in the cold of winter (no pack heating). I realize there are many factors that effect range beyond pack chemistry, but I'm just trying to get a ballpark estimate for sizing a pack and I'd like some idea of how lithium will be effected by cold. Is this rule still the same for a lithium pack?
 

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Thanks DIYguy. I don't know how I missed that on their sheets before. Thats exactly what I was looking for.

In Wisconsin cold is around 10F/-12C. It definitely gets colder, but not too often. If I used the -25C line I'd definitely be fine

Looks like you only loose ~8% capacity. Thats a lot better than I had thought!

 

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Daox, Expect to lose a little bit more than that as you are pulling a heavier load. I also would plan to keep the SOC above about the 20% point or otherwise that is when the voltage will likely drop heavier with load.

Keep in mind that the colder it gets, the less amperage you can pull from the cells so you need to plan for that. I just asked /Per(pm_dawn) from Sweden in another thread that says that 2C is the max draw on their ThunderSky pack but I'm not sure if that is at the -28 degrees C(-20f) or not. Hopefully we will get a response, I just asked about an hours ago. This is the thread
http://www.diyelectriccar.com/forums/showthread.php?p=216852 Possibly Per can give us an idea for range loss. It might not be a bad idea to ask the same question in that thread in case the question isn't seen in this thread.
 

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Yea PM didn't specify that she "couldn't" draw more than 2C. I took that to mean she just never goes over 2C. If the pack is sized right and according to how you drive you may never go over 2C, regardless of conditions.

But what I do know is if my pack gets cold, it acts like its' about dead! I built the battery boxes with that in mind. I used old political signs that look like cardboard to insulate the sides and bottom on each box.

In the summer the top is open but when it gets cold I cover them with bubble wrap. That does keep them warm even when it's 20F outside as long as I don't park it for a long while in those temps. It keeps them around 40-45F while I'm at work.
 

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Attached is a sheet from headway for cold weather performance of their 38120S 10AH cells (x axis plot is a bit weird, it's AH without a decimal, 955 on the far right is 9.55 AH) At first I asked why the C rate was so low for the test and their reply was discharging much faster would heat the cells internally and throw off the results. They said even 0.5C started to heat the cells and change the results.
 

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.. At first I asked why the C rate was so low for the test and their reply was discharging much faster would heat the cells internally and throw off the results....

Yeah - cold weather performance is kind of a red herring... the internal resistance shoots up dramatically when cold, but that causes the cells to heat up rapidly, thereby lowering the internal resistance.

So, drive gently for the first minute or two to warm up the cells and then you should be fine... very little actual capacity loss, in other words.

Controllers with a minimum pack voltage function (most programmable ones these days) can automatically do this for you because the higher internal resistance when cold means the cell voltage will sag a lot more, so the pack will reach LVC at a lower current.

Of course, you have to actually SET the minimum pack voltage to something reasonable first. ;)
 
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