Temperature rise in powerwalls and cell packs

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ozz93666

Member
Joined
Feb 22, 2017
Messages
341
I recently watched this 3 min video by Damian ...http://ashtangapictureproject.com/wp-content/uploads/2014/10/dwipadasirsasana159.jpg

He's building a 20s10p pack for a road vehicle and at first sight it seems quite wrong ... he's hot glueing the cells in a very tight pack , and shrink wrapping them so it's very difficult for the heat to get out ...

I forgot an important point ...he uses new cells which will have a low internal resistance and so will produce less internal heat when charged or discharged ( I don't think the type ofcells he uses ,NCA ,have a particularly low int resistance compared to laptop)

Damian tells us he's never had more than a 15C rise in temp in the center of his pack at 1C discharge .

I did an experiment to see what would happen with (almost) perfectly thermally insulated recycled laptopcells at 1C discharge .. after 10mins the temp had risen 21C ... so we do need to space salvaged cells to get the heat out . I would guess the black holders generally used, allow enough cooling even at high discarge...

Is it all about how new the cells are that determines the amount of this internal heat?

Tesla road vehicles use new cells , but still have the cells spaced far apart ...and use a liquid cooling system ... is that really necessary?

I would bet in most conditions it's not... the thing is tesla cars have to be able to handle all extremes , temperatures in Saudi Arabia can get upto 50C , and someone therewill quick charge , and then go for a drive ... and the comfort zone for cells is only up to 60C.
 

Elmo

Member
Joined
Feb 19, 2017
Messages
189
1C is too much for laptop cells, they are really engineered for about a two hour power drain so .5C. I test at 1A and most cells only get a little warm. If you are draining your powerwall in an hour you are doing something wrong.

I tested some INR18650 25R cells yesterday and even they got a bit warm at 1A, almost as much so as some laptop cells I've tested.

My understanding is that the Tesla will back off the power for battery heat reasons after an (unspecified) number of hard launches.

When I started testing laptop cells for ebike use some years ago I was overly harsh and my expectations of what you can get out of these cells was too high, they are fine for a long range cruiser that takes some hours to drain the pack but nearly useless for high performance.
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,659
As Elmo said. In real life 0.5C is more than enough. Ie 1A as i have been saying to many times and i almost feel like a bitch :D Dont take me wrong though because you can drain more but i dont recommend it.


Tesla has a quite advanced system and they are constantly monitoring the temperature on the packs.

I dont personally recomend for ebike that is high powered. For a 250w bike and if you got a larger pack thats totally fine though :)
 
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