A123 20Ah Pouch Cell Packaging and Cooling

[Sutho]

Hi All,

Along with many of you, I have ordered some samples of the low cost A123 20Ah Pouch cells which I should receive next week. My project is a car, so all being as it should, I will be taking a large risk and ordering a much higher quantity.

I have read a lot of about these cells, particularly on this forum (thanks doctorbass) and seen the videos of Jack Rickard's cell packaging techniques....but I have also done a lot of searching on A123s (and others) module packaging techniques and designs. In these designs there is a lot of emphasis on the cooling of the pouch cells which I think many people are discounting.

The A123 prismatic module has heat sink plates between all cells. These apparently have a paste to ensure good heat transfer, and the whole unit is designed to be fixed to a cold plate system. Chevy Volt and Fisker Karma animations show heat sink plates between all of their pouch cells and water flowing through the whole pack. I read somewhere that the objective is to not allow the pack to rise above 60 deg C.

I have plans to package my cells in 8s3p blocks which will then be connected series to achieve the required voltage. I am concerned about failure or extremely shortened life due to unacceptable cell temperature rise and have been trying to devise some suitable cooling methods.

I don't think placing the cells against each other without some method of extracting heat will result in a reliable battery system......and although they want their systems to be safe in all climates, I really don't think A123 and the larger car manufacturers would go to so much trouble in the cooling areas of their battery pack design if it wasn't necessary. A lot of patents have been registered in this area of EV battery design.

Comments or suggestions please?

Regards,
Sutho

 

[nechaus]

I have also ordered these cells.
I think I will try a pack with no cooling, but just running the cells under 5 c

if needed to cool them, I would prob just use thin aluminium sheeting with micronized silver.
but im really really hoping they will be good to go @ 5 c with no cooling

 

[Sutho]

I have also ordered these cells.
I think I will try a pack with no cooling, but just running the cells under 5 c

if needed to cool them, I would prob just use thin aluminium sheeting with micronized silver.
but im really really hoping they will be good to go @ 5 c with no cooling

I'm pretty confident that mine will run at 5C max as well. I have been thinking along similar lines....but it's no menial task to package and connect these cells.....particularly since I'll have almost 400 cells. I don't really want to do it twice or have to purchase replacement cells because heat killed the originals. It's probably enough risk buying cells such as these in the first place. :wink:

 

[peterperkins]

I run 50 cells in a block with no active cooling.

Max current is around 5C. I live in a temperate climate in northern UK.

Highest temp I have seen after a really hot day with an exhausted pack soc <10% is 50C. Normally they run near ambient temp and warm to ambient + 10-20C higher as the drain.

The only cooling I need to add is a fan to extract the heat from the battery compartment on my vehicle as it has no real ventilation.

Note in my experience (Cells in use in the car for nearly two years) the cells start to heat quite a bit more when soc is <35% or so.

When i finally do my insight conversion I will be using around 300 cells and will not be using heat plates etc just fan cooling of the battery compartment.

I charge at 5A and that never causes an issue.

 

[nieles]

i think it is more important to heat the pack in the winter (when the temperature is below 0 deg C), than cooling the pack in the summer.

when the cells are at a higher temperature, the internal resistance of the packs is lower. which means less voltage sag.
ofcourse exceeding the max temperature of the cells is also bad, so there the sweet spot IMO would be 10-20 degrees below max temperature

 

[tef]

What do you think about casting them in polyurethane like jack richard did?

I thought a long time about methods for packaging and connecting them together.
So far, casting is the best (most stable) solution for me.

I have ordered 60 cells for my scooter and will connect them in 30s2p.
I think that I'll only add togehter two cells at a time with a casting thickness of about 2mm and separate the finished plastic blocks with aluminium sheet.
So I hope that the temperature will not get too high. During winter the aluminium sheets could get removed.
If my calculations are correct, it will cost me about 150USD of resin for 60 cells.

The only thing I worry about is expansion of the cells.

 

[Sutho]

Jack's polyurethane casting was inspiring.....but I would be concerned that it would trap the heat and would not provide enough compression on the cells.

I'm thinking maybe some slightly extended aluminium plates between each cell and air/fan cooling when necessary to extract the heat. This would allow the cells to be suitably compressed and still have a relatively simple method to get the heat away.