Battery cooling

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Rory166
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Joined: Sat May 17, 2014 7:45 am
Location: Norwich, UK

Battery cooling

Postby Rory166 » Sun Jun 08, 2014 12:56 pm

Hi All

I have been giving some thought to battery cooling. I understand the Leaf uses air cooling as well as heating if temperature were too low. I may be mistaken but I seem to have noticed the battery getting hotter when driving economically at 40 mph than when driving at 70 mph which seems counterintuitive unless the forward motion of the vehicle contributes substantially to the air cooling. I think I have heard some vehicles use fluid coolant?

It seems to be common practice to stack rectangular lifepo cells close together on DIY packs, this is I suspect not a good idea. I have a pack of 200Ah Highpower cells which have seen substantial service and aprox half the cells seem to drop voltage on high load. My suspicion is that the cells in the middle of the block have been subject to overheating.

I have quantities of corrugated plastic separators which came from tall lead acid packs and were largely to allow swelling of the cells without the whole pack becoming jammed tight but clearly allowed some natural convection as well. I thought I might reuse these as a means of force cooling battery packs. Probably fitted with the corrugations horizontal and fans at the end forcing air along the corrugations, air passing along the largest sides for optimum cooling.

Rory
Electric Seicento conversion, Leaf

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skooler
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Joined: Fri Oct 19, 2012 5:19 pm
Location: Worcestershire
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Re: Battery cooling

Postby skooler » Sun Jun 08, 2014 4:56 pm

Rory166 wrote:Hi All

I have been giving some thought to battery cooling. I understand the Leaf uses air cooling as well as heating if temperature were too low. I may be mistaken but I seem to have noticed the battery getting hotter when driving economically at 40 mph than when driving at 70 mph which seems counterintuitive unless the forward motion of the vehicle contributes substantially to the air cooling. I think I have heard some vehicles use fluid coolant?

It seems to be common practice to stack rectangular lifepo cells close together on DIY packs, this is I suspect not a good idea. I have a pack of 200Ah Highpower cells which have seen substantial service and aprox half the cells seem to drop voltage on high load. My suspicion is that the cells in the middle of the block have been subject to overheating.

I have quantities of corrugated plastic separators which came from tall lead acid packs and were largely to allow swelling of the cells without the whole pack becoming jammed tight but clearly allowed some natural convection as well. I thought I might reuse these as a means of force cooling battery packs. Probably fitted with the corrugations horizontal and fans at the end forcing air along the corrugations, air passing along the largest sides for optimum cooling.

Rory


I wouldn't worry about cell temperatures unless you're into the 60s (centigrade). apparently LifePO4 is most efficient around 55c. heating in the cold is a much bigger issue.

what kind of currents are you putting through the cells and for how long?

suggest getting a laser thermometer such as the below and taking terminal temperatures after giving the cells a good frashing.

for reference, my 100AH sinopoly cells raise by a couple of degrees above ambient when pushed to 6c on a long drive.

http://www.ebay.co.uk/itm/Digital-Infra ... 3cd2f81505

Good luck,

Mike
Posts by Mike Schooling
Director and tech lead at indra.co.uk

Mazda RX8, Soliton Jr, 24KWH Sinopoly LiFePO4, Kostov 11alpha
http://www.diyelectriccar.com/forums/sh ... 61556.html


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