Air Cooled Battery Case?

Technical discussion on converting internal combustion to electric
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OzSpider
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Air Cooled Battery Case?

Post by OzSpider »

Thinking out loud for my conversion https://forums.aeva.asn.au/viewtopic.php?f=33&t=7121 and looking for feedback from others lessons learnt...

With such a light car, I'm keen to keep it as simple as possible. For the battery cases, I've got 2 potential locations for the batteries, which also means a third option of a split battery case with half in one location and the other. One location is under the bonnet, the second is behind the rear seats on the floor. There is space in the boot, but I don't want to use that for batteries, more likely the charger or other bits to keep most of the weight inside the rear axle.

The battery will be about 28kWh of 42S2P NMC Prismatic. Rather than have a sealed battery case, I'm thinking about air cooling, probably not too sophisticated, but would like to add some lightweight finning to the prismatic cell casing, not exactly the image below, would need to be much shorter to fit between rows of cells, but you get the idea.
Capture.JPG
Capture.JPG (29.19 KiB) Viewed 224 times
Then, including in the design a filtered inlet/s, designed not to let water in and then some small fans on the battery case lid to draw air through. Has anyone tried anything similar? Was it effective at all?

I live in Qld so temperature in summer will be hard on the cells, and even passive airflow (not forced) through the pack could knock off a few degrees, compared to sealing up the battery case and having no real heat rejection.
antiscab
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Re: Air Cooled Battery Case?

Post by antiscab »

If you already have the cells, see how much they heat up from use.

Your issue may be stopping absorption of heat from ambient air, rather that the other way round
Matt
2017 Renault zoe - 25'000km
2007 vectrix - 156'000km
1998 prius - needs Batt
1999 Prius - needs batt
2000 prius - has 200 x headway 38120 cells
T1 Terry
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Re: Air Cooled Battery Case?

Post by T1 Terry »

Possibly using sheets of Lexan Thermoclear http://www.ampelite.com.au/lexan-thermoclear/ between the series cell prs to transfer heat away from the cells if air cooling is your preference, or a sealed battery box and flood it with E fuild and pump the vapour from the top of the battery box and pass it through a heat exchanger so it returns to a liquid and feed this back into the battery boxes. The same E fluid could be used as motor coolant and inverter coolant as well.

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OzSpider
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Re: Air Cooled Battery Case?

Post by OzSpider »

antiscab wrote: Tue, 23 Nov 2021, 18:48 Your issue may be stopping absorption of heat from ambient air, rather that the other way round
This is true during the heat of summer. A slide gate on the air inlets could be a simple solution to that, easy enough to include in the sheetmetal case. thanks
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Re: Air Cooled Battery Case?

Post by OzSpider »

T1 Terry wrote: Wed, 24 Nov 2021, 08:47 Possibly using sheets of Lexan Thermoclear http://www.ampelite.com.au/lexan-thermoclear/ between the series cell prs to transfer heat away from the cells...
thanks Terry, the section design is bang on near perfect for the gap between cells, pity the thermal conductivity of the polycarbonate is so low compared to metals. I'm thinking more like some very fine and dense finning, like an air conditioning condenser heat exchanger between the cells.
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Re: Air Cooled Battery Case?

Post by T1 Terry »

OzSpider wrote: Wed, 24 Nov 2021, 11:46
T1 Terry wrote: Wed, 24 Nov 2021, 08:47 Possibly using sheets of Lexan Thermoclear http://www.ampelite.com.au/lexan-thermoclear/ between the series cell prs to transfer heat away from the cells...
thanks Terry, the section design is bang on near perfect for the gap between cells, pity the thermal conductivity of the polycarbonate is so low compared to metals. I'm thinking more like some very fine and dense finning, like an air conditioning condenser heat exchanger between the cells.
What about something like this https://www.aliexpress.com/item/1005002 ... cfc604dfe1
it would hold a gap between the cells while allowing air flow that wouldcontact the cell faces as well as the aluminium mesh action as a heat transfer medium.

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Re: Air Cooled Battery Case?

Post by Bukes »

Some of the members builds go into a lot of detail about battery pack builds, including cooling. The Pajero is a good one.
If i recall, the hottest parts are the tabs that connect the battery to the bus bar, rather than the batteries themselves. Essentially every cell in the battery has a direct metal connection to the tab (duh ;)) so you can suck the heat out quickly if you cool those tabs.
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Re: Air Cooled Battery Case?

Post by Bukes »

Fastest EV in the world has air cooled batteries… just left an air gap between the batteries and ran air through it with fans:
https://youtu.be/cW2EJuP36vE
Good for close to 1Mw for 5 minutes at 355 miles an hour.
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Re: Air Cooled Battery Case?

Post by T1 Terry »

Over long discharge periods and high recharge sessions, the centre of each cell gets hotter than the rest of the case. With the Winston prismatic cells, the terminal seen from the top is just a lump of either copper or aluminium and the tabs from each relevant plate is attached with two x 4mm bolts and a bar each side to provide the clamping pressure. If the terminal gets hot, the plates inside the cell are mega hot, the only heat transfer path is a few micron thick copper or aluminium conductor sheet that the active coating is sprayed onto.

I've cut the top of quite a few cells that had suffered serious heating due to serious over voltage, and all of them, the copper sheet plate as well as the aluminium sheet plate, had oxidised severely due to the heat and simply broken away from the terminal itself.

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