Oil cooling for 18650

[DrKraut]

Hello,
my idea is to use the air gap between the cellls if you weld them using these cell holders. The complete battery pack comes in a enclosed box, eg aluminium, with 4 connectors. 2 electrical and 2 fot the oil input and output. Transformer oil would be a good choice since it is used it hv applications with great succes. Only downside is the increased weight from the added oil.
My plan is to use Samsung 25R cells.
What do you think?

 

[e-beach]

Makes me wonder why your cells are getting hot enough to need cooling. But if you stack them one atop the other, you might have 6mm or so for a small copper tube to pass in between sets of cells.

Letting air flow through the batteries works as well, unless the ambient air temperature is very hot, and you wouldn't have to worry about fluid leaking in your battery pack.

 

[DrKraut]

They don't get too hot but i think cool batteries will last longer.
Does anybody know if the 18650 are 'oil proof' or is it a risk to flood them in oil.

 

[jonescg]

I'd like to see some experiments done with oil baths too. I'm interested to see if say, transformer oil would be OK with LiPo pouches too. Cause I can't think of any other potting compounds which are great conductors of heat, but not electricity. And without adding significant weight...

 

[knighty]

no experience with transformer oil

but I think you want to use the thinnest oil you can find

specific heat capacity of different kinds/grades of oils are close enough that they won't make much difference,



but a lot cleaner/tidier/less mess/easier might be to put thin sheets of steel between the cells, with a right angle on the end to but up against the battery box/case


i think you'll only really need to worry about heat build up in the centre of the pack, where the cells heat each other / can't cool

 

[dogman dan]

Match your discharge rate to the cells ability, and your batts won't overheat. But in a hot climate, there is still the problem of cooling them while parked.

I solve that with bikes by bringing the battery inside in summer, but I'd be screwed if I bought a leaf. I'd have to air condition the garage.

 

[bzhwindtalker]

Interested in this too, I think i will try it with a sample pack and bath a 160 cell panasonic PF if succesfull.

 

[redilast]

I would guess that the short bursts of increase temperature due to discharging a battery at moderate discharge rates is less concerning than high storage temperatures above 25C.

My electric car has chilled liquid cooling, and it even kicks on in the summer while the car is in the garage, to keep the batteries cool. Oil cooling will never cool the batteries more than ambient temperatures. And on a hot day in the sun, a battery could easily hit 40-50C when parked.

 

[Overclocker]

sounds like a lot of complexity for little gain

it would make more sense for larger packs where heat get trapped in the inner cells. for typical ebike packs where no cell is more than 2 cells deep it's a lot easier to just bond them to an aluminum outer shell w/ thermally-conductive adhesive, which is what i did here:

 

[bzhwindtalker]

On the contrary I think this can be super simple if you already have the right alu box for your pack. Just fill it with the proper fluid and voila

 

[Overclocker]

On the contrary I think this can be super simple if you already have the right alu box for your pack. Just fill it with the proper fluid and voila

wait you're not gonna use a radiator? just circulate oil inside an aluminum box?

 

[bzhwindtalker]

Yes, the surface of the box can already dissipate quite good and is in direct contact with the rest of the alu frame, similar at what is done on the alta MX bike with the frame acting at heat sink.

 

[jonescg]

Good candidate for some phase change material like parafin...

 

[Overclocker]

Yes, the surface of the box can already dissipate quite good and is in direct contact with the rest of the alu frame, similar at what is done on the alta MX bike with the frame acting at heat sink.

oh ok in that case it would be simple. but that cell arrangement doesn't allow much coolant flow over the cell walls

you might also want to strip the cells naked for maximum effect

 

[999zip999]

An aluminum box with aluminum rods from the outter heat sink skin and to the inner hot parts of the pack. Aluminum is a great heat conductor. Or aluminium tubes with thru air holes one side to the other. Lots of contact area. Plus fan. No leaks.

 

[999zip999]

Where do cells heat up first from the pos end or the neg end or from the center ?

 

[madin88]

I would guess that the short bursts of increase temperature due to discharging a battery at moderate discharge rates is less concerning than high storage temperatures above 25C.

My electric car has chilled liquid cooling, and it even kicks on in the summer while the car is in the garage, to keep the batteries cool. Oil cooling will never cool the batteries more than ambient temperatures. And on a hot day in the sun, a battery could easily hit 40-50C when parked.

exactly!
battery cooling was invented to keep the cells cool in hot climate if the EV is parked in the direct sun.
The heating from discharge is almost insignificant IMO, and if a battery become hot during discharge, it anyway isn't properly designed and cooling will not help much for lifespan..

If one plans to abuse a battery, he should rather heat it up before the ride (for lower internal resistance), instead of cooling it :lol:
just google: "lipo heat box"

 

[Hillhater]

That may be correct for some applications, but not all.
Tesla,s cooling system is sometimes used to pull heat out of the pack during supercharging.
Formula E car traction packs are liquid immersed for direct cooling, as are some of the hybrid storage packs on F1 cars

 

[macribs]

I would guess that the short bursts of increase temperature due to discharging a battery at moderate discharge rates is less concerning than high storage temperatures above 25C.

My electric car has chilled liquid cooling, and it even kicks on in the summer while the car is in the garage, to keep the batteries cool. Oil cooling will never cool the batteries more than ambient temperatures. And on a hot day in the sun, a battery could easily hit 40-50C when parked.

Well the simple way would be to add a pump and a radiator with a small fan. Monitor the oil temp and if oil temp reaches pre set value then the pump and fan kicks in and cools it all down. Pump and fan could even be run by a separate pack to avoid stealing ride time from pack.

For those who ride year around, embedded in the cooling loop the could be a valve closing the circulation from radiator and a heater inside reservoir to keep batteries nice and cuddly warm even in freezing temperatures. Heater got a temp sensor hook up to it, and only runs in certain temperatures. Again it all could be run from stand alone pack to avoid stealing ride time.

 

[macribs]

On the contrary I think this can be super simple if you already have the right alu box for your pack. Just fill it with the proper fluid and voila

Yeah added thermal mass and direct fluid connection between batteries and alubox/frame makes the entire bike a heat sink.

 

[spinningmagnets]

I am certain a non-conductive oil-bath will work, even without circulation. However, I would weigh that against a cell configuration that allows some flow through the pack, and add a server centrifugal 48V air-fan (or two 24V fans in series?).

They are cheap and come with ball bearings. An air-fan wouldn't use as many watts as you might imagine, and off course, the weight would be much less than the oil-bath...That being said, I am curious to see your results.