Battery box that doesn't trap heat

Overclocker

Overclocker

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battbox.png

we've all seen the typical ebike battery pack. some are even encased in (insulating) foam. heat gets trapped inside. a typical hailong pack doesn't have any effective heat path to the outside air.

on the other extreme there's Tesla's liquid cooling. not really viable for ebike packs.

so here are two SEALED battery boxes. both with aluminum side covers. the objective is to transfer as much heat from the cells to the side plates.

the LEFT box simply circulates the inside air. flows air between the cells which are slightly separated.

the RIGHT box uses soft TIMs (thermal interface material) which have horrendous bulk thermal conductivity :lol:

the left box is going to work better, right?
 
btw those are existing battery boxes. if i were to build from scratch w/ heat dissipation in mind i would bond the cells directly to the aluminum outer shell w/ thermally-conductive adhesive

2vsrtzr.jpg
 
Yep, potting is the best solution. Most electrically insulating thermal potting epoxies are pretty ordinary though - best I've seen is 2.0 W/m.K
 
Unless you are severely abusing the cells, the potting approach will work fine. There is so much surface area you don't need super high thermal conductivity. I have a pack that uses silicone glue as the heat transfer compound and a plastic box and it seems to work quite well but I'm only running about 3C discharge max.

The fan will work too and probably be better at keeping the temperature of the cells uniform, but fans are a pain and can fail.
 
Air transfer means moisture can get in.

Heavy gauge aluminum case and fully potted with a good thermally conductive compound would be best.

But as stated, unlikely the expense of such optimization is actually required or will pay off financially in actual longevity increases.
 
If heat trap is a problem, its not your problem. Your problem is you are beating the pack to shit. Your discharge rate is too high, if its getting all hot.

Trapping in warm is fine, especially in winter. But in a hot climate, your battery will be 110f anyway. If its getting hotter than that, then lower the discharge rate. But no worries if the pack only gets to temps where you can easily touch it. Like 150f max. But it will be better to lower the discharge rate if it does get a lot above ambient temps in Phoenix AZ.
 
dogman dan said:
If heat trap is a problem, its not your problem. Your problem is you are beating the pack to shit. Your discharge rate is too high, if its getting all hot.

Trapping in warm is fine, especially in winter. But in a hot climate, your battery will be 110f anyway. If its getting hotter than that, then lower the discharge rate. But no worries if the pack only gets to temps where you can easily touch it. Like 150f max. But it will be better to lower the discharge rate if it does get a lot above ambient temps in Phoenix AZ.
Click to expand...


that's like saying Tesla is beating their packs to shit that's why they're watercooling them with afaik chilled water :lol:

it's just a matter of sound engineering to provide a heat path for warm/hot components. just think of it this way, with proper cooling you could beat your cells harder. that's exactly what tesla is doing :thumb:
 
If the pack is thermally insulated, like stuffed in a padded bag with no air flow, then there is no place for the heat to go and the pack temperature will rise even under normal loads.

Circulating air inside a sealed container works well if the outside of the container has cooling. I prefer the no moving parts solutions for simplicity.

If the cells have a solid thermal path to the outside (no air spaces) it will be a big improvement over the insulated bag.
 
Overclocker said:
that's like saying Tesla is beating their packs to shit that's why they're watercooling them with afaik chilled water :lol:
Click to expand...

But that's true right? Tesla is beating the batteries like a slave... Lol
200kw... Damn.. human can get fried by touching it.
I think someone test it can reach 320v x 1000A on a tesla motor
images


Edited:
From the tesla forum, the battery should be at 375v and to get the motor run at 200kw it needs 500A at least
If the car have 8000 bateries. Means the configuration is somewhat like 100s80p
And 500 divided by 80p... Each cell need 6.25A (around 2C continuous)
This one going to be require special cooling.
But something doesn't add up, if it run on 2C continuosly means the battery will only last for half hour before reaching the end of the capacity...hmmm

For a DIY ebike normaly i target under 1C to keep the temperature acceptable :)
 
well the model S supposedly were using NCR-BE which are like GA cells w/a bit lower capacity i.e. not 30Q/25R levels of internal resistance (i've personally tested the BE and GA cells to get hot at just 7A w/o cooling). then tesla came up w/ an elaborate watercooling system to push these cells very hard during both charge and discharge
 
kuririkura said:
But something doesn't add up, if it run on 2C continuosly means the battery will only last for half hour before reaching the end of the capacity...hmmm
Click to expand...
It would be really hard to keep the motor at 200kW for half an hour. After a few seconds you are practically airborne. The average will be much lower than the max.
 
Yep. one of the beautiful things about electric drivetrains.

A battery that can handle a few seconds at high power is substantially smaller than one that can do it continuously. Same goes for motors.

I think electrics have a very bright future in motorsports because of this.
 
Tesla's cooling system is primarily to ensure they last a long time. The cell cannot put out any more power than it's intrinsic properties will allow.
 
jonescg said:
Tesla's cooling system is primarily to ensure they last a long time. The cell cannot put out any more power than it's intrinsic properties will allow.
Click to expand...


GA is a 10A rated cell which isn't going to last a very long time at those currents inside a hailong case. in other words cells are already thermally limited at their rated currents if you have longevity in mind
 
Yeah for sure. The GA just doesn't strike me as being a particularly good cell for e-bikes. Unless they are limited to under 350 W at all times.
 
Rather than the heroic efforts required to actively cool cells

budget being constrained

seems to me being "more realistic" about performance is what's required.

Yes there is a limit to the energy density Ah capacity we want to carry around

but increasing that's the easiest way to keep the C-rate down, buy not only range but longevity and **prevent** overheating.

Or as above, reduce our power output expectations.

Just because that newer expensive battery chemistry **can** give us a higher C-rate doesn't mean we **should** take advantage of it to push right up into its self-destructive range.

The biggest benefit may be running cooler at the same output level.
 
I think an active temperature control for the cells also gives them predictability in terms of cycle performance, which is pretty important to their business model.

By knowing that the cells have always operated within specific thermal and power limits, they can predict with some accuracy how long they can be expected to last, and how their performance will decrease over that lifetime.

We don't have that kind of control over operating conditions with our ebike packs, and as a result we either get reduced life or reduced performance from the same cells.
 
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