Air Circulation for Battery Box

[lettersize]

Guys, i am planning to use aluminium battery box for 8 100ah calbs cells.
The box will contain cells with installed MiniBMS cell modules.

In terms of safety, what kind of air circulation is needed?
Do this batteries become hot under usage? And is it required/recommended to have some kind of ventilation(several big holes)?
Or could i just place them in closed box and don't worry about it?

Attaching the picture of sample box, similar to which i am planning to use.

Thank you.

 

[dogman dan]

It should not get hot under normal usage. Warm yes, but not really hot. When the bms is really active, like top of charge when it's balancing dischargers get hot, it can use some space around it to let air circulate. So don't pack in insulation too tight around the bms.

In winter, you may find you have the opposite problem. A metal box can let wind chill really cool your battery, to the point where you lose a lot of range. So your real issue may turn out to be how to insulate it.

 

[Wheazel]

The batterybox setups ive built have all been pretty much babying the cells (18650 cells and lipo packs).
This way I can make more or less airtight boxes, and even have some insulation around the cells to "store" the litte heat they make. Which probably is close to none.
It does help versus cold weather and the battery gets cold slightly slower this way.

So what you need to know is how hard you will push the cells and what you can expect in terms of heat under those conditions.
Then make decisions about possible ventilation. The bms might need some ability to transfer heat, but it might be enough with an air volume around it.
An aluminum box is already a very forgiving box if heat tranfer from the box is needed.

 

[Ykick]

All wild guesses until we know by measurement or at least Amp draw how hot is hot? Or warm for the cells?

BMS w/balancing function will always require well thought-out air circulation. I don’t like majority of BMS balancers and often disable them (remove tiny bleed/load resistors).

Load current may also heat the BMS but IME as long as you double up the power rating of the BMS above worst case, that usually isn’t a problem.

Cells? Depends on specs, quality, condition, load. IR testing can eventually help someone better predict which cells are likely to heat more than others?

Myself, I’m never looking to cool my cells as they should never need it. If they do, something’s gone wrong. Times like the extreme cold most of us are looking to hold in whatever heat we can.

 

[lettersize]

guys, thank you for all the advices. Seems like i don't need to worry about it. Measured with clamp meter - it's 100amp continuous nous, and the 'rides' are pretty short. Will test for couple of days, but for know seems like couple of holes for ventilation will be enough.

By the way what non-conductive material I can use to put/cover insides of the box?
I was thinking smng like this.

 

[Wheazel]

Those probably works nice, I have used rubbermat, acrylic sheets and ground isolation foam among other stuff in the past.
The application sometimes requires certain properties, but most often anything nonconductive and stable will do the job.

 

[dogman dan]

That's coroplast sheet. But I never buy it. I just find it on the side of the road. Old political signs, or I never hesitate to outright steal signs that advertise some dumb ass work from home scam, or any sign posted illegally. Why not steal it, codes enforcement is going to remove the sign anyway?

This is great stuff to use for insulators, chafe protection, etc. You do have to make sure the sharp edges of the stuff is not rubbing a wire though. Lots of thick clear packing tape can soften edges.