What are you building your battery boxes out of?

[EVconverter]

Hi Gang,

I've been going back and forth about what to build my battery boxes out of.

I want to use my car as something of an education vehicle, so I'm considering doing the boxes out of clear polycarbonate. I don't have any experience with it. Is there any downside other than not being as strong as a metal box? What thickness would it have to be to be strong enough to hold a ~350lb battery pack in a 14"x15"x24" space? I'd be bolting it onto the car's frame with an aluminum cradle of some sort.

Maybe I'd be better off doing an aluminum box with a polycarbonate top so people can see into it?

Any suggestions would be appreciated, especially if you have direct experience working with polycarbonate.

If anyone knows a company that makes closed battery boxes, I'd also like to look into that. I've spent way too many hours designing the battery packs and I'd buy an off the shelf solution if such a thing exists.

[arber333]

Hi Gang,

I've been going back and forth about what to build my battery boxes out of.

I want to use my car as something of an education vehicle, so I'm considering doing the boxes out of clear polycarbonate. I don't have any experience with it. Is there any downside other than not being as strong as a metal box? What thickness would it have to be to be strong enough to hold a ~350lb battery pack in a 14"x15"x24" space? I'd be bolting it onto the car's frame with an aluminum cradle of some sort.

Maybe I'd be better off doing an aluminum box with a polycarbonate top so people can see into it?

Any suggestions would be appreciated, especially if you have direct experience working with polycarbonate.

If anyone knows a company that makes closed battery boxes, I'd also like to look into that. I've spent way too many hours designing the battery packs and I'd buy an off the shelf solution if such a thing exists.

Hm... polycarbonate? You would best be glueing sides to a ridge. Use epoxi and glass fiber for reinforcement.
Upsides are; nonconductive, good thermal isolation, good impact properties, could be made to custom dimensions...
Downsides; difficult to work with, requires additional substructure to be bolted on the chasis, you really need alu fittings

Aluminum box made from alu sheet 3mm.
Upsides; Alu can be bought anywhere, Good mechanical properties - stiffness, easy to work with, to drill etc...
Downsides; Conductive Must find AC alu welder, bolted or riveted alu is about the same difficulty as poly box
https://leafdriveblog.wordpress.com/tag/battery-box/

1mm Inox box
Upsides; all of the above, can be readily welded with variety of welders
Downsides; all of the above, difficult to drill large holes...
https://mazdamx3ev.wordpress.com/2024/0 ... ttery-box/

[espriev]

How about a cage made from solid square aluminum bar, either welded or drilled, tapped, and fastened together to support the weight of the batteries and bits to be attached to it, then poly top, bottom & sides that are attached to this frame with threaded fasteners?
The battery-box to frame mounts can attach this way as well. Poly sheets can be cut to size by your local supplier, cutting is the hard part.
It is easy to drill.
It is good to use a rubber washer & fender washer on both sides of the sheet, for mount bolts a nylon bushing helps to prevent cracks and a metal spacer inside of that can make it so the clamping force is on the spacer, not the poly.

[jrbe]

Aluminum can be mig welded. It's a bit tough to weld because of it's high thermal conductivity, pulls the heat out of the weld area. Preheating can help,

Aluminum can also be bonded but requires surface prep to remove the oxide layer. These adhesives usually require a minimum and maximum thickness between layers to be effective and some require baking which can both really complicate things. Quite often mechanical fasteners are used to aid in overall strength and hold pieces while it cures.
PEM nuts or clip nuts in bent sheet metal is my preferred route. Bolt on lid, glued seams for the box, siliconed lid. In cold weather this will likely continuously suck the heat out of the batteries.

I personally wouldn't want plastic as the main containment for crash safety. It's strong until it shatters. Something non conductive inside the metal box / between batteries is good / required for isolation.