Adding a skin to the battery box frame

February 28, 2010 · 4 comments

Iโ€™m finishing the battery box for the chopped mountain bike project. This is one of the last major projects I need to finish before I can put this bike back into service.

If you want to see which electric bike this battery box is going on, you can view the first test ride video by clicking on this link.

This project started with several drawings and measurements. The next step was to fabricate the frame. The video of the battery box frame fabrication can be seen by clicking on this link.

I designed it to fit my SLA batteries. I tried to make it large enough to fit 12ah LiFePO4 batteries once the SLAs wear out.

Now Iโ€™m putting a cover on the frame with aluminum sheets. Iโ€™m making a video of this fabrication which will be posted soon.

The drawing on the left is going to be the top. It has several bends, notches and angles. I’m going to need a press break which I’ll use to bend the sides.

You can read about all the posts on this project by clicking on this link.

{ 4 comments… read them below or add one }

1 Brian Jackson March 1, 2010 at 10:59 am

So you’re welding the battery box frame in steel and skinning it in aluminum? Looks good ๐Ÿ™‚

I would however suggest trying to do the whole thing in aluminum – obviously because it’s lighter. Also obvious is the reality that very few people can weld aluminum. I therefore recommend this brake from harbor freight.

It’s cheap and it works great for making cheap and light-weight aluminum doo dads ๐Ÿ™‚


2 Dan March 1, 2010 at 4:47 pm

Hi Brian,
Funny thing; I was just looking at one of those brakes. I’ll order one tonight so I can finish the lid.

For this design I wanted to over design it because of the weight of the SLA batteries. I wanted it very stiff and strong. I plan to cut holes in it to lighten it up later when I switch to LiFePO4. For now it’s a functional prototype to see how it works and how it can be improved for the next design.

If I wanted to replicate it using aluminum, could I use angle stock and bolt it together? If I could weld aluminum, I think using thicker plates and no frame would be ideal.

Someday I’ll be welding aluminum. For now, I’m alright with the extra weight. ๐Ÿ™‚


3 David Herron (vIsForVoltage) March 24, 2010 at 5:02 pm

Just came across your site a few days ago and see this. I’ve been looking into housing a lithium pack (see battery pack tetris) and hadn’t considered making a metal box like this. I’d been thinking instead of plastic boxes – there are some really tough plastics. But..

For this what I would do is construct it with stainless steel angle pieces (the kind with predrilled holes) and just bolt them together. Should work fine.

I’m wondering why you used metal for the ‘skin’? My thought after looking at this would be to use thin wood pieces as the skin. I’m fearing the metal might short a battery or some such, whereas wood is nonconductive. Especially if you’re in an accident …

4 Dan March 25, 2010 at 6:58 pm

Hi David,
Plastic looks like the way to go the way you are going to carry your tetris bats. Looks good.

Angle stock should work nicely. I’ll try this for my next box and use aluminum angle for weight reduction.

The main reason I used steel and welded was because I had the material already and wanted to over design it because of the weight of the SLAs. Itโ€™s a very solid box and wonโ€™t flex much if at all.

I thought about using wood for the skin but I like the looks of aluminum. Aluminum should weather better too.

I put a lot of insulation on the terminals and padding such that the box would have to take quite a blow to cause a short. If the box was hit hard enough to cause a short, I would have more to worry about than the batteries shorting. ๐Ÿ™‚

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