Build a bike battery container

October 31, 2007 9:33 PM

I'm working on an electric recumbent bicycle using a Bike-E as the bike part. I want to hang my batteries below the seat by building two containers to hang on the sides of the Bike-E's alloy beam body. What's the best way to build the container?

The batteries are a pair of 10 lb. rectangle shapes, 3"x5" by 7" long. I've got some sheet metal, a zip tool cutter, and a brazing torch. If I build open topped boxes for the batteries, I can hang one on each side of the alloy beam body, puts bolts through the body connecting the containers and put the batteries inside. The bike side of the container would be taller to facilitate putting it on the bike.
While that might be effective, manufacturing a container this way will be a lot of sparks flying and hot metal while using the zip tool to cut the metal. I'm thinking there must be easier ways to build shapes and forms. Using carbon fiber seems like a lot of toxic waste to work with. I'm coming up against this problem often as I contemplate bike projects I want to do that need some unique shape or form to do.

posted by diode to technology (7 comments total)

Why do you need boxes? Why not hinged metal straps or metal strip baskets? Lighter, less cutting and welding.
posted by weapons-grade pandemonium at 9:45 PM on October 31, 2007

Why do the containers need to be rigid? Use leather.
posted by flabdablet at 10:26 PM on October 31, 2007

20 lbs is a LOT of weight -- you want the batteries well secured to minimize rattling and swaying (which could affect balance).

Fillet brazing is the way to go. It is the most durable and versatile construction method that is within reach of the skill-level and finances of an amateur like yourself.

Stick with your plan. Leather straps? You gotta be kidding.
posted by randomstriker at 12:07 AM on November 1, 2007

I've mounted the batteries in various ways previously, for example lashing them to a mesh bike basket on the tail. For various reasons it would be best to have them mounted by themselves on their own supports.
I had thought initially to make a simple L shape the length of the batteries, a shelf they could sit on and then lash them to the bracket. The box shape is a way to contain them and prevent them sliding forward or backwards.
They might be lighter than 20 lbs, like 16 or so. It's still a compact inertial mass that needs to be secure. This isn't an unusual project. There's a fair amount of people retrofitting bikes for electric power.
I have an oxy-acetylene torch and brazing rod, so looks like I'm good to go. I was hoping to avoid having to cut metal using my zip tool as it's eats up the cutting disks like candy but looks like that's the only real alternative for me.
posted by diode at 5:15 AM on November 1, 2007

If you do this kind of thing frequently maybe you should look into getting on old, used shear and press brake and learn how to use them. It would make forming sheet metal much easier.
posted by neat-o at 7:00 AM on November 1, 2007

A pair of tin snips can be had for only a few dollars (three piece set for US$10), probably cheaper than the zip tool disks.

Brazing is expensive, both for rod and for gas. There are amazing adhesives available now available from autobody suppliers used for installing patch panels. They'll be cheaper and you'll get a better result unless you have a lot of practise brazing flat sheet metal. Accounting for the expansion/contraction from the heat makes it quite a bit different than say brazing bikes together. Or you can buy a gasless MIG rig for less than a $100.

If it was me though I'd vacuum form a set of boxes out of some ABS or Lexan. They won't corrode and are abrasion resistant. Also lighter than metal boxes. All you need is a plug (a wood block a bit larger than your batteries), a vacuum frame and box (easily made out of whatever scrap wood you might have hanging around), an oven (the one in your kitchen will work fine) and a household or shop vac.

If you do decide to braze the boxes together make sure you are using satin finish sheet metal and not galvanized.
posted by Mitheral at 12:18 AM on November 2, 2007

Vacuum forming....eureka!
posted by diode at 9:35 AM on November 5, 2007