Do It Yourself - Home Built Electric Bike

Don Chandler, 2006

Goals

My goal was to build my own electric bike as inexpensively as possible to learn about the technology.

Design and Build

Start with an old bicycle. Choose one with the now standard 5 rear forks to fit the new hub motor, wheel size the same as the hub motor wheel, and brakes and cables to match.
Buy an electric bike hub motor kit. This should include the motor, controller, brake handles and optionally the throttle. There are over a hundred manufactures in China. Finding one locally may be hard, Choose a motor between 200 Watts and 500 Watts, either 24 volts or 36 volts. This is the costly part. ($150-$500).
Buy some batteries: 20 Amp hours should give about 10 Km range ($60). More is better but heavier and costlier. Find a way to mount the batteries on the bike. It is important to mount them as low as possible and midway between the wheels to maintain good weight distribution and dynamics. This is the biggest challenge. If possible, mount them so they can be easily removed for charging.
Mount the hub motor wheel, controller, throttle potentiometer and brake levers on the bike. Wire it all together, adding a fuse and power switch. Insulate all the connections from water and fingers. Dress the wires neatly. Miscellaneous parts, wire, connectors, etc. ($100)
Buy or build a battery charger suitable for the battery type and voltage of choice. ($75)

Test

Go for a ride. See how far you can go on a battery charge. Try climbing hills and compare the range to riding on the flat. Be careful not to completely drain the batteries as it shortens their life a lot. Let your friends try it out and share your experience. Try commuting by e- bike instead of by car. No sweat!

What I Learned

I made a lot of mistakes. The first was to use a really old bike. The rear forks were too narrow and had to be stretched to fit the new motor. The slot had to be filed to fit the axle.
I chose a cheap imported motor and controller. I burned up the controller and had to replace many of the electronic components and re-solder the whole board.
I mounted the batteries in a great location for weight distribution and dynamics, but they can't be removed easily for charging inside, so I have to bring the charger to the bike.
I mounted the controller under the seat width wise. It gets in the way of leg movement.
I used a bike with 27 rims. I had to get new brakes and cables and mount them on the new 26 rim.
I wired it without providing a connection for a charger. I have to unplug the batteries to charge them.
I tried using a car charger. These are 12 Volts so I can only charge one battery at a time, a real pain. It would be good to have the charger mounted on the bike with the batteries and be removable.
I chose a less expensive motor of 200 Watts. 500 Watts would be better on hills.
I chose lead batteries. Lithium is worth the cost for weight and range.
Hub motors are good and are the norm. A few bikes have the motor mounted on the crank so they use the gears of the bike. This is the best design for power and efficiency. Even driving the chain would allow the use of the rear gears.
Converting a bike is basically the same theoretically and electrically as converting a car. It is an inexpensive project that can be done over a few weeks or months with useful results. I recommend it as a good electrical project for high school students or hobbyists. See www.veva.bc.ca