Vacuuform Battery Cover

battery_holder_cardboard_toolAfter building a PVC pipe battery holder for my electric bike, I used a vacuum form machine to make a polystyrene battery cover. I built up a cheap tool form using cardboard (which turned out to be too week, but it was quick).

Vacuum form complete

Vacuum form complete

As the vacuum was forming the polystyrene around the cardboard the box started to deform so I had to release the vacuum before the styrene had fully formed itself to the PVC pipes, but it got close enough to be screw mounted. Continue reading

Electric Bicycle power circuit

Bolting a DC motor to the front basket of a bike and running a chain to the front wheel takes care of the mechanical linkage needed to make an electric powered bicycle, but you also need to provide power to the motor, and control that power in some way.
Luckily, the same place that sold me the 250 watt motor also sold a 40 amp speed controler. (It cost $33, or more than any single other part of my e-bike project.)
40A motor controller

The speed controler is controlled by most standard e-bike throttles, such as this one from Currie Technologies. I also attached two 12v 5AH batteries in series to provide 24 volts. Because I calculated that my 250 watt motor running at 24 volts would draw approximately 10 amps, (250/24 = 10.4), I added a 15 amp fuse to the circuit. (The first 15A fuse was replaced by a second 15 amp fuse after it saved my speed controler from damage when I accidentally reversed the polarity on the power…)
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Adding an electric motor to a bicycle

250 watt motor with sprocket and chain

I purchased a surplus 250 watt motor with a matching wheel hub and 90 tooth sprocket. The motor has an 11 tooth sprocket, and both the motor’s sprocket and the hub’s 90 tooth sprocket are designed for #25 motor chain, which is slightly smaller than standard bicycle chain.

To get the hub and 90 tooth sprocket on the wheel, I had to remove the existing hub and rebuild the wheel on the new hub. Luckily the two hubs were close enough in size that I could re-use the existing spokes. Following the instructions on Sheldon Brown’s website, and also refering to this website I was able to re-spoke the wheel.
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Currie Technologies 6 pin Diaganostic throttle pin-out

I purchased a surplus Currie Technologies “Diagnostic” throttle. (Which includes 3 LED’s labeled as 1/3, 2/3 and full charge indicators) It has a six pin (7 cable) connector with no pin-out diagram.

Currie Technologies diagnostic throttle

Currie Technologies diagnostic throttle

After opening it up, it appears that the blue, black, and red wires are connected to the throttle sensor itself, while the other four wires (White, Gray, Yellow, Green) connect to the LED circuit board.

The pin-out ordering is as follows, from the bottom of my picture up:

  1. Red/White (Throttle/LED, sharing a pin, + voltage)
  2. Black (to throttle, I assume Ground)
  3. Blue (from throttle, I assume signal)
  4. Green (Full LED)
  5. Yellow (2/3 full LED)
  6. Gray (1/3 full LED)

I connected the Red/Black/Blue wires to a motor speed controller that had a 3 wire throttle connection (matching them up to the Red/Black/Green wires from the controller) and it worked great!

The LED pin-out is as follows:
White (positive / Vcc)
Gray – 1/3 empty LED
Yellow – 2/3 full LED
Green – Full LED

Note that I was able to get the LED’s to light up with a 3V source, but I believe their forward voltage is less than 3V and you should use a current limited supply so that you do not burn the LED’s out.

Electric Scooter Power Usage Details

I purchased a used Navajo Turbo Z 24volt electric scooter. The person I bought it from had installed two brand new 12V 7.0Ah batteries, similar to the battery in this data sheet. Note that because the scooter will discharge the batteries in less than an hour, the pack’s usable capacity is closer to 4Ah. Because the batteries are sealed lead-acid, they are heavy, approximately 6lbs each, and the pair make up approximately 35% of the scooter’s 34lb total weight. (Most of the rest of the weight comes from the hefty all-steel frame, and the 5lb 200-watt motor.)
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