EV Conversion Speedometer Project

Now we’re in unchartered territory. The original Heinkel speedometer looked like this:

Remember that Heinkels were economy cars, the speedometer only recorded the bare minimum- speed and miles traveled, But if you paid extra you could get a real (or a fake) clock! The speedometer measured travel by a cable from the top on the swingarm of the internal combustion engine. Since I no longer had an internal combustion engine I needed to find another way.

Here’s my solution; a Chinese-made E-bike speedometer:

To make the speedometer function I ran an additional set of three wires back to the controller. The speed reading comes from a tap into one of the phase wires coming off of the motor. The battery status comes from wires attached to the positive and negative connections to the motor controller.

Getting the bike speedometer to fit took some doing. First I built an enclosure to close the gap between the original opening and the speedometer LCD screen. I chose quartersawn white oak because I had a piece and it’s completely too luxurious for this application.

Because I wanted to keep the 12 volt system completely separated from the 72 volt drive system for safety purposes, I used two small LED lights to act as the turn signals and high beam indicators. I got the idea from seeing photos of a Heinkel Trojan speedometer:

Finally I had to create a bezel and mounting bracket to hold them all together. I made those on my CNC.

After assembly I road tested and calibrated the speed against a GPS speedometer app I had on my phone. Adjustments were made by turning a tiny screw on the circuit board in the unit.

Here’s the completed speedometer:

And a video of the lights and turn signals: