July, 2022:

Heinkel Cars
Heinkel Kabine before conversion

If Ernst Heinkel had the option of electric drive when he designed the Kabine would he have chosen it? After having thought about it for a long time I decided to make my own Heinkel an EV to find out. Here’s the story of my conversion and you can decide for yourself!

If you’ve never owned a Kabine (or Trojan as they are called in the UK) you probably picture them as cute, head-turning, fun little vehicles. While those things are all true, once you own one you learn their dark secrets- they’re slow, smell like exhaust, and are very loud inside. With an EV conversion I hoped to make driving the car as fun as it looked.

While I knew a lot about Heinkels I knew little about EV’s, so I expected bumps and surprises along the way. I set some lofty goals to measure my success:  

  1. I wanted the converted car to appear indistinguishable from a traditional Heinkel.
  2. The conversion should be reversible with no bodywork alterations in case someone wanted to restore it to be “original” again.
  3. I wanted a range of 40 miles (70km) at an average speed of 40mph, with the ability to go 55mph (90km/m) for a brief period.
  4. I wanted modern acceleration.
  5. I wanted to end up with a car that did not smell like exhaust, vibrate, or be so loud I couldn’t talk to the passengers.

Designing and building the EV:

The first lesson I learned is that you can’t have a successful EV without having a place to put the batteries. I wanted them behind the firewall for safety purposes. After I determined the types of cells to use (24 LiFePo4 cells in a series configuration) it took several attempts to fit them into the car. Here’s what the battery pack looked like before I installed it in the car:  

Custom built 72v battery pack for Heinkel Kabine
Interconnected cells in a waterproof case with battery management system: Heinkel EV Conversion LiFePo4 battery pack

Once I had a solution for the range, I needed a motor that could reach the desired speed. I used a QS-Motor 8000-watt hub motor to drive a 12” wheel. Because the wheel uses a low-profile tire, the height and circumference of the drive wheel almost exactly matches the original Heinkel setup. Here’s a picture:

Heinkel EV Tires are nearly identical in height
Heinkel EV Conversion New and Original Tire Comparison: New wheel is .25”(6mm) taller (unladen) than the original 10” wheel with Trelleborg tire

8000 Watts is the equivalent of 10.72 HP, all of which is available immediately when you apply the throttle. This compares to 9.5HP of the original car at 5600 RPM.

Mounting the hub motor under the car required extensive design and mockup. I prototyped four different versions in wood and steel before I got the clearances and suspension geometry correct. The swingarm looks like this:

Heinkel Kabine EV Swingarm
Heinkel Kabine EV Swingarm (3rd revision)

I attached the swingarm and battery pack to the original engine mount via a ¼” (6.35mm) aluminum plate. This enabled a “plug and play” configuration that makes installation much simpler and easier than the original 200cc engine.

Heinkel EV swingarm and battery pack mounted
Heinkel EV swingarm and battery pack mounted

Here are “before and after” photos of the engine compartment (before photo is from the Heinkel Club of Germany website)

Heinkel Drivetrain comparisons
Comparison of original 200cc motor to EV drivetrain

Once I solved those design issues, I needed to find space for the electrical components and wires. A 72-volt system like I’m running requires robust (and larger) components. I used a petrol tank filler neck for the charging port, and used the gas tank mounting area to house the onboard charger and motor controller:

Heinkel EV Charging Setup
Mounting the electronics. Fake filler cap houses the charging outlet

I still had other components to mount, so I built an extra box against the inside of the firewall to house them:

Heinkel EV Control Box
Box behind seat holds additional components and battery disconnect switch

I’ve been a woodworker for decades and purchased a hobbyist CNC from Sienci Labs to make most of the parts that I didn’t weld. That included my new shifter and my digital dashboard.

Heinkel EV Shifter
New shifting plate with integrated dual USB charging port and EV on/off switch
Heinkel EV Digital Dash with 3D printed steering wheel insert
Heinkel EV Digital Dash with 3D printed steering wheel insert

I converted the mechanical gas pedal to an electric throttle. I used the original long carburetor cable that I connected to an electronic motorcycle twist throttle. This was another idea I borrowed from Marcelo Spina, who converted a Heinkel EV in Argentina. He was a tremendous help in all aspects of my EV build, and I can’t thank him enough. Here’s a photo of an early mockup:

Heinkel EV Throttle with cable attached from the rear
Heinkel EV Throttle with cable attached from the rear

Road Testing:

Just like a regular Heinkel, the work didn’t stop when the build was complete. I’m still road tuning the car. With an EV the process is much cleaner- instead of using wrenchs I use a Bluetooth tablet connected onboard software apps to change the operating parameters of the battery and controller. If something doesn’t work to my liking I can pull over to the curb, make a software change, then try again. There are the usual mechanical things to look at, and the car is so quiet now I hear things that were previously masked by the engine noise.

Would Ernst Heinkel have made an EV?

While I’m not 100% done I can say with certainty that converting to EV makes the Kabine a much more enjoyable car. Let’s see how I did with my goals:

Looks like an original Heinkel?Yes
Is it reversible?Yes- I only drilled 5 6mm holes
Can I drive 40 miles?It looks like I can, but I haven’t tried yet
Will it go 40-55 mph?Yes
Modern acceleration?Yes! It is very quick
Exhaust smells gone?Yes
Vibrations gone?Yes
Is it quiet?Yes- it’s too quiet! I may have to add some sort of sound to let other cars and pedestrians know I’m there

 I think Ernst Heinkel would be proud of an EV Kabine.

The license plate is the only hint that it’s an EV!
The license plate is the only hint that it’s an EV!