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The tedious jobs of dismantling and restoration are done, so we can engage ourselves in the more productive “conversion”.

Basically, this means to bolt in the electric motor where the engine used to be, and to eventually snap in the accelerator's wire rope.

Finally, it is important to remove any disturbing reminiscence to the “combustion” past of the car.

Now the conversion is complete, and we can call it a day and have a beer.

— end of chapter “conversion”? —

No, not yet!

what are the challenges?

In reality, a few more things have to be considered before the car is roadworthy. This means that this chapter “conversion” does not end here and even has quite a number of subchapters.

traction battery

Trivially, the electric motor requires a battery instead of the fuel tank. Due to its inevitably lower energy density, the battery is bulky and heavy and its proper and safe accommodation poses quite a challenge. See sections “auxiliary_frame” and “battery_boxes”.

electrical isolation

Since the electric drive runs at higher voltage (in this case around 100V), the traction “grid” has to be separated - and even electrically isolated - from the original 12V grid of the car. Exchanging energy and information between the two grids becomes the next challenge. Therefore, the part “wiring” (including some electronic gadgets) has become quite voluminous.

substitute for all engine "features"

Furthermore, many of the assemblies within a conventional car have “grown up” together with the combustion engine, and now need an appropriate substitute:

brake booster

It requires vacuum as a power source. Vacuum is also required for other, exotic purposes such as (with this particular car model) switching the ventilation between “fresh air” and “circulated air”. Gasoline engines provide vacuum at their air intake. For EV conversion, an electrical vacuum pump is required.

power steering

The steering gear is hydraulically powered via a pump that is attached to the engine. The pump requires that the engine spins continuously while the car is in operation, e.g. for reversing into a parking lot. In case of electrical drive, we want to allow the motor to stop when it is not required for propulsion, so it will normally not be suited anymore for driving the hydraulic pump. Besides, you need a more-expensive two-ended motor to drive the pump via a belt transmission. And finally, the hydraulic power steering costs a lot of precious energy. For my project, I have decided to simply replace the power steering by a conventional steering gear. This has already been mentioned in the chapter “base vehicle - restoration - front axle”, see also some pictures of the steering gears there.

air condition

It is also powered via a compressor, and same concerns apply to it as to power steering above. Except that the power demand of an A/C compressor is huge, about 3..5kW. Technically the best, but sadly also a very expensive solution is to install an electrical compressor that can be fed directly from the traction battery. I will leave that open for better times to come …


As a thermal engine, a combustion engine naturally produces a lot of heat, and ample of it is available via the coolant liquid. In an electric car, the heat either has to be produced electrically (though it is actually a waste to use low entropy energy for heating), or via combustive fuels. When using the latter, the car is of course not “zero emission” any more. In addition, the Austrian regulation demands a time-consuming and costly approval process for a plastic fuel tank. So I decided to make an electrical heater. See chapter “heater”.

In addition to above assemblies that depend on the combustion engine, there are two further aspects that directly affect operation and handling of the car:

parking lock

With conventional shifted cars, you usually put in a gear when parking, so that you dont have to rely on the parking brake alone to hold the car on its place. The electric motor will not build up a significant torque when the controller is off, it will just readily spin when driven via the gearbox (note that during operation, you can well do regenerative braking). This seems to be a certain safety issue, and one will have to take other measures for securing the car when parked.

sound indicates state of operation

The sound from a running engine provides a clear information both to the occupants of the car itself and to the outside traffic participants, that the car has been taken into operation and everyone better rush for a safe place. A silent electric car may just start going without a warning. To avoid that the driver himself makes a dangerous mistake e.g. by pressing the accelerator in the believe that the ignition is off, the European Regulation r-100 demands a visible indicator for the “ready” state of operation. together with an audible warning signal when the driver's door is opened while the car is in this state.

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astra_conv/conversion/conversion.txt · Last modified: 2014/03/16 11:20 by richard