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Using VW Generators as Motors

This page is about using a VW generator as a motor for a light-weight electric vehicle. They should make a nice motor for something like a go-kart or electric bike. They can handle 30 amps continuous and run fine on 24V and can probably handle up to 48V (I haven't tried this yet, but I will).
Before we get started, you'll need to know how to find the right kind of generator. The 12V generators came on Type I, II and III VW motors from 1966 until 1973. Before 1966 VW used 6V generators and from 1973 on (and on all type IV) they used alternators. The alternators won't work for us, the 6V generators should work fine(I haven't verified this though)
Many other makes of cars used 12V generators and they all should work as well, however I can't guarantee the following instructions will work.

Motors and generators are basically the same thing, if you turn a motor faster than it wants to turn it will generate electricity. If you apply voltage properly and don't force it to turn, it will turn on it's own (motor).
When used as a motor these generators function as a "Shunt" motor, this means we can control the speed of the motor by adjusting the voltage through the field. The hard part for some people to understand, is that as you reduce the voltage in the field, the motor will speed up. And if you increase the voltage in the field, the motor will slow down.
This can be used to slow the vehicle down. If we increase the voltage in the field the motor wants to run slower, remember if we force a motor to spin faster than it wants to it generates electricity. So we end up taking energy from the foward motion of the vehicle and converting it to electricity and store it in the battery, this is called regenerative braking.

Anyway, the big advantage of shunt motors is that the field only has a maximum of 8 amps flowing through it. Compare this to the armature that can have 100 amps or more, and it's easy to see that controlling the field is simpler and cheaper than controlling the armature.

Basically there are two windings inside the generator: A stator or field winding and a rotor or armature winding. The field winding is divided into two coils and attached on opposite sides of the motor body (it replaces the magnets you would find in a permanent magnet motor). The armature winding is wrapped around the armature (the part that spins).
The generator has three electrical connections: D+, DF, and the body of the generator (there should be a screw to connect a ground wire to).
Some use screw terminals and some (newer model perhaps?) use spade connectors:

The field coil is wired from D+ to DF. The Armature coil is wired from D+ to the body (use the ground screw).

How to wire it up.

You'll need a 12V battery and some way to adjust the voltage in the field. The simplest way is to use something like a 50 ohm reostat, it should be rated for at least 100Watts. However if you don't spend much time going slow (full field voltage) then you can get away with 25-50Watt.
Wire positive terminal on the battery to a switch and from the switch to D+. Wire the negative terminal to the body(use the grounding wire screw). Finally connect your reostat from DF to the negative battery terminal.
Be prepared for some really UNimpressive torque, you can easily stall the motor by just grabing it with your fingers.

To make this motor really shine, you need to run it on 24V or higher. Here you can see that I've tapped the pack at the 12V point to run the field. This works great! The motor has plenty of torque and spins about twice as fast.
Note the second switch to turn off the field, this is because if you just disconnect D+ there is still a path for current from DF to D+ to the body (grounded) and back to the battery. Use a double-pole switch to turn off both at once.
Caution:Don't run the field on anything higher than 12V. I haven't tried it, but I think the field windings will burn out if you do. The resistance of the field is only about 1.5 ohms, at 24V that would be 384 watts of heat being generated! Besides that, if you are wasting 384 watts, your efficiency will be lousy.

While a reostat is simple, it also wastes power. A better way is to use a PWM controller, I'm working on one that uses about $10 in parts. As soon as I verify that it works I'll include the details here.
Also with a PWM controller we don't have to tap the pack at 12V. We can run it at 24V and just never go beyond 50% duty cycle. (or 36V and 33%, etc.)

For those of us who live in the USA, you might run into a problem getting a sprocket that fits. As are all things VW, the shaft is metric (13mm I believe). However you can get a sprocket with a 1/2" bore and drill it out to the right size.

One last note: if you plan on running these things for more than a few minutes at high power, you'll probably need to include a cooling fan. In their normal environment these are cooled by the fan on the VW engine.
Adding a fan should be easy, there is a large hole in the side of the generator designed for just this purpose. Best way would be a simple duct between a 12V fan and the hole. However; you can probably just mount the fan next to the hole.
Another option, if you are using a type I or II generator with dual shafts, is to mount a fan blade on the unused shaft and duct it back through the motor. The type III generators only have one shaft so this won't work for them.

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