The Stovebolt Site Forums The Shop Area The Electrical Bay generators

This is a little off topic because it's not really about GM. But on another forum I hear guys saying that the generators on some antique vehicles used permanent magnets instead of field coils. Nobody will actually say WHICH vehicles used magnets, though. Were there actually any such vehicles?

Good question, I've never heard of this though I can see if the vehicle is really antique than a simple DC motor run in reverse could have been used to provide a charge, just with no real voltage or current regulation.

Using regular permanent magnets (in the case of a regular DC motor run in reverse) would not be a very good solution because the voltage output would be directly proportional to the RPMs.... about the only control one could use on a setup like that is a cutout relay to break the connection, but this would only open if the "generator" was not putting out enough juice, and depending on the speed of the engine, the voltage could be very high!

Some early generators used a third brush to provide 'static' voltage regulation; that is, it would be manually adjusted to charge at an optimal RPM, but even in this circumstance the third brush still relied on a field coil to self regulate.

My thoughts would be that although this is theoretically possible, it is not practical and is most likely a wives tale or a story that got started when a farmer 'improvised' something to keep his tractor running! Otherwise, the vehicle would have to be pretty early to use something like that!

The purpose of polarizing a generator is to set the residual magnetism in the fields. The iron becomes a "permanent magnate". Magnetos are generators and use permanent magnets. An engine with a mag ignition needs no battery.