Car alternators...

isnt a car alternator just an electric motor that is acting as a generator? is there anyway to put two old matching ones on a base, attach tires, and power them with a car battery?

crispyjones8 years ago
An alternator produces alternating current (AC) that is rectified by diodes (the diode trio) to produce DC voltage for the vehicle charging system. So, unfortunately, you can not apply DC (like from a car battery) to it and use it as a motor.
pbates1236 years ago
I know this is an old post I just thought a more through response would be helpful for future reference.

You have mixed two things into one question. Older vehicles used Generators. They are essentially DC motors and they can be used as a motor. In-fact they make pretty good motors at that. DC motors that are spun by the shaft will produce electricity proportional to the speed of rotation. In fact a very common "generator" used in wind generators is a 90 volt DC motor often used in tread mills and the like.

Alternators which typically have multiple coils that are energized sequentially produce three outputs or phases. Each phase is then rectified by diodes and added together. This output becomes DC.

Using an alternator as a stepper would not be very practical as an alternator only has three poles. Most steppers have many more poles. The granularity of the step (how many degrees the shaft moves each step) depends on the number of poles in the stepper.
I've heard that alternators can be operated as stepper motors, by applying appropriate waveforms to the different phases of the windings.  However, this is more useful for robotics or "numerical control" applications where you need to move motors by increments.

A starter motor or fan motor is a better choice, depending on how big a thing you want to move.