MAKE pal Dino Segovis brings us this handy tutorial on running a stepper motor in “reverse,” i.e. turning the shaft mechanically in order to generate electrical power, instead of the normal usage. He writes:
Any electric motor will also output a voltage when it’s freely spinning. Stepper motors are much better at this because they have many times more poles to pass next to each other thus generating electrical pulses.
The AC current can be used as-is, he reports, to run LEDs, or easily rectified to give DC. [Thanks, Dino!]