generator.?

Question

How do you convert a DC motor in to a generator? And how much current will it produce. I was gonna use a 12 volt motor from a tire inflator.

Answer 1

If the motor is a permanent magnet motor (like the one in the tire inflator probably is), then all you have to do is spin the motor and you'll get DC out of the 'generator'.

Spin it in one direction and you'll get DC "plus" and "minus" from the 2 leads. Spin it in the other direction and the "plus" and "minus" will be reversed. Spin it at the rated RPM (when 12 volts is applied as a motor) and you'll get 12 Volts out. Spin is faster and the voltage will go up -- spin it slower and the voltage will be less than 12 V.

Note: The above only applies to permanent magnet motors and other self-excited DC motors. It doesn't apply to externally excited DC motors.

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Answer 2

It is likely that whether the motor has permanent magnets or has a series connected field winding, it will generate just by turning the shaft. If it doesn't have permanent magnets, it will probably have enough residual magnetism to get it to start generating and provide its own field.

It should produce 12 volts if turned at its normal operating speed. It can probably safely produce the same current that is requires to operate as a motor. If you connect a load that takes more current, it is likely to overheat and eventually fail.