What should I do to an electric motor, that is always connected to a battery, to convert it into a generator?
Answer:
Add a diode in series between the motor and battery. The cathode (-) of the diode is connected to teh positive of the battery. This will prevent the battery from supplying current into the motor. Spining the motor fast enough in the proper direction will allow current to flow into the battery.
The down side to the use of a diode is that you will have a voltage drop of 0.7 volts across the diode. The diode will also have to be sized large enough to handle the current flow from the generator.
Depends on the kind of motor. If it is a DC motor, it can be converted into a DC generator by providing a controllable power source to energize the field windings (unless the field is permanent magnets). It will be of limited usefulness, as pulling a lot of power out of a commutator is problematic.
Obviously, your motor is a DC type. A dc motor is also a Dynamo that will produce DC current if a mechanical rotation is applied to it. If your Intention is to charge the battery, You have to do a little modification to prevent the current from the battery flowing back to the motor. You can use a diode or use a regulator for a better circuit.
You need a regulator, this contains diodes but also has other circuitry to prevent overcharging.
I recommend using an alternator for applications of this kind, they have all the right circuits in them and are cheap from the junk yard.
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