Description: These motors are used where very low power is needed or where a three phase power system is not available. They are available with a cast iron or aluminum frame. They use a capacitor for start-up and operation. The motor’s variable speed is controlled by voltage (as opposed to frequency in three phase motors), using simple thyristor-based variators which are electronic controllers that alter the duty factor of the voltage; control is made via a simple potentiometer, like the volume of a stereo.