Capacitor Start AC Induction Motor
Modified split-phase motor with a capacitor in series with the start winding to provide a start “boost” is shown below. The capacitor start motor also has a centrifugal switch like the split-phase motor which disconnects the start winding and the capacitor when the motor reaches about 75% of the rated speed.
It creates more starting torque, typically 200% to 400% of the rated torque since the capacitor is in series with the start circuit. The starting current, usually 450% to 575% of the rated current, is much lower than the split-phase due to the larger wire in the start circuit.
The resistance start motor is the modified version of the capacitor start motor. The starting capacitor is replaced by a resistor in this motor type. The resistance start motor is used in applications where the starting torque requirement is less than that given by the capacitor start motor. Apart from the cost, this motor does not offer any major advantage over the capacitor start motor.
This device is used in a wide range of belt-drive applications like larger blowers and pumps, small conveyors, as well as many direct-drive or geared applications. [Schematic diagram source: Microchip Application Note]