Tom's Life Bits

A capacitor start motor is a split-phase induction motor with a starting capacitor inserted in series with the startup winding, creating an LC circuit which is capable of a much greater phase shift (and so, a much greater starting torque). The capacitor naturally adds expense to such motors.

Another variation is the permanent-split capacitor (PSC) motor (also known as a capacitor start and run motor).[4] This motor operates similarly to the capacitor-start motor described above, but there is no centrifugal starting switch,[4] and what correspond to the the start windings (second windings) are permanently connected to the power source (through a capacitor), along with the run windings.[4] PSC motors are frequently used in air handlers, blowers, and fans (including ceiling fans) and other cases where a variable speed is desired.

A capacitor ranging from 3 to 25 microfarads is connected in series with the “start” windings and remains in the circuit during the run cycle.[4] The “start” windings and run windings are identical in this motor,[4] and reverse motion can be achieved by reversing the wiring of the 2 windings,[4] with the capacitor connected to the other windings as “start” windings. By changing taps on the running winding but keeping the load constant, the motor can be made to run at different speeds. Also, provided all 6 winding connections are available separately, a 3 phase motor can be converted to a capacitor start and run motor by commoning two of the windings and connecting the third via a capacitor to act as a start winding.