Capacitor Motors

Some single phase motors utilize a capacitor installed in series with one of the stator windings. A capacitor is an electrical device which can rapidly build up an electrical energy supply that can be used to create more current flow in the motor's windings. When input power is applied to the motor, the capacitor becomes charged up almost instantaneously.

The capacitor's energy helps create current flow in the start winding before the run winding gets any current flow. This difference in timing, called "phase differential", creates a rotating magnetic field in the stator. This stronger magnetic field induces more current into the rotor causing it to rotate quicker. The end result is a motor with the ability to start heavier loads requiring more starting torque.

This technique is widely used for motor applications like air conditioners and compressors. All the capacitor motors discussed in this section operate in essentially in the same manner.

The advantages that capacitor motors have over split phase motors are:

• They produce more starting torque, and
  
• They use less current while running at steady speeds

Capacitor motors vary in size ranging from small motors of fractional horsepower to motors up to 10 horsepower. Torque and voltage ratings of a motor determine the rating of the capacitor. The voltage rating of a capacitor must always meet or exceed the voltage requirements of the motor in which it is used.