AC Motor Capacitors for Self-Starting AC Motors

An AC motor is an electric motor that runs on alternating current supply and has two main parts. The stationary part is called the stator and the rotating part is called the rotor. It has a starter winding with an AC motor capacitor which allows the single-phase motor to self-start.

ac motor

There are many ways in which an induction motor can be made self-starting. Two common methods are the Capacitor Start Induction Run Motors and the Split Phase motors.

When a capacitor is introduced in an AC circuit, the current leads the voltage by a phase angle. The AC motor capacitor which is used in these AC motors is a visible electrolytic one attached outside the motor.

A motor capacitor serves the purpose of changing the current to the windings of the motor to generate the rotating magnetic field. Some uses of motor capacitors are seen in hot tubs and heat furnaces. The three main kinds of motor capacitors are the following:

Run capacitors: These capacitors remain connected to the auxiliary coil even when the start capacitor is disconnected. They are great for continuous use and are active whenever the motor is running.

Start capacitors: These are used during the start-up phase of the motor and once the rotor reaches an ideal speed, they are disconnected. This speed is normally around 75% of the motor’s maximum speed. The capacitance values of start capacitors is over 70 µF and they have different voltage ratings, depending on their application.

Dual run capacitors: As the name implies, the dual run capacitor acts as a support to two electric motors. Examples of such capacitors are heat pumps and large air conditioners. It saves space by combining two physical capacitors into one case.