What is function of run capacitor?

Answer 1

Start and run capacitors are normally used in AC motors to aid in starting and running efficiency. Both capacitors are wired in series with the start winding of the motor. The reason they are not both called start capacitors is that the start capacitor gives the motor more torque to overcome the fact that it is at standstill, and then automatically disconnects itself from the circuit. The run capacitor gives the motor better running efficiency and remains part of the circuit, it is therefore called the run capacitor. Three phase motors are able to start more effectively due to the nature of three phase power. These capacitors will likely be found in single phase AC motors. This is because a single phase AC source rises and falls from zero, in a three phase source the second phase sine wave starts going upward before the first phase wave has a chance to fall completely to zero. Thus a three phase motor spends more time per cycle at its rated voltage than the single phase motor, and has an easier time starting instantaneously.

Answer 2

In a single phase induction motor, it is necessary to create a shifted second phase to send into a separate start winding. This creates a rotating magnetic field which reacts with the rotor's embedded shorted copper bars to drag the rotor along with the rotating field. the device which causes this phase shift is a start capacitor placed in serieswith the start winding. Once the rotor achieves a certain minimum velocity, a centrifugal switch will cause the start winding to drop out of the circuit and no more current flows into it or the start capacitor. In some induction motors, the phase-shifted circuit is always kept online, and in some designs there are two phase shifted windings, one of which is active only during startup with its own starting capacitor, and one of which is always active. The capacitor in an always-active phase-shifted induction motor winding is known as a run capacitor.

Answer 3

A capacitor-start motor is one in which the capacitor is in the circuit only during the starting period: the capacitor and its auxiliary "start" winding are disconnected automatically by a centrifugal switch or other device when the motor reaches a predetermined speed.

A capacitor start-and-run motor is one in which the capacitor remains in-circuit during both start-up and running periods of operation.

Answer 4

A run capacitor is made for continuous and heavy workloads. It helps enable the running of two motors at the same time. Items that use run capacitors are AC units and heat pumps.