The workings of a Single Phase Electric Motor


Single Phase Motors are generally used in applications of low power rating. They work off a Domestic 230-240V supply commonly found in your typical household as well as some Industrial units. This blog post will give a brief overview of how a single phase motor works.


A Single phase motor is made up on a number of components, the main components are the rotor, which is the rotating part, and a stator which assist with the rotation of the rotor. There are also two copper windings in the motor, one is the main winding and the other, which is placed perpendicular, is the auxiliary winding. Depending on the type of Single Phase motor, there are also components such as Capacitors and a Centrifugal switch allowing the switching between capacitors.


There is a number single phase motors available, however in this article we will stick with the most commonly used Permanent Capacitor or the Capacitor Start/Capacitor Run Type. In a Capacitor Start/Capacitor Run type single phase motor there are two windings, a start and run winding, the start circuit has two capacitors and a centrifugal switch. The start capacitor gives the motor an increased starting torque of approx. 170-230%. When the motor nears its running speed the centrifugal switch cuts the start capacitor out and the start winding remains in circuit with the run capacitor giving the motor more power. Due to the high starting torque this type of single phase motor is good for applications such as car lifts, compressors, conveyors and crushers. In a Permanent Capacitor type single phase motor a capacitor is connected permanently in turn eliminating the need for a centrifugal switch as used in a capacitor start/capacitor run type of motor. This style of motor is used for low starting torque applications such as Fans, Blowers and Pumps where the starting torque requirement of 50-70% is sufficient.


Single Phase Motors only runs off one phase, due to an Alternating Current (AC) source, the motor can only produce an oscillation magnetic field that pulls in one direction and then the other and not a rotating type field which in turn simply causes a twitching of the rotor. However, if the rotor begins to rotate it will continue due to this continuous oscillation of the magnetic field. The important feature of a single phase motor is how to start the rotation. The single phase motor has been continuously developed over the years to find a suitable solution to how to get the motor to rotate from standstill, which include, producing a second phase to help produce a rotation magnetic field to using capacitors to shift the magnetic field on start up.

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