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The permanent split capacitor motor
This motor has been the standard of the industry for many years. It is simple, efficient and low cost. It is a split phase motor, meaning it has 2 windings. One to give out of phase start torque and one that is the run winding. It has low to medium starting torque. It is often used in direct drive fan motors and refrigeration compressors that do not need hard starting torque. Unlike some other AC motors, the start winding is not disconnected when the motor has started. This makes the design somewhat different from some other split phase motors. The start winding is not as robust as other higher start torque motors. The reason for this is the capacitor limits current to the start winding.
The capacitor and the PSC motor
The capacitor used in the PSC motor is rated for continuous use. The design is different than the start capacitor. Below are 2 capacitors. On the left is a run capacitor used in PSC motors. It is usually but not always oval and encased in metal. On the right is a start capacitor. It is usually black and encased in a fiber housing. The start capacitor strength is much higher than the run capacitor, however it is used for starting only. For more on capacitors, go to this page.
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The PSC motor is a moderate starting torque motor. The capacitor provides the limited starting torque. The strength of the cap determines the torque. However, if the strength goes too high, the increased offset interferes with the starting torque. The video below tests starting torque using different capacitors.
The PSC motor will start and run without the capacitor. If power is connected directly to the start winding and the run winding, the motor will start and run but the start winding will overdraw current and burn out. Below the video explores how this works.
PSC motors are often times multi speed. This is so they can be adapted to different air flow requirements. The different speeds control the speed and amperage draw of the motor.
The run winding has several taps. Each of these taps are a different speed. The longest tap is the slowest speed because it has the most resistance. The shorter the tap, the higher the speed. The video below explains how this works and gives a diagram of the multi speed motor.
The run winding has several taps. Each of these taps are a different speed. The longest tap is the slowest speed because it has the most resistance. The shorter the tap, the higher the speed. The video below explains how this works and gives a diagram of the multi speed motor.