As the name suggests, permanent-split capacitor motors (PSC motors) have a run-type capacitor which is left permanently in series with the starting winding during operation. This is to say that they do not have a starting switch or a capacitor which is used only
for starting. Thus, the starting winding becomes an auxiliary winding when the motor is up to running speed.
The design of PSC motors means that they cannot provide the same initial boost as motors with separate capacitors. Their starting torques are quite low, between 30 to 90% of rated load, so they cannot be used for applications which are hard to start. This is offset by their low starting currents - usually less than 200%
of rated load current - which makes them the perfect choice for applications with high cycle rates.
Permanent-split capacitor motors offer many benefits. Their running performance and speed can be tailored to meet specific needs, and they can be designed for optimum efficiency and high power factor at rated load. As they need no starting mechanism, they can be reversed easily. Finally, they are the most reliable
single-phase motors available. These advantages are the reason why Grundfos uses PSC single-phase motors as standard for all applications up to 2.2 kw 2-pole and 1.5 kW 4-pole.
Permanent-split capacitor motors can be used for many different applications, depending on their design. Low-inertia loads such as fans and pumps would be a common example.
The PSC motor. Schematic diagram and torque/speed curve
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