There are three types of AC motors that are used to drive fans – 3-phase motors, permanent split capacitor (PSC) motors and shaded pole motors. The type of motor required for a given application is dictated by the input voltage available in the application and the amount of power required to drive the fan.
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PSC and shaded pole motors are used for single phase AC input.
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Shaded pole motors are suited for low power fans.
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A more powerful single phase fan requires a PSC motor.
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Shaded pole motors are more cost effective but are limited by their lower power.
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PSC motors require an external capacitor for proper operation.
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A 3-phase AC motor is needed when the application has 3-phase AC input.
When the application requires DC input, a brushless DC motor is typically used. A brushless DC motor uses an electronic circuit and permanent magnets to generate rotation. The end result is a highly efficient and highly reliable motor. The commutation electronics are typically built right into the motor so the user only needs to apply DC voltage to the motor. Since brushless DC motors require electronics to function, they are often referred to as Electronically Commutated or EC motors. Because EC motors have electronics, speed control and speed monitoring functions can be done very easily.
The last type of motor to discuss is the line-fed EC motor. These motors are also brushless DC motors but are used with AC voltage. The AC input coming into the motor is rectified to a high voltage DC. These motors are used where typical PSC, shaded pole or three-phase AC motors have historically been used. The benefit of the line fed EC motor is the higher efficiency, controllability and long life that a brushless DC motor offers. All power conversion and drive electronics are located within the motor.
