Understanding AC Gear Motor Design

Sinotech    December 21, 2012

120 Watt 90mm AC Gearmotors

120 Watt 90mm AC Gearmotors

AC gear motors are electric motors that use an alternating current. They generally have two parts: the outside stationary stator and the inside rotor. Slip rings or a permanent magnet generate the magnetic field on the rotor. The stator has coils that receive an alternating current, which produces a magnetic field that rotates. An output shaft that’s attached the inside rotor of the AC gear motor acquires torque via the rotating field. The two most common types of AC gear motorsare synchronous and asynchronous motors.

AC Synchronous Motors

In synchronous motors, the rotation of the output shaft is synchronized with the supply current. This means the integral number of AC cycles is equal to the rotation period. There are electromagnets on the stator of a synchronous AC gear motor, creating a magnetic field that rotates at the same time and frequency as the oscillations of the line current. The line current frequency and the number of magnetic poles determine the speed of a synchronous motor. Consequently, because this type of AC gear motor doesn’t rely on “slip,” torque is produced at a synchronous speed.

AC Asynchronous Motors

The AC asynchronous motor differs from the synchronous motor in that it runs a bit slower than the supply frequency. Electromagnetic induction supplies power to the rotor instead of slip rings or a commutator. Asynchronous motors are often brushless and use an alternating current that’s designed to create a rotating magnetic field. In this type of motor, the rotation of the rotor is slower than the stator field’s speed. As a result, the rotor’s windings are in closed-loop form, and the magnetic field that goes through the rotor changes. These magnetic fields react against the stator field, so the direction of the magnetic field is opposite of the current in the windings. While there is no slip in synchronous motors, the slip in asynchronous motors can vary between 1 and 6 percent. The AC induction motor is a common type of asynchronous AC gear motor and is the most rugged and simple type of electric motor. Sometimes the terms asynchronous motor and induction motor are used interchangeably.

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