How AC Motors Work

By Tyler Lacoma, eHow Contributor

 
 
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1. Motors

   • The purpose of a motor is to create motion. Motors can be part of vast engines or very small devices that power simple tools, but all motors work based on the principles of magnetism. If you looked at the inside of any motor, you would see a fairly simple device created from an armature, or simple metal rod, a coil of wire, and probably surrounding coils or encasements known as the stator.

     These devices together create warring magnetic fields. In simple motors, one magnetic field is created through the use of permanent magnets, while the other field is created by sending an electric current through the coil of metal on the armature, making an electromagnetic field. Large motors use two electromagnetic fields. As the fields push off each other, the armature spins, creating the basic turning motion of the motor. The force it spins at is known as the torque of the motor. All motors work in this basic fashion, but they differ in terms of size, complexity and application.

   AC and DC Current

   • Motors that run on batteries or use fuel from engines do not need to worry about alternating current, or AC--the DC electricity simply creates a constant magnetic field. However, AC electricity comes in alternating waves, which makes it difficult to create the stable magnetic fields necessary for creating a smooth motor motion. In traditional motors, this problem is solved by using very exact materials and regulators to ensure that the motor runs at the frequency of the sine wave on which the electrical current is traveling. The currents going to the different parts of the motor need to be aligned precisely in order to achieve a stable force.

   AC Induction Motors

   • Many AC motors are induction motors, in which the electrical current is induced in the motor rather than directly channeled to it. This is a complicated process, and many components are needed to keep the motor running, but essentially the magnetic force is applied only to one of the electromagnetic fields, which then moves the other field, creating the current and force necessary for the motor to turn. This is a little like pushing the wagon to start the horse, but works well for smaller motors found throughout the home. The key is to create a strong enough starting force for the motor to pick up speed and generate torque. This means that AC induction motors require a sharp burst of power when first starting, and do not generate as much power as a DC motor. However, they also tend to be quieter and cheaper than other motors.

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