Series AC Motor

A series ac motor is the same electrically as a dc series motor. Refer to the illustration below and use the left-hand rule for the polarity of coils. You can see that the instantaneous magnetic polarities of the armature and field oppose each other, and motor action results.

Now, reverse the current by reversing the polarity of the input. Note that the field magnetic polarity still opposes the armature magnetic polarity. This is because the reversal effects both the armature and the field. The ac input causes these reversals to take place continuously.

Series ac motor .

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The construction of the ac motor differs slightly from the dc motor. Special metals, laminations, and windings are used. They reduce losses caused by eddy currents, hysteresis, and high reactance. Dc power can be used to drive an ac motor efficiently, but the opposite is not true.

The characteristics of an ac motor are similar to those of a dc motor. It is a varying-speed machine. It has low speeds for large loads and high speeds for light loads. The starting torque is very high.

Series type motors are used for driving fans, electric drills, and other small appliances. Since the ac motor has the same general characteristics as the series dc motor, a series motor has been designed that can operate both on ac and dc. This ac/dc motor is called a universal motor. It finds wide use in small electric appliances.

Universal motors operate at lower efficiency than either the ac or dc series motor. They are built in small sizes only. Universal motors do not operate on polyphase ac power.

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