Problems With Practical AC Motors

While efficient and durable, AC motors also have drawbacks.

While air conditioning (AC) motors are among the most efficient, durable and practical machines ever invented, their designs also involve drawbacks and compromises. Most of these problems stem from using the single-phase AC power found in most homes.

Starting Torque

To begin running from a dead stop, a motor needs to overcome friction and other loads. Torque is the force with which the motor overcomes these loads. Most single-phase AC motor designs have weak starting torque. Starting capacitors and other assistive devices give the motor a brief energy burst helping it come up to speed.

Speed

A simple AC motor's speed depends on the power line frequency and the number of coil windings inside the motor. Unless an engineer adds complex electronic controls to the motor, this means it runs at a single, fixed speed.

Slip

Some AC motors lose speed when you increase their load. They are not locked to the AC main's frequency, but rather are pulled along by it. As load increases, the deviation from the ideal speed also increases. Engineers call this behavior "slip."

References

• Georgia State University: AC Motors and Generators
• University of South Wales: Electric Motors and Generators