DIFFERENCE BETWEEN AC AND DC MOTORS

Commonly ran by an AC variable frequency drive, an AC electric motor operates by applying alternating current (AC) power to the electric motor. An AC electric motor consists of several parts but the main parts are the stator and rotor.

The AC electric motor’s stator has coils that are supplied with the alternating current and produces a rotating magnetic field. The AC electric motor’s rotor rotates inside the electric motor’s coils and is attached to an output shaft that produces torque by the rotating magnetic field. There are two different types of AC electric motors and each of them uses a different type of rotor. The first type of AC motor is called an induction motor (also known as an asynchronous motor).

An induction motor uses a magnetic field on the rotor of an induction motor that’s created by an induced current. The other type of AC motor is called a synchronous motor and rotates precisely at the supply frequency or on a sub-multiple of the supply frequency.

A synchronous motor is able to operate with precision supply frequency because it doesn’t reply on induction. The magnetic field on a synchronous motor is generated by current delivered through slip rings or a permanent magnet. Synchronous motors run faster than induction motors because the speed is reduced by the slip of the asynchronous motor.

DC ELECTRIC MOTORS

DC electric motors are powered from direct current (DC) power and are mechanically commutated machines. DC electric motors have a voltage induced rotating armature winding, and a non-rotating armature field frame winding that is a static field, or permanent magnet.

DC electric motors use different motor connections of the field and armature winding to produce different speed and torque regulation. Unlike AC electric motors, DC electric motor speed can be controlled within the winding by changing the voltage applied to the DC motor armature, or by adjusting the field frame current.

Most DC electric motors today are manufactured to be controlled with industrial electronic DC drives. DC electric motors are still used in many applications across the globe such as paper producing machines, and steel mill rolling machines.

CONCLUSION

DC motors are usually seen in applications where the motor speed needs to be externally controlled. AC motors work best in applications where power performance is sought for extended periods of time. All DC motors are single phase, but AC motors can be single phase or three phase.

AC and DC motors use the same principle of using an armature winding and magnetic field except with DC motors, the armature rotates while the magnetic field doesn’t rotate. In AC motors the armature does not rotate and the magnetic field continuously rotates.

In some applications today, DC electric motors are replaced by combining an AC electric motor with an electronic speed controller, known as variable frequency drives. DC electric motors are replaced with an AC electric motor and an electronic speed controller because it is a more economical and less expensive solution.

DC electric motors have many moving parts that are expensive to replace, and DC electric motor repair is usually more expensive than using a new AC electric motor with an electronic controller.

THEMOST COST EFFECTIVE SOLUTION

You can save thousands of dollars by switching from three phase DC to AC motors. AC Motors now own the majority of the market share, driving down costs. AC Variable Frequency Drives such as the ones we sell at our web store give complete control over the speed and power consumption of an AC Motor.

In our experience, combining an AC motor and drive proves to be the most cost effective solution for mostapplications. When servicing our customers in the field, we often recommend looking at the SMVector Series Variable Frequency Drive in combination with a three phase AC motor.