An electric motor is a machine that converts electric energy into mechanical energy. An electrical signal (voltage) is applied to the input terminals of the motor, and the output of the motor output generates a specific torque according to the motor characteristics.
AC motors and DC motors perform the same function which is to convert electric power into mechanical power, however, they are powered, manufactured and controlled in a different manner. The most primary difference between two of them is the source of power. A.C. motors are operated with alternating current whereas DC motors are operated with direct current, like DC supplies, batteries, or AC-DC converters.
Here, the practical differences between AC and DC Motor are discussed on the basis of important factors like starting mechanism, efficiency, brushes & commutation, response to sudden load change, supply sources, stator & rotor action, speed & torque, armature location, maintenance and uses.The following table explains the key differences between AC and DC Motor.
Difference between AC Motor and DC Motor
| Characteristics | AC Motor (Induction) | DC Motor |
|---|---|---|
| Supply | Works on AC supply | Works on DC supply (mainly from batteries, and cells) |
| Starting | Needs starting mechanism for single phase NOT for three phase | Self-starting |
| Supply system | Can be single and three phase | Single phase ONLY |
| Stator & Rotor Action | Stator remains stand-still and supplies rotating field while rotor rotates | Armature rotates and field winding remains stand still |
| Brushes & Commutator | Do not have brushes and commutator; very rigged and have long life | Have brushes and commutator which limit the speed and reduce the life expectancy |
| Speed control | By changing frequency | By changing armature winding’s current |
| Speed & Torque | Use for high speed and variable torque | Use for variable speed and high torque |
| Load change | Slow response to change in load | Quick response to load change |
| Efficiency | Less efficient because of induction current loss and motor slip | More efficient since no motor slip and induction current loss |
| Armature Location | Armature remains Stationary and magnetic field rotates | Magnetic field remains stand still while armature rotates |
| Use | AC motors are primarily used in large industries and factories | They are used in most of the domestic applications. |
| Maintenance | Requires less maintenance because of absence of brushes and commutation process | Demands extensive maintenance frequently |
Conclusion
DC motors are typically utilized in applications where the speed has to be controlled by some external source. AC motors operate better in such applications where power efficiency is required for a longer time. AC motors are a single phase as well as three phase whereas DC motors are single phase always.
In certain applications, DC motors are substituted with an AC motor which is connected with an electronic speed controller. This connected assembly is called variable frequency drives (VFD). DC motors comprise of moving parts that are costly to replace, and repair is generally more expensive than utilizing an AC motor with an electronic controller.
