In our previous post, we learnt about the basics of an electric motor. We saw how it works and which components work together to make it work. While both work for the same end result, i.e. to produce rotating magnetic field to in turn generate rotational mechanical force in the armature. In this post, we will see the difference between an AC and a DC motor. We recommend you read the basics first and then learn the differences between these two.
We have made prepared the differences in a tabular form for easy understanding.
Difference between an AC and a DC Motor:
| Differentiating Property | AC Motor | DC Motor |
| Current Input/Power Source | An AC Motor works only when alternating current is supplied to it as input. | A DC Motor on the other hand runs only when the supply provided to it is direct current. This is true for shunt motors. A catch here is that when the motor is a DC series motor, it can operate with an AC supply. |
| Types | AC Motors are primarily of two types- Induction motors and synchronous AC motors. | DC Motors are of two types as well. These are- with brushes and without brushes. |
| Construction | AC motors are complex in their construction as they have to have an alternating current winding in them. | DC Motors on the other hand have simple construction with direct current winding. |
| Input Supply Phases | AC Motors are capable of running on both single and three-phase supply | DC Motors run on single-phase supply only. |
| Starting of Motor | A single-phase AC Motor starts by itself but a three-phase AC motor requires a starting mechanism. | DC Motors are self-starting. |
| Armature Characteristics | In case of an AC Motor, the armature is fixed and what rotates is the magnetic field. | A DC motor on the other hand has a constant magnetic field and the armature rotates in this case. |
| Input Terminals | Irrespective of the type of AC Motor, it always has a three-input terminal. A three-phase input terminal is also known as RYB terminal as R stands for Red, Y for Yellow and B is for Blue. | Only two terminals are present in DC Motors. These are positive and negative terminals. |
| Speed Control | It’s quite easy to change the speed of an AC Motor as all that is needed is change is frequency, and the job is done. | Changing the speed of a DC Motor requires changing the armature winding current. |
| Load Change | These motors react slowly much to the change in load. | A DC motor, however, is quick in responding to varying loads. |
| Life Expectancy | Since there are no brushes or commutators, an AC motor has a high life expectancy. | A DC motor has a reduced life expectancy as the brushes and commutators restrict its speed, thus reducing its life. |
| Efficiency | Due to the reasons like motor slip and induction current loss, the efficiency of an AC Motor is usually quite less. | There is no slip or current loss in case of DC motors, and hence, they are significantly more efficient than their AC counterpart. |
| Maintenance | Lack of brushes and commutators means easier maintenance. | DC motors require high maintenance due to the presence of brushes and commutators. |
| Applications | AC Motors are commonly used where there is a need for high speed and variable torque. | DC Motors are commonly used where the speed keeps changing and the torque is high. |
| Practical Uses | These are generally used in heavy industry production lines. | These are widely used for domestic products. |
