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Difference between AC and DC Motor
In this article, we will take a detailed look at the various features of AC and DC motors and highlight their differences. An electric machine that converts electrical energy (either AC or DC) into mechanical energy is known as an electric motor. Based on the type of input electric supply, electric motors are classified into two types, viz. −
- AC Motor
- DC Motor
What is an AC Motor?
An AC motor is one that converts AC electrical power at input into mechanical power at output by using the principle of electromagnetic induction. The AC motor takes alternating current as the input. It consists of two main parts viz. stator and rotor. The stator is the stationary part of the motor and the armature winding is placed on the stator while the rotor is the rotating part of the motor. AC motors are further classified into two types as −
- Single-phase AC motor
- Three-phase AC motor
What is a DC Motor?
A type of electric motor that takes direct current (DC) as the input electrical energy and converts this DC electrical input into mechanical (rotational) output is known as DC motor. In simple words, an electric motor which converts direct current electrical energy into mechanical energy is known as DC motor.
A DC motor has two main parts viz. stator and rotor. The stator is the stationary part of the motor and carries magnetic field system while the rotor is the rotating part and has armature winding, for this reason, the rotor of the DC motor is also called armature.
The DC motors come in different sizes and power ratings, from the small motors used in toys to large mechanisms like power vehicles.
Difference between AC and DC Motor
The following table gives the important difference between the AC motors and DC motors.
| Point of Comparison | DC Motor | AC Motor |
|---|---|---|
| Definition | DC motor is the electric motor which converts direct current electrical energy into mechanical energy. | AC motor is the one that converts input AC electrical energy into mechanical energy. |
| Nature of input current | Direct current is the input electric current in the DC motors. | Alternating current is the types of input electric current in the AC motors. |
| Sources of supply | The main sources of supply for DC motors are DC generator, battery, cells, etc. | Three phase or single phase power supply is obtained from the supply mains. |
| Process of commutation | The process of commutation (conversion of input DC into AC) is present in case of DC motors. | There is no commutation process in the AC motors. |
| Number of supply phase | In DC motors, only single-phase supply is used. | In AC motors, both single-phase supply and three-phase supply are used. |
| Number of input terminals | In DC motor, there are two input terminals viz. positive terminal and negative terminal. | In case AC motor, there are two input terminals in a 1-phase AC motor (viz. line and neutral) and three terminals (viz. R,Y, B) in case of a 3-phase AC motor. |
| Position of armature | In a DC motor, the armature winding is placed on the rotor, i.e. DC motor has rotating armature. | In case of an AC motor, the armature is placed on the stator, i.e. AC motor consists of a stationary armature. |
| Type of magnetic field | In a DC motor, the magnetic field remains stationary and the magnetic field system is placed on the stator. | AC motors have rotating magnetic field and this rotating magnetic field is produced by the AC supply fed to the stator armature winding. |
| Use of carbon brushes | The carbon brushes are used in the DC motors. The carbon brushes are provided to connect the stationary input DC supply to the rotating armature winding. | There is no carbon brushes used in the AC motors. |
| Starting of motor | DC motors are the self-starting motors. | A 3-phase AC motor is self-starting while the 1-phase AC motor requires some starting mean. |
| Speed control | The speed of a DC motor can be controlled either by changing the armature current or field current. | The speed of AC motor is controlled either by changing the supply frequency or number of field poles in the motor. |
| Response to load change | The DC motor shows the quick response to the variation in the load. | AC motor shows the slow response to the variation in the load. |
| Lifespan | The use of commutator and brushes reduce the life span of a DC motor. | As the AC motor does not use the commutator and brushes, thus, their lifespan is longer. |
| Efficiency | Due to the absence of slip and induction current losses, the DC motors have higher efficiency. | The efficiency of the AC motor is low because of the presence of slip and induction current losses. |
| Maintenance and Maintenance cost | DC motors require frequent maintenance due to the presence of commutator and brushes. Therefore, their maintenance cost is high. | There is no commutator and brushes in the AC motors, thus, they require little maintenance and therefore, the maintenance cost is low. |
| Applications | DC motors are mainly used in variable speed and high torque applications, such as lifts, cranes, traction, etc. | AC motors are suitable for applications where high speed and variable torque is required. |
Conclusion
From the above discussion, it can be seen that there are various differences between AC and DC motors. Both of these motors are extensively used in various applications. Hence, the knowledge of these differences can help an individual to select either of them according to the requirements.
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