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AC and DC motor

This article will highlight the difference between AC and DC motor.

AC and DC motors are two different types of motors. However, they do have a lot in common such as electrical power and friction. The difference between them is the way that power is delivered to the motor. In an AC motor, power flows constantly through the motor coils and creates its magnetic field which pushes on a permanent magnet that rotates inside a stator to create motion or rotational energy.

What is AC Motor?

An AC motor is a type of motor that can deliver electricity to the windings inside the stator without interruption while the AC power is flowing through them. It converts mechanical energy into electrical energy and then transfers electricity back into mechanical energy. This process is known as electromagnetic induction or electromagnetic force. If you compare an AC motor with a DC motor, you’ll find that an AC motor has coils of copper wire wrapped around a magnetic core whereas DC motors have no coils and have no magnetic parts.

What are the properties of an AC Motor?

1) High efficiency: The efficiency of an AC motor depends on its overall design as well as its main components such as shaft speed, voltage, power, torque, etc.

2) Long life: Unlike DC motor that suffers power loss due to internal friction, AC motor has no physical parts so there is no motor temperature and wear limit.

3) Low noise: Compared to a DC motor, AC motors are quieter.

4) High RPM output: The RPM of an AC motor is high than the DC motor because it uses magnetic coupling unlike that of the mechanical transmission of a DC motor which transfers energy by moving parts.

5) Long starting torque: The starting torque is high in an AC motor compared with a mechanical transmission of a DC engine wherein there are rotating parts. What is an Inverter?  Inverter play important role in an electric appliance like refrigerator, television and other similar equipment.

What is DC Motor?

A DC motor is a type of electric motor in which the flow of electric current is constant and the direction of current flow is reversible.

What are the properties of a DC Motor?

1) Low weight: DC motors are lighter in weight than AC motors because they do not contain coils.

2) Low cost: DC motors are less expensive to manufacture as they require less copper wire and iron.

3) High starting torque: The starting torque of a DC motor is high in comparison with an AC motor.

4) low efficiency: The efficiency of a DC motor depends on its RPM, speed, power, and friction loss properties.

5) Less maintenance requirement: You don’t need to change the brushes or the commutator unlike AC motor.

Differences between a DC and an AC motor are:

  1. Mechanism: An AC motor moves due to the interaction between electromagnetic force and the magnetic field created by the permanent magnets in it. Whereas, the moving force in a DC motor comes from the interaction between electromagnets and steel pieces (permanent magnets) placed over them. DC motors are easy to control, but their rotational speed depends on the applied voltage and load. On the other hand, AC motors have high starting torque, but they can be controlled more easily with variable resistors.
  2. Temperature: The temperature of an AC motor is high because of the heat created from friction and also from the manipulation of electrical current. But a DC motor generates very low heat as compared with an AC motor.
  3. Type of power: In comparison to an AC motor, a DC motor requires no physical parts such as coils or magnetic materials in it. It uses electromagnets which act like huge electrostatics capacitors in that they can store and release energy very rapidly, which is essential for a DC motor to have high torque at very high speeds. Also, magnets used in a DC motor are permanently fixed together and they do not move relative to each other while they rotate in a stationary stator. On the other hand, electromagnets in an AC motor are temporary magnets that move relative to each other in the rotor.
  4. Inverter: In an AC motor, the electromagnetic current is interrupted between each circuit as it passes through the magnetic circuits. But, in a DC motor, there is no such interruption between each circuit so that electricity can continuously flow within them. That is why you don’t need to turn off lights or any appliances when you are done with them.
  5. Permanent: As different electrical appliances use various amounts of power at different rates, it’s not possible to have a permanent electric source that delivers constant voltage and current. But, when you use a DC motor with a permanent magnet, it can be connected to a transformer that converts the voltage to higher or lower and the current can be adjusted. In other words, if you have applied voltage of 120VAC and a household appliance uses 60W of power but operates at 60VAC, you can connect your large loads such as refrigerators and air conditioners to the motor.
  6. Control: AC motors are controlled by electronic relays while DC motors are controlled by electronic sensors.
  7. Transformer: A transformer is an electrical device that changes AC voltage into low or high-frequency AC voltage.

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In this article, we have covered the difference between a DC and an AC motor. It is necessary to know the difference between these two motors to select the right type for your application. We may also face some problems in choosing DC or AC Motors because of their similarities. In those cases, if we want to choose a motor for a specific purpose, first make sure that you need similar characteristics from both of them.

For example, if you want to choose a high starting torque motor then you can consider both of them but if you want one with long life then do not consider an AC motor. It is also important that before buying a motor or other electric products make sure that it has approval for use in your country/region.


Frequently asked questions

Get answers to the most common queries related to the JEE Examination Preparation.

What is the speed of a DC motor?

Answer. The rotational speed of a DC motor is controlled by voltage.

What is the main difference between an AC and a DC motor?

Answer. An AC motor converts electrical energy into mechanical energy and vice versa. But, in a DC motor, the curren...Read full

What are the characteristics of an AC Motor?

Answer. The characteristics of an AC Motor include high efficiency, high starting torque, low maintenance requiremen...Read full

What are the characteristics of a DC Motor?

Answer. The characteristics of a DC Motor include a permanent magnet, lower weight, low cost, long life, etc....Read full

Can you name some applications of an AC motor?

Answer. An AC motor can be used in commercial and residential buildings to drive fans, lights, and heating appliance...Read full