[Physics Class Notes] on Difference Between AC And DC Motor Pdf for Exam

Points of Difference

AC Motor

DC Motor

Current Input

When an alternating current (AC) is passed as an input, then only the AC motor works.

Dc operates when Direct Current supply is provided. The motor might operate with AC power supply in the DC series motor. However, for shunt motors, DC supply is necessary.

Motor Starting

A single-phase AC motor needs a starting procedure. However, a three-phase AC motor requires no starting mechanism as it is self-starting.

It’s the main difference between AC and DC motors that later one is always self-starting. 

Input Terminals

Three input terminals are present in these motors.

Two input terminals that are; positive and negative exist in DC motors.

Types 

There are two types of AC motors, i.e., Synchronous AC motors plus Induction AC motors.

There are mainly two types of DC motors, namely; DC motors with brushes and without brushes.

Armature Characteristics

The armature is fixed in this type of motor, and the magnetic field rotates.

The magnetic field remains constant, and the armature rotates in DC motors.

Load Change

To the variable load, these motors don’t show a fast response. 

AC DC motor difference is that DC motors show a rapid response to the load change.

Commutators 

AC motors don’t contain commutators.

DC motors comprise commutators.

Brushes 

Like commutators, brushes are also absent in these motors. 

These motors involve carbon brushes. 

Life Expectancy 

Due to the absence of commutators and brushes, AC motors have a high life expectancy. 

The presence of commutators as well as brushes restricts the speed of these motors. Hence, it lessens the life expectancy of the DC motor. 

Speed Control

By changing the frequency, it’s easy to change the speed of an AC motor.

By varying the armature winding current, it’s easy to control the speed of DC motors.

Maintenance

Due to the nonappearance of commutators and brushes, AC motors require low maintenance. 

Due to the presence of commutators and brushes, DC motors require high maintenance.

Input Supply Phases

These motors can work on both single and three-phase supplies. 

DC motors work only when there is a one-phase supply. 

Applications 

Whenever there is a requirement for rapid speed or inconstant torque, these motors are preferable. 

When there is a requirement for changing speed or high torque, these motors are preferable.

Uses 

AC motors are commonly used in bulky industry productions.

DC motors are commonly used in minor domestic purposes. 

Efficiency 

The efficiency of AC motors is often less. It’s because of the motor slip and induction current loss. 

There is not any loss in the induction current or magnetic slip. Hence, DC motors have high efficiency.