Comparison of DC Motors

Comparison of DC Motors

A DC motor is widely used in different applications. In this article, we will discuss a comparison of DC motors. The DC motors are classified into three types;

  • Shunt Motor
  • Series Motor
  • Compound Motor

Shunt Motor

In the DC shunt motor, the field winding and armature windings are connected parallel.

The speed of a shunt motor is almost constant.

The starting current of a shunt motor is not high compared to the series motor for the same current input. Therefore, it is used in the application where we need almost constant speed from no-load to full-load.

Series Motor

In a DC series motor, the field winding and armature winding are connected in series.

Compared to a shunt motor, the series motor has high starting torque and has relatively good accelerating torque.

This motor has very high-speed variation in loading conditions. The speed of the motor is low at high load conditions and dangerously high at low load.

Therefore, DC series motor is used in high starting torque applications like driving hoists, cranes, etc.

The DC series motor is unsuitable for the application where the load decreases to a specific small value. Hence, it is not eligible for belt drive applications and centrifugal pumps.

Compound Motor

Two field windings are used in the DC compound motor. one is the series field winding, and the second is shunt field winding.

If the series flux is in the same direction as shunt flux, this type of connection is known as a cumulative compound motor.

If the series field opposes the shunt field, then the motor is known as a differential compound motor.

Comparison of DC Motors

The torque vs armature current and Speed vs armature current characteristic is shown in the figure below.

Characteristic of DC Motor
Characteristic of DC Motor

According to applications and performance characteristics, users choose which motor is suitable.

The below table shows a summary comparison of DC motors.

Type of DC Motor Characteristic Applications
DC Shunt Motor Speed slightly changes as the load varies from no-load to full load.

Approximately constant flux and speed.

Torque is directly proportional to the armature current.

This motor has medium starting torque (up to 1.5 times of full-load torque).

They were used in the applications where medium starting torque is required.

Centrifugal Pumps



Lathe machines


Spinning machines

Most suitable for belt-driven applications

Reciprocating pumps

DC Series Motor Speed is inversely proportional to the torque.

Very high starting torque (square proportional to the armature current) (T ∝ Ia).

Speed of DC series motor is variable.

Adjustable, varying speed

Electric Traction



Trolley cars



DC Compound Motor The characteristics of DC compound motor lie between DC series and shunt motors.

The Shunt field provides constant speed, and the series field provides high starting torque.

It is widely used in high torque applications.

This motor is further classified into two types; Differential compound and Cumulative compound.

Adjustable, varying speed

The differential compound motor is rarely used. In most applications, a cumulative compound motor is used.


Shearing machine

Air compressor

Reciprocating machine

Rolling machines

Printing press

Ice machines

Heavy planners


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