Types of DC motors and why do we need DC motors

Introduction to DC motor

An electric motor is a machine which converts electrical energy into mechanical energy, DC motor is very similar to the DC generator. The difference between a DC motor and a generator is, the generated EMF is greater than terminal voltage in a generator while in case of a motor the EMF is less than the terminal voltage and thus the flow of the power is reversed a DC motor converts electrical energy into mechanical energy which is the reverse process of the generator



The working principle of a Dc motor is if a current carrying conductor is placed in a magnetic field then a mechanical force will be experienced which will be proportional to the current in the conductor the force direction is depended on Fleming’s left-hand rule so the conductor will move in the direction of the force

Why do we need DC motors

  • It converts electrical energy to mechanical energy
  • It gives constant mechanical power or constant torque
  • It can do rapid acceleration or deceleration
  • DC motors can be widely used as a positioning device because its speed and torque can be controlled over a wide range
  • Torque and speed characteristics of a DC motor can be varied for a wide range but it won’t affect the efficiency
  • It provides high starting torque
  • DC motors can be used in industrial equipment and machinery which can’t be easily run from remote power sources
  • It is the primary means of electric traction
  • DC motors are being used in adjustable speed machines
  • Precise voltage control can be done because it is directly connected to the field of the motor

Types of DC motor

  • Permanent magnet DC motors
  • Separately excited DC motors
  • Series wound DC motors
  • Shunt wound DC motors
  • Compound wound DC motors

Permanent magnet DC motor

In this type, the power supply is connected to the armature conductors and the magnetic field is produced by the permanent magnet which is mounted on the stator. this type is more advanced than the conventional dc motor like less operational cost and the direction of the rotation of the permanent magnet can be changed by reversing the two power lines

Separately excited DC motor


In this type of DC motor, it has field coils similar to those of a shunt wound DC motor and the supply is given separately to the field and the armature winding, the armature current does not flow through the field windings because the field coil and the armature coil are fed from a different power source

Series wound DC motor


In this type, the field winding is in series with the armature of the supply, if the mechanical load increases then the current will increase too and it will create a stronger magnetic field. The speed will vary very fast at no load and very slow at heavy load. The series motor produces high torque as the current pass through the low resistance field

Shunt wound DC motor


In this type the field coil is connected in parallel with the armature and the field winding consists of thin wire with a large number of turns, to provide large resistance, the field current is less than the armature current. Due to many turns of wire in the field winding strong electromagnetic force is produced

Compound wound DC motor

  • Cumulative compound wound
  • Differential compound wound

Cumulative compound wound


In this type, the field winding is connected in a way that the direction of the current is same in both the field windings and the flux created by the series field winding strengthens the field due to shunt field winding

Differential compound wound


In this type, the field windings are connected in a way that the flow of current is opposite to each other in both of the field windings. In this type, the flux due to the series field weakens that of the shunt field winding