DC Motor -principle-construction

What is DC Motor?

A machine that converts dc electrical energy into mechanical energy is known as DC Motor.

Principle of DC Motor

Its operation is based on the principle that when a current-carrying conductor is placed in a magnetic field, the conductor experiences a magnetic force(or torque). The direction of the magnetic force is given by Fleming's Left-Hand Rule.

It states that when the thumb, middle finger, and index finger are extended mutually perpendicular to each other and if the index finger points the direction of the magnetic field and the middle finger points the direction of current then the thumb represents the direction of force experienced by the magnetic field on the shaft of dc motor.

Construction of a dc motor

• A simple dc motor consists of a rectangular coil that is placed in a magnetic field.

• This magnetic field is provided by permanent magnet or electromagnets.

• Two ends of the coil are connected to two slip rings.

• When the coil is rotated a flux is linked with the coil, which induced a current 

• This current is bi-directional.

• To make this current uni-directional we replace the slip rings with splits rings.

• The position of the brush is arranged in such a way that the connection of brushes with the coil is being exchanged with each other.

• When the coil is perpendicular to the lines of the magnetic field, the induced emf is zero.

Parts of DC Motor

• Armature        

• Commutator

• Brushes

• Axel

• Permanent Magnet

• DC Power Supply

1. Armature

• An armature is the main component, it contains an armature coil 

• it provides the path of low reluctance from pole to pole (North to South).

• It may be cylindrical in shape.

• It is made up of circular steel lamination.

• Its laminations are attached to the rotating shaft known as a rotor.

2. Commutator

• The commutator collects the current from armature conductors.

• it converts the induced armature current into the uni-directional current.

• it is made up of copper.

• it is made in a wedge shape.

• it is also known as split rings

3. Brushes

• the function of the current is to collect current from the commutator.

• generally made up of carbon and graphite.

• Mostly it is shaped like rectangular blocks.

• These brushes are placed in the brush holders.

• they are made to hold the commutator with the help of spring.

Types of DC Motors

• Shunt-wound dc motor

• Series-wound dc motor

• Compound-wound dc motor