Page 338 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

Working Principle

An electrical machine that is used to convert the energy from electrical to mechanical is known as a DC motor.
The DC motor working principle is that when a current-carrying conductor is located within the magnetic field, then
it experiences a mechanical force. This force direction can be decided through Flemming’s left-hand rule as well
as its magnitude.
If the first finger is extended, the second finger, as well as the left hand’s thumb, will be vertical to each other
& primary finger signifies the magnetic field’s direction, the next finger signifies the current direction & the third
finger-like thumb signifies the force direction which is experienced through the conductor.
F = BIL Newtons
Where,

‘B’ is the magnetic flux density,
‘I’ is current
‘L’ is the conductor’s length in the magnetic field.
Whenever an armature winding is given toward a DC supply, then the flow of current will be set up within the
winding. Field winding or permanent magnets will provide the magnetic field. So, armature conductors will
experience a force because of the magnetic field based on the above-stated principle.
The Commutator is designed like sections to attain uni-directional torque or the path of force would have overturned
each time once the way of the conductor’s movement is upturned within the magnetic field. So, this is the working
principle of the DC motor.
Types of DC Motors

In order to appreciate the benefits of DC motors, it is important to understand the various types. Each type
of DC motor has beneficial characteristics that must be examined before purchase and use. Two of the main
advantages of DC motors over alternating current (AC) motors are how easy they are to install and that they
require little maintenance.
DC motors are differentiated by the connections between the field winding and the armature. The field winding
can be connected parallel to the armature or connected in a series. In some cases, the connection is both parallel
and in a series.

A further distinction of DC motors is how the rotor is powered; it can be brushed or brushless. In brush DC motors,
current is applied to the rotor by brushes. In a brushless DC motor, the rotor has a permanent magnet.
Since DC motors are everywhere and used for a wide variety of applications, there is a different type to meet the
needs of every application. Regardless of your need for DC motors, it is important to understand each type since
they can be found in every aspect of life.

Brushed DC Motor

The magnetic field in a brush DC motor is produced by current sent through a commutator and brush that are
connected to the rotor. Brushes are made of carbon and can be separately excited or self excited. The stator is
the enclosure that contains the components of the motor and contains the magnetic field. The winding of the coil
on the rotor can be in a series or parallel to form either a series wound DC motor or shunt wound DC motor.
The commutator is an electrical switch that reverses the current between the rotor and the external power source.
It is a method of applying electrical current to the windings and produces a steady rotating torque by reversing
the current direction. The sections of the commutator are attached to the windings on the rotor through a set of
contact bars that are set in the shaft of the motor.
There are three main types of DC motors: separately excited, self excited, or permanent magnet. In the separately
excited and self excited, an electromagnet is used in the stator structure. With the permanent magnet type, a
powerful magnet generates the magnetic field.
Self excited DC motors are further divided into shunt, series, and compound. The compound excited type is
separated into cumulative and differential with short and long shunts in each type.

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CITS : E & H - Electronics Mechanic - Lesson 205 - 222