A DC motor field coil is a non-moving part on which winding is wound to produce a magnetic field. This electro-magnet has a cylindrical cavity between its poles.
Commutator
The commutator of a DC motor is a cylindrical structure that is made of copper segments stacked together but insulated from each other using mica. The primary function of a commutator is to supply electrical current to the armature winding.
Brushes
The brushes of a DC motor are made with graphite and carbon structure. These brushes conduct electric current from the external circuit to the rotating commutator. Hence, we come to understand that the commutator and the brush unit are concerned with transmitting the power from the static electrical circuit to the mechanically rotating region or the rotor.
In the previous section, we discussed the various components of a DC motor. Now, using this knowledge let us understand the working of DC motors.
A magnetic field arises in the air gap when the field coil of the DC motor is energised. The created magnetic field is in the direction of the radii of the armature. The magnetic field enters the armature from the North pole side of the field coil and “exits” the armature from the field coil’s South pole side.
The conductors located on the other pole are subjected to a force of the same intensity but in the opposite direction. These two opposing forces create a torque that causes the motor armature to rotate.
Working principle of DC motor
When kept in a magnetic field, a current-carrying conductor gains torque and develops a tendency to move. In short, when electric fields and magnetic fields interact, a mechanical force arises. This is the principle on which the DC motors work.
Similar Reading
DC Generator
AC Generator
Universal Motor
DC motors have a wide range of applications ranging from electric shavers to automobiles. To cater to this wide range of applications, they are classified into different types based on the field winding connections to the armature as:
Now, let us discuss the various types of DC Motors in detail.
In self-excited DC motors, the field winding is connected either in series or parallel to the armature winding. Based on this, the self-excited DC motor can further be classified as:
In a shunt wound motor, the field winding is connected parallel to the armature as shown in the figure.
In a series wound DC motor, the field winding is connected in series with the armature winding as shown in the figure.
DC motors having both shunt and series field winding is known as Compound DC motor, as shown in the figure. The compound motor is further divided into:
In a cumulative compound motor, the magnetic flux produced by both the windings is in the same direction. In a differential compound motor, the flux produced by the series field windings is opposite to the flux produced by the shunt field winding.
In a separately excited DC motor, the field coils are energised from an external source of DC supply as shown in the figure.
A brushless DC motor, also known as synchronous DC motor, unlike brushed DC motors, do not have a commutator. The commutator in a brushless DC motor is replaced by an electronic servomechanism that can detect and adjust the angle of the rotor.
A brushed DC motor features a commutator that reverses the current every half cycle and creates single direction torque. While brushed DC motors remain popular, many have been phased out for more efficient brushless models in recent years.
The applications of different types of DC motors are listed below:
Owing to the fairly constant speed and medium starting torque of shunt DC motors, they are used in the following applications:
Owing to the high starting torque and variable speed of series DC motors, they are used in the following applications:
Owing to the high starting torque of cumulative compound DC motors, they are used in the following applications:
Frequently Asked Questions on DC Motor
Q1
Yes, the DC series motor runs on single-phase AC supply. This is because the torque, which varies as the product of the armature and field current, is always positive. Thus, a positive average torque causes the motor to rotate.
Q2
A universal motor is a special type of motor that can run on either DC or single-phase AC supply.
Q3
Q4
William Sturgeon invented the first DC motor in 1886.
Q5
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