# Direction of Rotation of DC Motor

Direction of rotation of DC Motor can be reversed by reversing the direction of torque of the motor. When motor exerts torque in clockwise direction it rotates in the clockwise direction and when the motor exerts torque in anti clockwise direction, the motor rotates in the anti clockwise direction. Thus, the direction of the DC motor can be reversed by reversing the direction of the torque.

The direction of the force experienced by armature conductor can be known by Fleming’s left hand rule.

The force experienced by armature conductor is

F = B l  I    Newton (N)
B = Flux density due to the flux produced by the field winding.
l  = Active length of the conductor.
I = Magnitude of the current passing through the conductor.
The direction of force can be reversed by changing the direction of magnetic flux or armature current. With change in direction of force the direction of torque also gets reversed.

The torque equation of the DC motor is expressed by following mathematical formula.

From equation(1) it is clear that the magnitude and direction of DC motor torque depend on the followings.

1, Flux/Pole
2. Armature Current

The direction of the torque can be reversed by reversing the direction of the flux or by reversing the direction of the armature current. The direction of the flux can be changed by reversing the direction of the field current. If the direction of the field current and armature current both is changed the motor direction will not change.
Thus, direction of rotation of DC Motor can be reversed in different DC motors as given below.

In the case of separately excited DC motor and shunt DC motor, the direction of the motor can be changed by reversing the direction of either field current or armature current.

In the case of series DC motor, the direction of the motor can be changed by reversing the polarity of the either field coil or armature coil.

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