Question

What is the process for reversing a DC motor?

Answer 1

The direction of rotation of a DC shunt motor can be reversed by changing the polarity of either the armature coil or the field coil.

The best way is to reverse the shunt coil as it take less current than armature, you can use a dual two positions switch, let´s put both coil ends on mid points and plus/minus VCC on each position but reversed so the field coil will be reversed whenever the switch is toggled

.If you can get to separate rotor and stator windings, you reverse one of the windings, that reverses the magnetic field and the direction of rotation reverses. You have to make sure the motor is designed for that, some have unidirectional mounting of the brushes and they don't work well in the opposite direction.

thus-

• For a permanent magnet DC motor - just reverse the polarity of the supply voltage.
• For a “standard” brushed DC motor, it is easiest to do on a separately excited motor, where the field winding has separate terminals to the (main) armature winding. This is typically done on a motor designed for speed control. To reverse the motor, you need to change the polarity of the supply voltage to either the field winding or the armature winding, but not both. Generally it is better to reverse the field voltage because the field current is less than the armature current, so your reversing switchgear is more lightweight. If you cannot separate the field terminals and armature terminals, then reversing cannot be done.
• For a brushless DC motor, reversing the supply polarity won’t work and will possibly damage the motor. The electronic commutation needs to be reversible, which has to be part of the motor design.

:We cannot change the direction of shunt motor by changing the supply terminals.