Rectifying Action of a Commutator:

The armature windings of a DC generator produce an AC voltage. To obtain a unidirectional (DC) voltage at the output terminals, a commutator is used. The commutator consists of multiple copper segments insulated from each other and mounted on the shaft. The ends of the armature coils are connected to these segments. Carbon brushes rest on the commutator, making contact with different segments as the commutator rotates.

As the armature rotates, the voltage induced in each coil alternates. However, the commutator segments are arranged such that when the voltage in a coil reverses, the brushes switch to contact a different set of commutator segments, connected to the coil's opposite ends. This switching action effectively reverses the coil's connections to the output terminals, thereby rectifying the alternating voltage into a pulsating direct current.

In a simple DC generator with a single coil, the output voltage would be highly pulsating. To achieve a smoother, more uniform DC output, multiple coils and commutator segments are used. The coils are arranged around the armature such that their voltages add up to produce a relatively constant output voltage, even with a pulsating waveform. The more coils and segments, the smoother the DC output becomes. This smoother output is a result of the commutator's continuous switching action between different coil windings as they pass through their peak AC voltages. The brushes are strategically positioned at the neutral points on the commutator, minimising sparking and ensuring smooth current flow.