A commutator reverses the direction of the current that travels from the rotor to the external circuit of an electrical generator or electric motor. Commutators have multiple metal brushes that make contact with the external circuit.
By reversing the direction of the current in the moving coil of a rotating machine, the commutator achieves a steady amount of torque production from an electric motor. When used as part of an electrical generator, a unidirectional current to an external circuit is achieved. A commutator was first used in an early alternating current generator in 1832 by the French instrument maker Hippolyte Pixii. The addition of the commutator changed the output of Pixii's device to direct current.