Split-ring commutator

A simple direct-current motor uses a split-ring commutator attached to the rotating coil. Two stationary brushes press against its two halves, carrying current from the supply into and out of the coil. As the coil passes the vertical position, each half-ring changes which brush it touches.

A simple d.c. motor avoids this with a split-ring commutator attached to the coil. Stationary conducting brushes connect the d.c. supply to the two halves of the ring. As the coil passes each half-turn, the ring swaps which brush contacts each end of the coil.

A simple direct-current motor solves this using a split-ring commutator. Each half of the ring is connected to one end of the coil. As the coil reaches the position where its turning effect is zero, it briefly loses its electrical connection but continues moving because it is already rotating.

A split-ring commutator swaps the connections to the external circuit at each half-turn, just when that reversal occurs. The two reversals cancel at the output: the same external terminal stays positive, so current through a complete external circuit keeps flowing in one direction.