In many cases, the commutator is an annular sliding contact that rotates with the axis of the motor. Current reversal occurs by dividing the sliding contact into plates with corresponding circuits to the partial windings. Power is supplied by brushes that are pressed onto the commutator. These are usually made of copper graphite; precious metals are used in special cases. Mechanical commutation is thus available in two different versions: precious metal commutation and graphite commutation.
Precious metal commutation
The term "precious metal commutation" refers to the materials, consisting of high-performance precious metal alloys, which are used in the brushes and commutator. This type of commutation system is mainly used on account of its compact size, the extremely low contact resistance and the precise commutation signal. The commutation system is particularly suitable for applications with low current load, e.g., battery-powered devices.
The term "graphite commutation" or copper graphite refers to the used brush material in combination with a commutator made of a copper alloy.
Compared to precious metal commutation, graphite commutation is significantly more robust and can tolerate higher currents. Thus, it is better suited to dynamic high-performance applications with fast start/stop operation or periodic overload conditions.