A DC motor is a rotating device that converts DC electrical energy into mechanical energy. The motor stator provides a magnetic field, and the DC power supply provides current to the rotor windings. The commutator keeps the rotor current and torque generated by the magnetic field in the same direction. DC motors can be divided into two categories based on whether they are equipped with commonly used brush commutators, including brush DC motors and brushless DC motors.

A direct current generator is a machine that converts mechanical energy into direct current electrical energy. It is mainly used as a DC motor for DC motors, electrolysis, electroplating, smelting, charging, and excitation power supply for alternators. Although power rectifier components are also used to convert AC power into DC power in places where DC power is required, in terms of some operating performance, AC rectifier power cannot completely replace DC generators.