How does a DC generator produce direct current?

A DC generator converts mechanical energy to electrical energy. When a conductor rotates in a magnetic field, EMF is induced (Faraday's law). The commutator with brushes rectifies the AC generated in the armature to DC at the terminals. EMF generated depends on flux, speed, and number of conductors: E = (P x phi x N x Z)/(60 x A). Different excitation methods (separately excited, shunt, series, compound) provide different voltage-current characteristics.