A simple Ac generator consists of: a strong magnetic field, conductors that rotate through that magnetic field, and a means by which a continuous conection is provided to the conductors as they are rotating. The strong magnetic field is produced by a current flow through the field coil of the rotor. The field coil in the rotor receives excitation through the use of slip rings and brushes. Two brushes are spring-held in contact with the slip rings to provide the continuous conection between the field coil and the external excitation cicuirt