Direct Current (dc) Generators
An AC generator can be modified to produce direct current (DC) electricity also. The change requires a commutator. A commutator is simply a slip ring that has been cut in half, with both halves insulated from each other. The brushes attached to each half of the commutator are arranged so that at the moment the direction of the current in the coil reverses, they slip from one half of the commutator to the other. The current that flows into the external circuit, therefore, is always traveling in the same direction.
Macaulay, David. The New Way Things Work. Boston: Houghton Mifflin Company, 1998.
McGraw-Hill Encyclopedia of Science & Technology. 6th edition. New York: McGraw-Hill Book Company, 1987, vol. 7, pp 635-37.
David E. Newton