DIRECT CURRENT MOTORS

are rotating machines built in a manner very similar to Direct Current Generators, but designed to convert electrical energy into mechanical energy. Like the Direct Current Generator which they so closely resemble and with which, in fact, they are interchangeable, these motors operate on the principles of electro-magnetic induction and Lenz’s law. They have been developed to a high degree of perfection and are used extensively to furnish the motive power for Electric cars, Trucks and many forms of power using machines. They are particularly adapted to applications where wide variations of speed are nece ary, such as printing pre es, lathes and various other machine tools. The speed of these motors is varied either by varying the strength of their magnetic fleld or by changing the voltage applied to the armature windings. A decreased field strength or an increased armature voltage causes the motor to run faster. However when the field. strength is decreased beyond a certain point the torque developed falls off rapidly, so that if further increase of speed is nece ary the voltage applied to the armature must be increased. Variation of the current flowing through the field magnets, resulting in variation of field strength, is generally sufficient for all ordinary purposes. See HEx.xecrnricrry.