DC Motors operate on Direct Current. The primary advantage to DC Motors is speed adjustment and high torque characteristics.
The most common manufacturers of DC Motors are General Electric, Reliance Electric, and Baldor Electric. Westinghouse Electric, US/Emerson Electric, and Allis-Chalmers no longer produce DC Motors. European manufactures of DC Motors include: ABB, ASEA, Bull, Siemens, Brown Boveri, TT Electric, Thrige, and Leroy Summer. DC Motors have two sets of DC windings. The Field Windings are stationary and the Armature rotates. By applying different voltages to the different sets of windings, you can get different speeds and different performance characteristics. The armature voltage can be adjusted from full voltage all the way to zero. When you reduce the armature voltage, you decrease the speed and HP proportional with the reduction in voltage. Reducing the Field Voltage is called Field Weakening. By reducing the Field Voltage, the motor will speed up beyond its base speed (full voltage on the armature and fields). DC Fields are come in different configurations including Series, Shunt, Stabilized Shunt, and Compound.