basic training industrial duty and commercial duty electric motors gear reducers pdf

The development of power semiconductors and microprocessors has brought efficient adjustable speed control to AC motors through the use of inverter drives. Through this technology, the most recent designs of so-called pulse width modulated AC drives are capable of speed and
torque regulation that equals or closely approximates direct current systems.

Marathon Motors also produces permanent-magnet direct current motors. The DC motor is the oldest member of the electric motor family. Technological breakthroughs in magnetic materials, as well as solid state electronic controls and high-power-density rechargeable batteries, have all revitalized the versatile DC motor.

DC motors have extremely high torque capabilities and can be used in conjunction with relatively simple solid state control devices to give programmed acceleration and deceleration over a wide range of selected speeds. Because the speed of a DC motor is not dependent on the number of poles, there is great versatility for any constant or variable speed requirement.

In most common DC motors, the magnetic field is produced by highstrength permanent magnets, which have replaced traditional field coil windings. The magnets require no current from the power supply. This improves motor efficiency and reduces internal heating. In addition, the reduced current draw enhances the life of batteries used as power supplies in mobile or remote applications.