Industrial applications use dc motors because the speed-torque relationship can be varied to almost any useful form -- for both dc motor and regeneration applications in either direction of rotation. Continuous operation of dc motors is commonly available over a speed range of 8:1. Infinite range (smooth control down to zero speed) for short durations or reduced load is also common.
Dc motors are often applied where they momentarily deliver three or more times their rated torque. In emergency situations, dc motors can supply over five times rated torque without stalling (power supply permitting).
Dynamic braking (dc motor-generated energy is fed to a resistor grid) or regenerative braking (dc motor-generated energy is fed back into the dc motor supply) can be obtained with dc motors on applications requiring quick stops, thus eliminating the need for, or reducing the size of, a mechanical brake.
Dc motors feature a speed, which can be controlled smoothly down to zero, immediately followed by acceleration in the opposite direction -- without power circuit switching. And dc motors respond quickly to changes in control signals due to the dc motor's high ratio of torque to inertia.
DC Motor types: Wound-field dc motors are usually classified by shunt-wound, series-wound, and compound-wound. In addition to these, permanent-magnet and brushless dc motors are also available, normally as fractional-horsepower dc motors. Dc motors may be further classified for intermittent or continuous duty. Continuous-duty dc motors can run without an off period.
DC Motors - Speed control: There are two ways to adjust the speed of a wound-field dc motor. Combinations of the two are sometimes used to adjust the speed of a dc motor.
DC Motors: DC Motor Types