DC Motors
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
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