Permanent Magnet DC Motor (PMDC)
A brushed DC motor type that produces the stator field with permanent magnets instead of a winding. Since the field is constant, speed varies almost linearly with the applied voltage and torque almost linearly with the armature current. It is the type most frequently met in automatic door, actuator and small crane applications.
Since there is no field current, its behaviour can be summarised with two constants: the EMF constant that gives the voltage produced per unit speed and the torque constant that gives the torque per ampere. That is why when you halve the average voltage with PWM the no-load speed also drops roughly by half; torque, on the other hand, is preserved as long as the current stays the same.
Practical consequences:
- Open-loop speed adjustment is predictable enough; in most applications an encoder is not needed.
- When the rotor stops the speed goes to zero, so the back-EMF goes to zero as well and the current is limited only by the winding resistance; the stall current rises very high.
- While decelerating, the motor behaves like a generator and pushes energy back into the supply line.
In 12 V and 24 V systems the same motor body can be produced with different windings; always verify the nominal voltage on the label. Running a 12 V motor on a 24 V supply by reducing the speed through the driver is not a safe method in terms of heat and brush life.
The context in which this term is used: DC Motor Driver Selection Guide