Advantages of Permanent Magnet DC Motor or PMDC Motor
PMDC motor have some advantages over other types of DC motors. They are :
- No need of field excitation arrangement.
- No input power in consumed for excitation which improve efficiency of DC motor.
- No field coil hence space for field coil is saved which reduces the overall size of the motor.
- Cheaper and economical for fractional kW rated applications.
Disadvantages of Permanent Magnet DC Motor or PMDC Motor
- In this case, the armature reaction of DC motor cannot be compensated hence the magnetic strength of the field may get weak due to demagnetizing effect armature reaction.
- There is also a chance of getting the poles permanently demagnetized (partial) due to excessive armature current during starting, reversal and overloading condition of the motor.
- Another major disadvantage of PMDC motor is that, the field in the air gap is fixed and limited and it cannot be controlled externally. Therefore, very efficient speed control of DC motor in this type of motor is difficult.
DC spur gear motor including a dc motor and a spur gearbox.
A spur gearbox could be either square type or round type as following:
According to the size of the gearbox, normally we have 12mm dc spur gear motor, 25mm dc spur gear motor, and 37mm dc spur gear motor and so on.
DC Spur Gear Motor are relative simple in production, so the output efficiency is limited. According to the stages of the gear trains, the efficiency reduce one by one. However, the price would be a bit cheaper than other types dc gear motor.