Permanent magnet DC (PMDC) Motors use a strong, permanent magnets to produce the motor’s magnetic field. Due to this constant magnetic field, PMDC motors are characterized by a consistent speed-torque response over the motor’s operating range (up to base speed).
They are more compact and efficient with better thermal characteristics than wound-field DC motors so they can be used for continuous duty applications. But they have lower horsepower ratings than wound-fields; therefore, they are used in functions such as the steering (motor-pump) system and some lifting pump drive applications.
In addition, PMDC motors have a lower stall torque than wound-field DC motors. Wound-field DC motors use electromagnetic excitation to produce the motor’s magnetic field. When used in a series-field configuration, they have very high starting torque. They have high horsepower ratings so they can be used for high load applications at much higher speeds than PMDC motors.
Typically, they will be used to power the traction drive, steering systems or the lifting system’s hydraulic pump drive. Their thermal characteristics make them most suitable for intermittent duty applications. DC motor control in electric forklifts is usually a voltage control, chopper system (DC-to-DC converter) using a buck/boost chopper circuit.
