Definition: Detent Torque is defined as the torque at the maximum load that is applied to the shaft of the motor which is unexcited without causing continuous rotation. It is also known as Restraining Torque and is produced in the rotor of the permanent magnet motor.
The detent torque exists because of the residual magnetism in the permanent magnetic material used for the construction of the rotor of the motor. It is produced when the stator coils are not energized. This torque prevents the rotor from drifting when the motor supply is turned off.
The torque which is caused by the motor when the rated current flow across the winding is known as the holding torque. Detent torque is beneficial for stopping the motor. It also resists the momentum of the moving rotor and the friction in the rotating components. Such type of torque ranges from 5 to 20% of the holding torque.
When the motor is unexcited, the permanent magnet and hybrid stepper motor develop a detent torque confining the rotation of the rotor.