If the temperature of the stepping motor is too high, the magnetic material of the motor will be demagnetized first, which will lead to the decrease of torque and even out of step. Therefore, the maximum temperature allowed for the appearance of the motor should depend on the demagnetization points of different magnetic materials of the motor. Generally speaking, the demagnetization points of the magnetic materials are all above 130 ℃, and some even as high as 200 ℃, So stepper motor surface temperature in 80-90 degrees centigrade completely normal.