For various stepper motors, the inside of the stepper motor is composed of an iron core and a winding coil. The winding has resistance, and power will cause loss. The loss is proportional to the resistance and the square of the current. This is what we often call copper loss. If the current is not a standard DC or sine wave, harmonic loss will also be generated, the iron core has a hysteresis eddy current effect, and it will also cause loss in the alternating magnetic field. Its size is related to the material, current, frequency, and voltage. This is called iron loss. Copper loss and iron loss will both appear in the form of heat, thereby affecting the efficiency of the motor. Stepper motors generally pursue positioning accuracy and torque output, with relatively low efficiency. The current is generally large, and the harmonic component is high. The frequency of current alternation also changes with the speed. Therefore, stepper motors generally have heating conditions, and the situation is more serious than that of general AC motors.
To what extent is the motor heating allowed?
The normal degree of motor heating mainly depends on the internal insulation level of the motor. The internal insulation performance will be destroyed only at high temperatures (above 130 degrees). Therefore, as long as the internal temperature does not exceed 130 degrees, the motor will not be damaged, and the surface temperature will be below 90 degrees at this time. Therefore, the surface temperature of the stepper motor is normal at 70-80 degrees. A simple temperature measurement method is to use a thermometer, which can also be roughly judged: you can touch it with your hand for more than 1-2 seconds, not more than 60 degrees, you can only touch it with your hand, about 70-80 degrees, a few drops of water quickly vaporize, then it is above 90 degrees, of course, you can also use a temperature gun to detect.
Some medical devices and high-precision test equipment require strict control of mechanical heating, so how to control the heating of stepper motors?
Reducing heating means reducing copper loss and iron loss. There are two directions to reduce copper loss, reducing resistance and current. This requires that when selecting a motor, try to choose a motor with small resistance and small rated current. For two-phase motors, you can use a series motor instead of a parallel motor. But this often conflicts with the requirements of torque and high speed. For the motor that has been selected, you should make full use of the automatic half-current control function and offline function of the driver. The former automatically reduces the current when the stepper motor is in a static state, and the latter simply cuts off the current. In addition, since the current waveform of the subdivision driver is close to sine wave and has few harmonics, the stepper motor will also generate less heat. There are not many ways to reduce iron loss, and the voltage level is related to it. Although the high-voltage driven stepper motor will improve the high-speed characteristics, it will also increase the heat. Therefore, the appropriate stepper motor drive voltage level should be selected, taking into account the high-speed, stability, heat, noise and other indicators.