Problem solving

Stepper motor heating problem
Release Date : 2019-03-08 09:27:30

First, the reason for the stepper motor heating:

Why is the stepper motor hot? For various stepper motors, the inside is composed of a core and a winding coil. The winding has resistance, and the power will generate loss. The magnitude of the loss is proportional to the square of the resistance and current. This is what we often call copper . If the current is not a standard DC or sine wave, harmonic loss will occur. The eddy current effect, in the alternating magnetic field, also produces losses, the size of which is related to material, current, frequency, voltage, which is called iron loss. Both copper loss and iron loss are manifested in the form of heat, which affects the efficiency of the motor.

Stepper motors generally pursue positioning accuracy and torque output, the efficiency is relatively low, the current is generally large, and the harmonic components are high. The frequency of the alternating current also varies with the rotational speed. Therefore, the stepping motor generally has a fever condition, and the situation is more general. A reasonable range of AC motors, a reasonable range of stepper motor heating, to what extent the motor heat is allowed, mainly depends on the internal insulation level of the motor. The internal insulation properties are destroyed 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. Therefore, the stepper motor surface temperature is normal at 70-80 degrees. The simple temperature measurement method can be used as a point thermometer, or it can be roughly judged: It can be touched by hand for 1-2 seconds or more, no more than 60 degrees; it can only be touched by hand, about 70-80 degrees; If it is more than 90 degrees, when the stepper motor heats up with the speed, the constant current driving technology is adopted. When the stepping motor is static and low speed, the current will remain relatively constant to maintain the constant torque output. When the speed is high to a certain extent, the internal back EMF of the motor rises, the current will gradually decrease, and the torque will also decrease. Therefore, the heat generated by the copper loss is related to the speed. Generally, the heat is high at static and low speeds, and low at high speeds. However, the change in iron loss (although the proportion is small) is not always the case, and the whole heat of the motor is the sum of the two, so the above is only the general case.

Second, the harmfulness of the motor's heating phenomenon:

The effect of heat on the motor Although it does not generally affect the life of the motor, it is not necessary for most customers. However, severe fever can have some negative effects. If the thermal expansion coefficient of each part of the motor is different, the structural stress changes and the small change of the internal air gap will affect the dynamic response of the motor, and the high speed will easily lose the step. In some cases, excessive heating of the motor, such as medical equipment and high-precision test equipment, is not allowed.

Third, the solution to the heating problem of stepper motor:

1. Reduce the heat generated by the motor to reduce heat, which is to reduce copper loss and iron loss. There are two directions to reduce copper loss, which reduces the electric current and current. This requires that the motor with small resistance and small rated current should be selected in the selection. For two-phase motors, the parallel motor can be used with the series motor, but this often It is in conflict with the requirements of torque and high speed. 

2. For the motor that has been selected, the automatic semi-flow control function and offline function of the drive should be fully utilized. The former automatically reduces the current when the motor is static, and the latter simply cuts off the current.

3. In addition, the subdivision driver has less harmonics due to the current waveform, and the motor has less heat. There are not many ways to reduce iron loss, and the voltage level is related to it. Although the high-voltage drive motor will bring about the improvement of high-speed characteristics, it also brings about an increase in heat.

4, should choose the appropriate drive voltage level, taking into account high band, stability and heat, noise and other indicators.