About the heating of the stepper motor

Is the stepper motor heating normal? What is the general temperature range?

1, the principle of motor heating:

The various types of motors we usually see have iron cores and winding coils inside. The winding has resistance, and the power will generate loss. The loss is proportional to the square of the resistance and current. This is the copper loss we often say. If the current is not a standard DC or sine wave, harmonic loss will occur. The core has hysteresis. The eddy current effect also causes loss in the alternating magnetic field, and its magnitude is related to material, current, frequency, and voltage. This 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, and 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. The AC motor is serious.

2, the reasonable range of stepper motor heating:

The extent to which the motor is allowed to heat up depends mainly on the internal insulation rating of the motor. Internal insulation properties are destroyed at high temperatures (above 130 degrees). Therefore, as long as the internal does not exceed 130 degrees, the motor will not damage the ring, 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 is useful for point thermometers. It can also be roughly judged: it can be touched by hand for more than 1-2 seconds, not more than 60 degrees; it can only be touched by hand, about 70-80 degrees; a few drops of water quickly It is 90 degrees or more.

3, stepper motor heating with speed changes:

With constant current drive technology, the stepper motor maintains a constant current at both static and low speeds to maintain 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 a general case.

4, the impact of fever:

Although the motor heat does not generally affect the life of the motor, it is not necessary for most customers. But when it is serious, it will bring 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. Therefore, the necessary control of the heating of the motor should be carried out.

5. How to reduce the heating of the motor:

Reducing heat is reducing copper loss and iron loss. Reducing the copper loss has two directions, reducing the resistance and current. This requires that the motor with small resistance and small rated current be selected as much as possible during the selection. For the two-phase motor, the parallel motor can be used for the series motor. But this often contradicts the requirements of torque and high speed. For the selected motor, the driver's automatic semi-flow control function and offline function should be fully utilized. The former automatically reduces the current when the motor is static, and the latter simply cuts off the current. In addition, because the current waveform is close to sinusoidal, the subdivision driver has less harmonics and less motor heating. 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. Therefore, we should choose the appropriate driving voltage level, taking into account the high speed, smoothness and heat, noise and other indicators.

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Label: About the heating of the stepper motor

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