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Stepper motor heating and its effects

1. The main reasons for motor heating:
The types of motors we usually see have iron cores and winding coils inside. The winding has resistance, and the loss will be generated when the current is applied. The loss is proportional to the square of the resistance and the current. This is what we often call copper loss. If the current is not a standard DC or sine wave, it will also generate harmonic losses; the core has hysteresis. The eddy current effect also generates losses in the alternating magnetic field. Its size is related to the material, current, frequency, and voltage. This is called iron loss. Both copper and iron losses are manifested as heat, which affects the efficiency of the motor. Stepping motors generally pursue positioning accuracy and torque output. They have low efficiency, high currents, high harmonic components, and high-frequency currents. The frequency of the alternating current also changes with the rotation speed. AC motor is severe.

2. Reasonable range of stepper motor heating:
The degree to which the motor heat is allowed depends mainly on the internal insulation level of the motor. The internal insulation performance will be destroyed at high temperature (above 130 degrees). So as long as the interior does not exceed 130 degrees, the motor will not damage the ring, and the surface temperature will be below 90 degrees. Therefore, the surface temperature of the stepping motor is normal at 70-80 degrees. The simple temperature measurement method is with a thermometer, and you can also make a rough judgment: 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 hands, about 70-80 degrees; It will be over 90 degrees.

3. The change of heating of stepping motor with speed:
When using constant current drive technology, the stepper motor maintains a constant current under static and low speed to maintain constant torque output. If the speed is high, the back-EMF inside the motor will increase, the current will gradually decrease, and the torque will also decrease. Therefore, the heat generation caused by copper loss is related to speed. Fever is generally high at static and low speeds, and low at high speeds. However, the change of iron loss (although the proportion is relatively small) is not entirely the same, and the entire heat of the motor is the sum of the two, so the above is only a general situation.

4, the impact of fever:
Although the motor heat generally does not affect the life of the motor, it is not necessary for most customers to pay attention to it. But in severe cases, it will bring some negative effects. For example, the different thermal expansion coefficients of the various parts of the motor will cause changes in structural stress and small changes in the internal air gap, which will affect the dynamic response of the motor, and it will be easy to lose steps at high speeds. Another example is that excessive heating of the motor is not allowed in some occasions, such as medical equipment and high-precision test equipment. Therefore, it is necessary to control the heating of the motor.

5. How to reduce the heat of the motor:
To reduce heat is to reduce copper and iron losses. There are two directions for reducing copper loss, reducing resistance and current. This requires that motors with low resistance and low rated current should be selected as much as possible in the selection. For two-phase motors, series motors can be used instead of parallel motors. But this often conflicts with the requirements of torque and high speed. For the selected motor, the driver's automatic half-current control function and offline function should be fully utilized. The former automatically reduces the current when the motor is at a standstill, and the latter simply cuts off the current. In addition, since the current waveform of the subdivided driver is close to the sine, there will be less harmonics, and the motor will generate less heat. There are not many ways to reduce the iron loss, and the voltage level is related to it. Although the high-voltage driven motor will bring the improvement of high-speed characteristics, it will also increase the heat generation. Therefore, an appropriate driving voltage level should be selected, taking into account high-speed, smoothness, heat, noise and other indicators.
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