What causes the stepper motor to be hot

As a digital actuator, stepper motor has been widely used in motion control system. When using the stepper motor, many users feel that the shell of the motor is hot when it works, and want to know why the stepper motor is hot. In fact, heating is a common phenomenon of stepper motors, but what degree of heating is normal, and how to minimize the heating of stepper motors?

First of all, it is necessary to understand why the stepper motor is hot. For all kinds of stepper motors, the interior is composed of iron cores and winding coils. The winding has resistance, and the power will produce loss, the loss is proportional to the square of the resistance and current, which is what we often say copper loss, if the current is not the standard DC or sine wave, it will also produce harmonic loss; The core has a hysteresis eddy current effect, which will also produce a loss in the alternating magnetic field, and its size is related to the material, current, frequency, and voltage, which is called iron loss. Copper loss and iron loss will be manifested in the form of heat, thus affecting the efficiency of the motor. The stepper motor generally pursues positioning accuracy and torque output, the efficiency is relatively low, the current is generally large, and the harmonic component is high, and the frequency of current alternating also changes with the speed, so the stepper motor is generally heated, and the situation is more serious than the general AC motor. Stepper motor at static and low speed, the current will remain relatively constant to maintain constant torque output. When the speed is high to a certain extent, the internal back potential of the motor increases, the current will gradually decrease, and the torque will also decrease. Therefore, the heat caused by copper damage is related to speed. Static and low speed heating is generally high, high speed heating is low. However, the change in iron loss (although the proportion is small) is not always the case, and the entire heat of the motor is the sum of the two. To sum up: what causes the stepper motor to be hot are these aspects:

1, the current set by the driver is larger than the rated current of the motor

2, the motor speed is too fast

3, the inertia and positioning torque of the motor itself is large, so even the medium-speed operation will heat up, but it does not affect the life of the motor. The demagnetization point of the motor is 130-200 ° C, so the motor is a normal phenomenon at 70-90 ° C, as long as it is less than 130 ° C, there is generally no problem, if you really feel overheating, set the current of the driver to about 70% of the rated current of the motor or the speed of the motor to reduce some.

So, how to control the heating of the stepper motor within a reasonable range? The degree to which the motor is allowed to heat mainly depends on the internal insulation level of the motor. The internal insulation properties will be destroyed at high temperatures (above 130 degrees). So as long as the interior does not exceed 130 degrees, the motor will not be damaged, and the surface temperature will be below 90 degrees. Therefore, the surface temperature of the stepper motor is normal at 70-80 degrees. Simple temperature measurement methods useful point thermometer, can also be roughly judged: with the hand can touch more than 1-2 seconds, not more than 60 degrees; With the hand can only touch, about 70-80 degrees; A few drops of water quickly vaporized, then more than 90 degrees; It can also be tested with a temperature gun.

Since this is the case, how to reduce the motor heat, that is, how to reduce copper loss and iron loss. There are two directions to reduce copper loss, reduce resistance and current, which requires that the motor with small resistance and small rated current should be selected as far as possible in the selection of two-phase motors, which can be connected in series without parallel motors. However, this often contradicts the requirements of torque and high speed. For the motor that has been selected, it should make full use of the driver's automatic half-current control function and off-line function, the former automatically reduces the current when the motor is at static, the latter simply cuts off the current. In addition, because the current waveform of the subdivision driver is close to sine, the harmonics are less, and the motor will heat less. There are not many ways to reduce 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 bring the increase of heat. Therefore, the appropriate driving voltage level should be selected, taking into account high-speed, stationary and heat, noise and other indicators.

We will consider whether the heating phenomenon has any effect on the motor? Although the motor heating generally does not affect the life of the motor, for most customers there is no need to pay attention. However, a severe fever can have some negative effects. If the thermal expansion coefficient of each part of the motor is different, the change of structural stress and the small change of the internal air gap will affect the dynamic response of the motor, and the high speed will be easy to lose step. For example, some occasions do not allow excessive heat of the motor, such as medical devices and high-precision test equipment. Therefore, the heating of the motor should be controlled as necessary.