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Over-Heating Of Stepper Motor

Over-Heating Of Stepper Motor

1. Is it a normal phenomenon? what is the general temperature range of motor heat? here'ss the motor heat principle :

All kinds of motors we usually see are core and winding coils inside. Winding has resistance, when power on it will have power losses, this is we called copper loss. if the current is not standard DC or sine wave,it will produce harmonic loss; the iron core has hysteresis eddy current effect, in the alternating magnetic field will also have a loss, it affects by its size, material,current, voltage and frequency, this is called iron loss. Both copper and iron loss will be shown in the form of heat, which affects the efficiency of the motor. 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. The alternating frequency of the current changes with the speed. Therefore, the stepper motor generally has heating situation, and the situation is more serious than the general AC motor.

2. The reasonable range of the step motor heating:

The degree of the motor allowed to heat is mainly dependent on the internal insulation level of the motor. The internal insulation performance will be destroyed at high temperature (more than 130 degrees). So if the internal temperature does not exceed 130 degrees, the motor will not damage, and the surface temperature will below 90 degrees. Therefore, the surface temperature of the stepping motor is normally at 70 to 80 degrees. A simple temperature measurement method is to use point thermometer. Or also can be roughly estimated by this: If can touch by hand for more than 1 or 2 seconds,means it will not exceed 60 degrees; only can be touched by hand for 1 time, its about 70 to 80 degrees; drops of water rapidly vaporize, and it is above 90 degrees.  

3.Stepper motor's heat change with the speed

With constant current drive, the stepper motor will maintain constant current at static and low speed to maintain constant torque output. When the speed rise to a certain value, the back EMF inside the motor rises, the current will decline gradually and the torque will also decrease. Therefore, the heat caused by the copper loss is related to the speed. In static and low speed, the general heat is high;in high speed,the heat is low. But the iron loss (although a small proportion) is not the same. And the whole heat of the motor is the sum of the two, so the above is only the general situation.

4. The effect of motor heat:

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 it will bring some negative effects when it is serious. If the thermal expansion coefficient of each part of the motor is different, the change of the structural stress and the tiny change of the internal air gap will affect the dynamic response of the motor, when in high speed it will easily lose step. In some cases, not allow excessive heat of the motor, such as medical equipment and high precision testing equipment. Therefore, the heat of the motor should be controlled.

5. How to reduce the heat of the motor:

Reducing heat is to reduce copper loss and iron loss. There are two ways to reduce copper loss-reduce resistance and current. This requires to choose a motor with small resistance and a small rated current. For a two phase motor, it can use connecting ways by series instead of parallel. But this is often inconsistent with the torque and high speed requirements. For the selected motor, we should make full use of the automatic half flow control function and offline function of the driver. The former automatically reduces the current when the motor is at a static state, and the latter simply cuts off the current. In addition, the current waveform is close to sine for the subdivision drives ,so it will have less harmonics and less heat. There are not many ways to reduce the loss of iron. The voltage level is related to it. The motor driven by high voltage will bring about high speed characteristics, but it also brings about the increase of heat. Therefore, the appropriate driving voltage level should be selected and also should consider high speed performance, smoothness, heat and noise.