When a stepper motor starts, it generates an operating current to suppress rolling, similar to an elevator suspended in mid-air. This current causes the motor to heat up, which is normal.
1. Reason 1
One of the most significant advantages of stepper motors is their ability to achieve precise control within an open-loop system. Open-loop control means that no feedback information regarding the (rotor) position is required. This control avoids the use of expensive sensors and feedback devices like optical encoders, as the (rotor's) position can be determined simply by tracking the input stepper pulses. Recently, some customers have reported to our engineers at Shanshe Motors that stepper motors tend to overheat. So, how should this situation be handled?
1. Reduce stepper motor heat generation, which means reducing copper and iron losses. Reducing copper losses has two aspects: reducing resistance and current. This requires selecting motors with low resistance and low rated current when choosing a model. For two-phase stepper motors, use series motors instead of parallel motors if possible, but this often conflicts with torque and high-speed requirements.
2. For the selected motor, the active half-current control function and offline function of the driver should be fully utilized. The former actively reduces the current when the motor is in a static state, and the latter simply cuts off the current.
3. Additionally, microstepping motor drivers have a current waveform close to a sine wave, resulting in fewer harmonics and less motor heat generation. There are few ways to reduce iron losses; voltage level is relevant. While high-voltage drives improve high-speed performance, they also increase heat generation.
4. A suitable voltage level for the drive motor should be selected, taking into account factors such as high performance, stability, heat generation, and noise.
2. Reason Two
While stepper motor overheating generally doesn't affect its lifespan and is usually not a concern for most customers, it can have negative consequences in severe cases. For example, differences in the thermal expansion coefficients of different parts within the stepper motor can alter structural stress and even subtle changes in the internal air gap, affecting the motor's dynamic response and potentially causing step loss at high speeds. Furthermore, excessive stepper motor heat is unacceptable in certain applications, such as medical devices and high-precision testing equipment. Therefore, it's essential to control stepper motor overheating. The causes of stepper motor overheating include the following:
1. The current set for the driver is greater than the rated current of the motor.
2. The motor speed is too fast.
3. The motor itself has a large inertia and positioning torque, so it will generate heat even when running at medium speed, but this will not affect the motor's lifespan. The demagnetization point of the motor is between 130-200℃, so a motor temperature of 70-90℃ is normal. As long as it is below 130℃, there is generally no problem. If you really feel that it is overheating, set the driver current to about 70% of the motor's rated current or reduce the motor speed.
3. Reason Three
Stepper motors, as digital actuators, are now widely used in motion control systems. Many users notice that stepper motors get quite hot during operation and are concerned about whether this is normal. In fact, heat generation is a common phenomenon with stepper motors, but what level of heat is considered normal, and how can we minimize stepper motor heat generation?
Below, we will provide a brief breakdown, hoping to find practical applications in actual work:
1. The principle of motor heating
Most motors we see contain an iron core and winding coils. The windings have resistance, and losses occur when current flows through them. The magnitude of these losses is proportional to the resistance and the square of the current; this is what we commonly call copper loss. If the current is not standard DC or a sine wave, harmonic losses will also occur. The iron core has hysteresis and eddy current effects, which also cause losses in an alternating magnetic field. The magnitude of these losses depends on the material, current, frequency, and voltage; this is called iron loss. Both copper and iron losses manifest as heat, thus affecting the motor's power. Stepper motors generally prioritize positioning accuracy and torque output, resulting in relatively low power consumption, generally high current, and high harmonic content. The frequency of the alternating current also changes with the rotational speed. Therefore, stepper motors commonly experience heat generation, and this is more severe than with typical AC motors.
2. Reasonable range of stepper motor heating
The acceptable temperature level for a motor depends primarily on its internal insulation class. Internal insulation only deteriorates at high temperatures (above 130 degrees Celsius). Therefore, as long as the internal temperature doesn't exceed 130 degrees Celsius, the motor won't be damaged, and the surface temperature will be below 90 degrees Celsius. Thus, a surface temperature of 70-80 degrees Celsius is normal for a stepper motor. A simple temperature measurement method using a spot thermometer can also provide a rough estimate: if you can touch it with your hand for more than 1-2 seconds, it's below 60 degrees Celsius; if you can only touch it briefly, it's approximately 70-80 degrees Celsius; if a few drops of water vaporize quickly, it's above 90 degrees Celsius.
3. The change in stepper motor heat generation with speed
When using constant current drive technology, the stepper motor maintains a constant current at static and low speeds to ensure constant torque output. As the speed increases, the internal back electromotive force rises, the current gradually decreases, and the torque also decreases. Therefore, the heat generated by copper losses is speed-dependent. Generally, heat generation is high at static and low speeds and low at high speeds. However, the change in iron losses (although they account for a smaller proportion) is not always consistent, and the total heat generation of the motor is the sum of both losses and iron losses; therefore, the above is only a general observation.
4. Effects of fever
While motor overheating generally doesn't affect its lifespan and is usually not a concern for most customers, it can have negative consequences in severe cases. For example, differences in the thermal expansion coefficients of different parts of the motor can alter structural stress and cause subtle changes in internal air gaps, affecting the motor's dynamic response and potentially leading to loss of synchronization at high speeds. Furthermore, excessive motor overheating is unacceptable in certain applications, such as medical devices and high-precision testing equipment. Therefore, it is essential to control motor overheating.
5. How to reduce motor heat generation
Reducing heat generation essentially means reducing copper and iron losses. Reducing copper losses has two aspects: reducing resistance and current. This requires selecting motors with low resistance and low rated current during the selection process. For two-phase motors, series connection should be used whenever possible instead of parallel connection. However, this often conflicts with torque and high-speed requirements. For motors already selected, the active half-current control and offline functions of the driver should be fully utilized. The former actively reduces current when the motor is static, while the latter completely cuts off the current. Additionally, microstepping drivers, because their current waveform is close to a sine wave with fewer harmonics, also generate less heat. There are fewer methods to reduce iron losses, and voltage level is relevant. While high-voltage drives improve high-speed performance, they also increase heat generation. Therefore, an appropriate drive voltage level should be selected, balancing high speed, stability, heat generation, and noise levels.
All stepper motors consist internally of an iron core and winding coils. The windings have resistance, and losses occur when current flows through them. The magnitude of these losses is proportional to the resistance and the square of the current; this is what we commonly call copper losses. If the current is not standard DC or a sine wave, harmonic losses will also occur. The iron core has hysteresis and eddy current effects, which also cause losses in an alternating magnetic field. The magnitude of these losses depends on the material, current, frequency, and voltage; this is called iron loss. Both copper and iron losses manifest as heat, thus affecting the motor's power. Stepper motors generally prioritize positioning accuracy and torque output, resulting in relatively low power consumption, generally high current, and high harmonic content. The frequency of the alternating current also changes with the rotational speed. Therefore, stepper motors commonly experience heat generation, and this is more severe than with typical AC motors.
