Exploring the impact of temperature on motor performance (I)

First, we need to focus on the various materials in the motor and examine them in the following order:

1. Insulation material: ensure the highest temperature it can withstand.

2. Magnet: Make sure it can withstand the highest temperature and pay attention to the effect of temperature on magnetism.

3. Enameled wire: Ensure the highest temperature it can withstand and pay attention to the change of resistance due to temperature.

4. Bearings: Ensure the operating temperature range of the lubricating oil.

5. Export power cord: ensure the highest temperature it can withstand.

Among them, the heat resistance of insulating materials, enameled wires, and export power cords directly affects safety. If the heat resistance level of these materials is insufficient, it may cause the motor to burn out or even cause a fire. In addition, the heat resistance of magnets, enameled wires, and bearings will also indirectly affect the performance of the motor because they will cause additional energy loss, which in turn increases the temperature of the motor.

A motor is a device that converts electrical energy into kinetic energy. During the energy transfer and conversion process, some energy will be lost, which will be converted into heat energy, causing the motor temperature to rise. If the temperature exceeds the upper limit of the material's heat resistance, it may cause damage to the material.

Therefore, an excellent motor design needs to take into account the energy loss of the motor and carry out proper heat dissipation planning to ensure that the temperature inside the motor can be maintained at a stable state and is lower than the upper limit of the heat resistance of the materials and parts. Common upper limits of heat resistance inside motors are 150 degrees, 120 degrees, 80 degrees, and 60 degrees.

In addition to the direct impact of the upper limit of heat resistance on safety, the temperature characteristics of the two materials, enameled wire and magnet, will also affect the performance of the motor. For example, the magnetic force of the magnet will decrease as the temperature increases. Since the motor generates torque through the interaction of electricity and magnetic force, when the magnetic force decreases, the torque will also decrease, or more electricity will be required to compensate to meet the torque demand.

When a magnet is affected by temperature, its magnetic strength will change, which means that the characteristics of the motor will change due to temperature changes. As shown in the figure below, the characteristic curve of this permanent magnet motor is not a single oblique straight line as we described earlier, but more like a broken line. After further analysis, we can find that this is actually a combination of two oblique straight lines, where the blue dotted line represents the characteristics before the temperature change, and the red dotted line represents the result after the temperature change. From this we can see that the characteristics of the motor before and after the temperature rise may be very different. From the example in the figure below, the maximum torque value may have a difference of nearly three times, which shows that the magnet is quite sensitive to temperature.

In addition to affecting the torque output of the motor, temperature also affects the efficiency of the motor. The main reason is that the resistance of copper increases with the increase of temperature, as shown in the figure below, which will lead to an increase in the copper loss of the motor.

From the motor efficiency characteristic curve in the figure below, we can see that the blue curve represents the efficiency before the temperature rises, while the red curve represents the efficiency after the temperature rises. We can see that the temperature change of copper loss does have a certain impact on the efficiency, but the maximum difference is only about 5%, which is not as drastic as the reaction of the magnet. The main reason is that although the resistance of copper is affected by temperature, its change range is not as large as that of the magnet, so the impact is relatively small.

Key points:

The effect of temperature on motor output characteristics is extremely significant.

Magnets play a key role in this process.