How does temperature affect the performance of BLDC motor magnets?

Temperature is a critical factor that significantly influences the performance of BLDC (Brushless Direct Current) motor magnets. As a supplier of BLDC Motor Magnet, I have witnessed firsthand how temperature variations can impact the functionality and efficiency of these magnets. In this blog, we will delve into the science behind the temperature effects on BLDC motor magnets and explore the implications for motor performance.

Basic Principles of BLDC Motor Magnets

Before discussing the temperature effects, it is essential to understand the basic principles of BLDC motor magnets. BLDC motors use permanent magnets to generate a magnetic field, which interacts with the stator's electromagnetic field to produce torque and rotation. The most commonly used magnets in BLDC motors are neodymium-iron-boron (NdFeB) and samarium-cobalt (SmCo) magnets, known for their high magnetic strength and energy density.

The performance of these magnets is characterized by several key parameters, including remanence (Br), coercivity (Hc), and maximum energy product ((BH)max). Remanence refers to the magnetic flux density remaining in the magnet after it has been magnetized. Coercivity is the measure of the magnet's resistance to demagnetization. The maximum energy product represents the maximum amount of magnetic energy that can be stored in the magnet.

Temperature Effects on Magnetic Properties

1. Remanence (Br)

Temperature has a significant impact on the remanence of BLDC motor magnets. As the temperature increases, the thermal energy causes the magnetic moments within the magnet to become more disordered, leading to a decrease in the overall magnetic flux density. This phenomenon is known as the reversible temperature coefficient of remanence (αBr).

For NdFeB magnets, the remanence typically decreases linearly with increasing temperature. The αBr value for NdFeB magnets is relatively high, usually in the range of -0.12%/°C to -0.13%/°C. This means that for every 1°C increase in temperature, the remanence of the magnet decreases by approximately 0.12% to 0.13%.

On the other hand, SmCo magnets have a much lower αBr value, typically around -0.03%/°C to -0.04%/°C. This makes SmCo magnets more stable at high temperatures compared to NdFeB magnets.

2. Coercivity (Hc)

Coercivity is another critical magnetic property that is affected by temperature. As the temperature rises, the magnetic domain walls within the magnet become more mobile, making it easier for the magnet to be demagnetized. This results in a decrease in coercivity, which is known as the reversible temperature coefficient of coercivity (αHc).

NdFeB magnets have a relatively high αHc value, typically in the range of -0.6%/°C to -0.7%/°C. This means that for every 1°C increase in temperature, the coercivity of the magnet decreases by approximately 0.6% to 0.7%.

SmCo magnets, on the other hand, have a much lower αHc value, usually around -0.3%/°C to -0.4%/°C. This makes SmCo magnets more resistant to demagnetization at high temperatures.

3. Maximum Energy Product ((BH)max)

The maximum energy product is a measure of the magnet's ability to store magnetic energy. Since both remanence and coercivity are affected by temperature, the maximum energy product also decreases with increasing temperature.

The decrease in (BH)max is more pronounced for NdFeB magnets compared to SmCo magnets due to their higher temperature coefficients of remanence and coercivity.

Irreversible Demagnetization

In addition to the reversible temperature effects on magnetic properties, high temperatures can also cause irreversible demagnetization of BLDC motor magnets. Irreversible demagnetization occurs when the temperature exceeds a certain critical value, known as the Curie temperature (Tc).

The Curie temperature is the temperature at which the magnetic material loses its ferromagnetic properties and becomes paramagnetic. For NdFeB magnets, the Curie temperature is typically around 310°C to 400°C, while for SmCo magnets, it is around 700°C to 800°C.

When the temperature exceeds the Curie temperature, the magnetic moments within the magnet become completely disordered, and the magnet loses its magnetization. Once irreversible demagnetization occurs, the magnet cannot regain its original magnetic properties even if the temperature is lowered.

Implications for BLDC Motor Performance

The temperature effects on BLDC motor magnets have several implications for motor performance.

1. Torque and Power Output

Since the remanence and maximum energy product of the magnets decrease with increasing temperature, the torque and power output of the BLDC motor also decrease. This can lead to a reduction in the motor's efficiency and performance, especially at high temperatures.

2. Speed and Control

The decrease in coercivity at high temperatures can make the motor more susceptible to demagnetization, which can affect the motor's speed and control. Demagnetization can cause the motor to lose synchronism with the stator's electromagnetic field, leading to erratic operation and reduced performance.

3. Reliability and Lifespan

Irreversible demagnetization can significantly reduce the reliability and lifespan of the BLDC motor. Once the magnets are demagnetized, the motor may no longer function properly, and the magnets may need to be replaced.

Mitigating Temperature Effects

To mitigate the temperature effects on BLDC motor magnets, several strategies can be employed.

1. Magnet Selection

Choosing the right type of magnet for the specific application is crucial. If the motor is expected to operate at high temperatures, SmCo magnets may be a better choice due to their lower temperature coefficients and higher Curie temperatures.

2. Thermal Management

Effective thermal management is essential to keep the temperature of the motor and magnets within acceptable limits. This can include using heat sinks, fans, or liquid cooling systems to dissipate heat from the motor.

3. Design Optimization

Optimizing the motor design can also help to reduce the temperature effects on the magnets. This can include using larger magnets, improving the magnetic circuit design, or reducing the current density in the motor.

Conclusion

Temperature is a critical factor that significantly affects the performance of BLDC motor magnets. As a BLDC Motor Magnet supplier, we understand the importance of providing high-quality magnets that can withstand the temperature challenges of different applications.

By understanding the temperature effects on magnetic properties and implementing appropriate mitigation strategies, we can ensure that BLDC motors operate efficiently and reliably over a wide range of temperatures.

If you are in the market for high-quality BLDC motor magnets or need more information about our products, please feel free to contact us for a procurement discussion. We are committed to providing you with the best solutions for your motor applications.

References

• Handbook of Magnetic Materials, edited by K. H. J. Buschow
• Magnetic Materials and Their Applications, by E. C. Stoner and E. P. Wohlfarth
• Brushless Permanent-Magnet and Reluctance Motor Drives, by T. J. E. Miller