Why do permanent magnet motors demagnetize?

The core component in a permanent magnet motor is the permanent magnet, and high temperature is the biggest enemy of the permanent magnet.

Working at high temperatures for a long time will cause the permanent magnet motor to gradually lose magnetism, and the higher the temperature, the greater the risk of losing magnetism. When the temperature of the permanent magnet reaches a certain critical value, severe and irreversible demagnetization will occur. In addition, after the magnet is demagnetized, the current of the motor will increase, and the energy consumption will also increase.

This will increase the user’s electricity costs and may cause the motor to suddenly stop working, resulting in serious losses or danger. If the permanent magnet motor completely loses its magnetism, the motor must be completely replaced, which increases maintenance costs.

The reason for motor demagnetization:

①Incorrect magnet selection

Motors generally choose permanent magnets with high performance and high coercivity. For example, the N series of neodymium magnets can operate at a maximum temperature of 80°C; the H series can operate at 120°C; and the SH series can withstand high temperatures of 150°C. Depending on the motor’s operating temperature and magnetic field requirements, it is crucial to select high-quality and suitable magnets.

②The cooling fan is abnormal

The cooling fan of the motor is an important cooling system.Its function is to dissipate the heat inside the motor and keep the motor running at normal temperature. If there is an abnormality in the cooling fan, such as fan damage, poor heat dissipation, etc., it will cause the motor to be overheated, causing the motor to demagnetize.

③No temperature protection device is used

In order to protect the motor, many manufacturers will install a temperature protection device inside the motor. When the temperature is too high, the operating efficiency of the motor will be appropriately reduced and heat generation will be reduced. If the motor is not equipped with a temperature protection device, once the motor temperature is too high, it may cause failure or even cause the motor to burn out.

④Demagnetization caused by unreasonable motor design

Unreasonable design of the size and arrangement of the permanent magnets will lead to irreversible demagnetization of the motor. In addition, if the heat dissipation structure of the motor is not designed properly, it will also affect the heat dissipation effect of the motor, leading to demagnetization. In practical applications, these problems will cause the motor to fail to achieve its theoretical optimal performance.

How to prevent permanent magnet motor demagnetization?

permanent magnet motor

①Choose the appropriate power

Magnet demagnetization is related to the power of the motor. Selecting the appropriate power of a permanent magnet motor can prevent or delay demagnetization. The main reason for the demagnetization of the permanent magnet synchronous motor is excessive temperature, and overload is the main reason for excessive temperature. Therefore, in order to ensure the stable operation of the permanent magnet motor, we recommend that when selecting the motor power, a margin of about 20% needs to be left for the actual load conditions.

②Avoid overloading or frequent starts

AC asynchronous motors should try to avoid heavy load direct starting or frequent starting. During the asynchronous starting process, the starting torque oscillates. During the starting torque valley section, the stator magnetic field demagnetizes the rotor magnetic poles. Therefore, try to avoid overloading and frequent starting of asynchronous motors.

③Improve design

Because the design and manufacture of permanent magnet synchronous motors need to consider the relationship between armature reaction, electromagnetic torque and permanent magnet demagnetization. Properly increasing the thickness of the permanent magnets can effectively prevent demagnetization of the permanent magnets on the rotor surface. Because increasing the thickness of the permanent magnet can enhance the magnetic field strength inside the permanent magnet, making it less susceptible to the influence of the torque winding current and the magnetic flux generated by the radial force winding.

The ventilation slot loop can quickly dissipate the heat inside the rotor to prevent heat from accumulating inside the rotor, thus reducing the temperature of the rotor. Therefore, during structural design, designing the internal ventilation circuit of the rotor can reduce demagnetization.


Hope this article is helpful to you. We are a company specializing in the R&D, design and production of neodymium magnets.

If you want to know more about it or are interested in our products, please feel free to contact us.

Contact us:Contact | HQ Magnet (hq-magnet.com)

Learn more:Demagnetization – YouTube