Comparison of permanent magnet brushless motors with inner and outer rotors for large industrial ceiling fans

Permanent magnet brushless motors have the advantages of small size, low noise, and maintenance-free, and are widely used by many large industrial ceiling fan manufacturers. In recent years, the development prospects of permanent magnet motors are very good, and permanent magnet brushless fans also meet customer needs. Permanent magnets are divided into an inner rotor and an outer rotor, which has led to the emergence of an inner rotor permanent magnet brushless motor fan. However, there is no option for an outer rotor motor. What are the differences between the two? Let's take a closer look.

Firstly, the two differ in the material installation: the Duntex iron magnetic material of the inner rotor motor is embedded, which is fixed by the structure and will not have the phenomenon of adhesive aging and failure like the outer rotor. The Qintie clock broken material will not fall off. The Duntex iron magnetic material of the outer rotor motor is adhesive, and if the adhesive ages and fails, then the Qintie clock broken material will fall off, causing the stator and rotor of the motor to jam and the motor to become scrapped, which will cause significant losses to users. This is also why the warranty period of inner rotor motors is longer than that of outer rotor motors on the market.

Secondly, the two differ in motor performance: the inner rotor adopts a polyphase structure, and the air gap magnetic field is between 1.0-1.4T, greatly improving the magnetic field strength. Therefore, the motor has a smaller size, and the stator winding is on the outside and directly connected to the shell, with superior heat dissipation performance. The outer rotor generally uses a label magnet structure, and the air gap magnetic density is between 0.6-0.8T, which makes it difficult to improve the magnetic field strength. The motor winding is the main source of heat, and the outer rotor motor winding is wrapped inside the rotor, which makes heat dissipation difficult. An open-type shell must be used to enhance heat dissipation and reduce the protection level.

Overall, the inner rotor permanent magnet brushless motor fan is superior to the outer rotor motor fan in terms of material installation, motor performance, and heat dissipation.

The second difference between the two lies in their dustproof level: the inner rotor motor has good sealing performance with a protection level of up to IP64, which prevents water and dust from entering and eliminates the need for heat dissipation holes. The inner rotor motor shell has reserved heat dissipation fins, which perform well and prevent demagnetization due to poor heat dissipation. The inner rotor permanent magnet direct-drive motor is equipped with sensors to detect the motor temperature and automatically protect the motor. On the other hand, the outer rotor motor requires the reservation of heat dissipation holes due to structural reasons, making it prone to dust and water ingress, leading to short circuits and motor burnout. Although some industrial ceiling fan manufacturers may use a cover to enhance visual appeal, the heat dissipation holes cannot be avoided. Moreover, the outer rotor motor only has three power cables and lacks a temperature sensor, making it impossible to achieve over-temperature protection, which affects the motor's service life.

The fourth difference is in the motor installation method: the excellent structural design of the inner rotor motor allows the suspension rod and motor to be integrated into one unit, ensuring firm installation. The bearing only needs to bear the weight of the fan blades and is much lighter than that of the outer rotor motor. Therefore, the bearing of the inner rotor motor is more durable with less load and less wear, leading to low lubrication requirements and longer service life. In contrast, the outer rotor motor requires the suspension rod to bear the weight of the entire fan, including the motor, fan blades, and lateral torque generated by the wind during operation. Therefore, the bearing of the outer rotor motor must bear more weight and is subject to faster wear, leading to higher lubrication requirements and shorter service life.