As a common drive device for small household appliances, the shaded pole motor has significant differences in efficiency and noise between its salient pole and hidden pole structural designs. The following is an in-depth analysis of the differences in performance between the two based on the motor structure and working principle.
From the perspective of structural design, the stator core of the salient pole shaded pole motor has a prominent magnetic pole, and a small slot is opened on one side of each magnetic pole. A short-circuit copper ring is embedded in the slot, that is, the shaded pole winding, and the winding is centrally wound. This structure is simple and intuitive, the manufacturing process is relatively easy, and the cost is low. The stator core of the hidden pole shaded pole motor has no obvious protruding magnetic poles, and the magnetic poles are evenly distributed in the core slots, and the winding is distributed. The hidden pole structure is more compact and can make better use of space, but its manufacturing process is relatively complex and requires high processing accuracy. The essential difference in structure lays the foundation for the different performances of the two in terms of efficiency and noise.
In terms of efficiency performance, the salient pole shaded pole motor has an uneven magnetic field distribution and a large magnetic resistance due to the protruding magnetic poles and uneven air gap. During operation, the larger magnetic resistance increases the hysteresis loss and eddy current loss, and the energy is lost more during the conversion process, thereby reducing the motor efficiency. At the same time, the centralized winding method makes the winding end longer, which increases the copper loss. Taking the common household fan as an example, the efficiency of the salient pole shaded pole motor is generally around 40% - 50%. In contrast, the non-salient pole shaded pole motor has a uniform air gap and distributed winding design, and the magnetic field distribution is closer to the ideal state, the magnetic resistance is small, and the hysteresis loss and eddy current loss are relatively low. The distributed winding effectively shortens the length of the winding end and reduces the copper loss. Moreover, the non-salient pole structure can better adapt to different load changes and maintain high efficiency under partial load conditions. Therefore, the efficiency of the non-salient pole shaded pole motor can usually reach 55% - 65%, which is significantly better than the salient pole type in terms of energy efficiency.
From the perspective of the impact of starting performance on efficiency, the salient pole shaded pole motor relies on the induced current generated by the short-circuit ring to form a moving magnetic field to achieve self-starting. However, this starting method has the problem of small starting torque, which is generally only 30% - 50% of the rated torque. In order to obtain sufficient starting torque, the motor requires a large current at the moment of starting, which not only increases the energy loss during the starting process, but also causes a large impact on the power supply, affecting the overall efficiency of the motor. Although the starting principle of the hidden pole shaded pole motor is similar to that of the salient pole motor, due to its more uniform magnetic field distribution and more reasonable winding design, the starting torque is relatively large, generally reaching 50% - 70% of the rated torque. The smaller starting current requirement makes the hidden pole motor have lower energy loss during the starting process, and can enter the efficient operation state faster, further improving the overall efficiency.
In terms of noise generation, the uneven magnetic field distribution of the salient pole shaded pole motor will cause large fluctuations in electromagnetic force. When the motor is running, this fluctuating electromagnetic force will cause periodic vibrations between the stator and the rotor, thereby generating electromagnetic noise. The protruding magnetic poles and concentrated windings are also prone to mechanical resonance, exacerbating the noise problem. Especially when running at high speed, the noise is more obvious, and its noise frequency is mainly concentrated in the medium and low frequency bands, and the general sound pressure level is between 55 and 65 decibels. In addition, during the rotation of the salient pole motor, the rotor will be affected by unbalanced magnetic pull due to uneven air gap, which will cause accelerated bearing wear and generate additional mechanical noise. The shaded pole motor has a uniform magnetic field and small electromagnetic force fluctuations, so the electromagnetic noise generated is relatively low. The distributed winding and uniform air gap design reduce the possibility of mechanical resonance, making the motor run more smoothly. At the same time, the rotor of the shaded pole motor is subjected to a relatively balanced magnetic pull, with less bearing wear and correspondingly reduced mechanical noise. Its noise frequency is mostly distributed in the medium and high frequency bands, and the human ear is less sensitive to noise in this frequency band. The sound pressure level is generally between 45 and 55 decibels, and it is quieter during operation.
In different application scenarios, the impact of the difference in efficiency and noise between the two is more significant. In scenarios where noise requirements are not high and cost is sensitive, such as ordinary industrial exhaust fans, cheap heaters and other equipment, the salient pole shaded pole motor is widely used due to its low cost and simple structure. Although the efficiency and noise performance are not good, it can meet basic functional requirements. In scenarios with high requirements for noise and efficiency, such as household silent fans, microwave turntable motors, air purifiers and other home appliances, the hidden pole shaded pole motor has become the first choice due to its high efficiency and low noise, which can provide users with a better user experience.
From the perspective of technological development trends, as people's requirements for energy efficiency and quietness of home appliances continue to increase, the application prospects of the hidden pole shaded pole motor are broader. R&D personnel have further improved the performance of hidden pole motors by optimizing magnetic circuit design, adopting new magnetic materials, and improving winding processes. For example, the use of amorphous alloy materials to make iron cores can greatly reduce hysteresis losses; optimizing winding winding methods, increasing slot fill rate, and reducing copper losses. For salient pole shaded pole motors, new improvement directions are also being explored, such as trying to reduce noise and improve efficiency by improving short-circuit ring design and optimizing pole shape, but due to structural limitations, the room for improvement is relatively limited.
There are obvious differences in efficiency and noise between the salient pole and hidden pole structural designs of shaded pole motors. The hidden pole structure has excellent performance in efficiency and noise control due to its more reasonable design, which is more in line with the development needs of modern home appliances. Although the salient pole structure has certain shortcomings, it still has its application value in specific scenarios. Understanding the differences between the two will help to reasonably select motor types in different application scenarios and promote the improvement of the performance of small home appliances.
