Difference Between Brushless DC Motor and Shaded Pole Asynchronous Motor

Brushless motors are typically 85% to 90% efficient, in large part because most of the energy going into the coils actually moves the rotor. The motor is compared with another shaded pole asynchronous motor in the fan to understand the difference in the use of the two motors.

An electromagnet in the stator of a scooter motor induces a magnetism in the rotor. They induce a magnetism in the rotor because, unlike the rotor in a BLDC motor, the rotor in an asynchronous motor does not contain any magnets. The motors that power the cooling fans tend to be brushless or asynchronous motors. Here, we examine the main structural differences between the two motor types and explain the reasons for the significant difference in energy efficiency between the two motors.

Brushless motors are sometimes called electronically commutated motors. Commutation here refers to the act of switching the electrical connection from one motor winding to another, which in a DC motor is usually located in the stator or stationary part of the motor. The rotor then contains magnets with alternating poles. (DC motors with magnets in the rotor are sometimes called outer rotors. There are other possible configurations, but they are not as widely used as outer rotors.)

Brushless DC motors use an electronic controller to sequentially energize the stator windings, turning the stator windings into electromagnets that spin the rotor. First, a set of coils (i.e. one coil and the coil located 180 degrees away from it) will be energized to become an electromagnet. This causes the opposite poles of the rotor and stator to attract each other, when the rotor approaches a energized coil, the next coil is energized, the coil closest to the rotor pole is turned off, and as the rotor spins near the next coil on the stator, the coil closest to the rotor pole The coil will be off. The above always acts on the rotor when the rotor is in operation. And high efficiency is one of the reasons you see fans made from electronically commutated DC motors.

The term "shaded pole" comes from the use of separate small windings in the stator called "shaded coils". The electromagnets in the stator are wound on a small portion of the laminations by a coil shaded coil surrounding the steel laminations. When alternating current is supplied to the main winding, a portion of the generated magnetic flux will be linked to the light-shielding coil. This induces a current in the gobo coil which behaves like a transformer secondary. The induced current in turn produces its own weak flux which lags the flux of the main part of the stator. Therefore, there is a temporal and spatial displacement between the two fluxes. This temporal and spatial displacement sets the conditions for the rotating (or moving) magnetic field. The rotating magnetic field is what starts and keeps the rotor spinning. Some shaded pole motors do not use shaded coils, instead they use a small gap in the laminations, just enough to create the hysteresis field needed to spin the rotor.

The advantage of shaded pole motors is that they are inexpensive because of their very simple construction. But the problem is that they are inefficient, largely due to the lossy link between the shadow coil and the main winding. Shaded pole motors typically have an efficiency of only 15% to 30% and a low power factor.

For applications with only a small fan (shaded pole motors are usually smaller at 40W), low power factor and efficiency may be ok. However, consider an application like a data center, where there are racks and racks and servers and racks, and each server has its own fan. It is not recommended to run several or even thousands of fans all at only 30% efficiency, these applications can really benefit from the use of brushless motor technology and the 90% efficiency it brings.Shaded pole motors, oven motors, range hood motors, dryer motors, air fryer motors, disinfection cabinet motors, built-in oven motors