Common BLDC Fan Construction

Basic brushless DC motors can be broken into two main components: the rotor and the stator. As implied by its name, the rotor is the rotating part, while the stator is the static construct around which the rotor rotates. The rotor houses permanent magnets, and in the case of a fan motor, the fan blades are attached to it. See the figure below.

Figure 1. Common BLDC Fan Rotor

The motor coils are housed in the stator, which when energized correctly will make the motor turn. In common two-phase BLDC motors, there are typically four coils. See the figure below.

Figure 2. Common BLDC Fan Stator

Torque to turn the motor is produced by the interaction between the magnetic fields created by the energized motor coils and those of the permanent magnets in the rotor. What motor coils should be energized at what time is given by the angular position of the rotor relative to the stator. The act of applying current to the correct coils as the motor turns is called commutation. Information about the orientation of the rotor is most commonly fed back to the motor controller by a Hall effect sensor mounted on the stator.