CHAPTER 17 ■ DC MOTORS
Living Longer Without Brushes
Brushes are usually the first part to wear out on a brush motor. The lack of brushes on a brushless motor
means dramatically increased lifespan and significant reduction in electrical noise. The lack of brushes
eliminates sparking, and as such may be important in some scientific or hazardous situations.
For these reasons, brushless motors are very popular for computer fans. The brushless motor fan can
run constantly for the life of the computer and the fan doesn’t generate significant electrical noise that could
interfere with the computer’s digital operations.
Switching with Brushless Circuitry
Since a commutator doesn’t exist on a brushless motor, the windings are not mechanically switched as the
rotor rotates. Instead, a non-trivial circuit (see Figure 17-9) monitors electrical current or the position of the
rotor’s magnet to electronically determine when to flip the flow.
Figure 17-8. Guts of a brushless motor for a fan: (left to right) rotor with permanent magnet, stator with
armature, pair of bearings, compression spring, and a retaining ring
Figure 17-9. Circuit built into brushless motor