3.3.5 Discuss about Brush-less Motor

3.3.5 Discuss about Brush-less Motor

•      The mechanical "rotating switch" or commutator/brushgear assembly is replaced by an external electronic switch synchronised to the rotor's position. 

•      Brushless motors are typically 85–90% efficient or more, efficiency for a brushless electric motor. 

•      Midway between ordinary DC motors and stepper motors lies the realm of the brushless DC motor. 

•      Built very similar to stepper motors, these often use a permanent magnet external rotor, three phases of driving coils 

•      Sensors to sense the position of the rotor, and associated drive electronics. 

•      Used where precise speed control is necessary, as in computer disk drives or in video cassette recorders, the spindles within CD, CD-ROM (etc.) drives, and mechanisms within office products such as fans, laser printers and photocopiers.

 (source: http://en.wikipedia.org/wiki/Electric_motor)

VIDEO: How Brushless Motor Works!

Several advantages over conventional motors:

•      Much cooler than the equivalent AC motors. 

•      Without a commutator to wear out, the life of a DC brushless motor can be significantly longer compared to a DC motor using brushes and a commutator. 

•      Commutation also tends to cause a great deal of electrical and RF noise; without a commutator or brushes, a brushless motor may be used in electrically sensitive devices like audio equipment or computers.

•      The same Hall effect sensors that provide the commutation can also provide a convenient tachometer signal for closed-loop control (servo-controlled) applications. In fans, the tachometer signal can be used to derive a "fan OK" signal as well as provide running speed feedback.

•      The motor can be easily synchronized to an internal or external clock, leading to precise speed control.

•      Brushless motors have no chance of sparking, unlike brushed motors, making them better suited to environments with volatile chemicals and fuels. Also, sparking generates ozone which can accumulate in poorly ventilated buildings risking harm to occupants' health.

•      Brushless motors are usually used in small equipment such as computers and are generally used in fans to get rid of unwanted heat.

•      They are also acoustically very quiet motors which is an advantage if being used in equipment that is affected by vibrations.

•      Modern DC brushless motors range in power from a fraction of a watt to many kilowatts. Larger brushless motors up to about 100 kW rating are used in electric vehicles. They also find significant use in high-performance electric model aircraft.

  (source: http://en.wikipedia.org/wiki/Electric_motor)

Figures: Fans in computer usually uses brushless dc motors

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