Brushless DC Motor


Brushless DC motor do not have brush which may be described as electronically commuted motor. in brushless motor armature is fixed and permanent magnet are used as the rotating part which is rotate around the fixed armature.

A brushless DC motor is considered to be a high performance motor that is capable of providing large amounts of torque over a wide speed range. So The Brushless DC (BLDC) motor is the ideal choice for applications that require high reliability, high efficiency, and high power-to-volume ratio.

In a brush DC motor, the motor assembly contains a physical commutator which is moved by means of actual brushes in order to move the rotor. With a BLDC motor, electrical current powers a permanent magnet that causes the motor to move, so no physical commutator is necessary.The rotor is constructed from permanent magnets with two-to-eight N-S pole pairs. More magnet pairs increase torque and smooth out so-called torque ripple, evening the power delivery from the motor.

Working principle of brushless DC motor :-

The basic principles for the brushed DC motor and for brushless DC motor are same. DC motor has only two basic parts: rotor and the stator. The rotor is the rotating part and has rotor magnets and stator is the stationary part and contains stator windings. In the brushed motor, rotating armature is inside and permanent magnets are at the outside. when supply is given  armature will rotate and its produced the magnetic field around the armature. brushes  will change the polarity of the pole to keep the rotation on of the armature.In brushless DC motor permanent magnets are fitted in the rotor and move the electromagnets to the stator. A brushless DC motor is highly reliable since it does not have any brushes to wear out and replace.

There are two basic types of brushless DC motor designs:-

  1. Inner rotor and
  2. Outer rotor design.

The design is different of both types, but their working principle are same.

  • Outer rotor :-

      outer rotor design

In an outer rotor design, the windings are located in the core of the motor. The rotor magnets surround the stator windings as shown in fig. The rotor magnets act as an insulator, thereby reducing the rate of heat dissipation from the motor. Such type of designed  typically operate at lower duty cycles or at lower rated current and has low clogging torque.

  • Inner rotor :-

    inner rotor design

    In an inner rotor design, the stator windings surround the rotor and are affixed to the motor’s housing as shown in fig. The advantage of an inner rotor construction is that, A motor’s ability to dissipate heat directly impacts its ability to produce torque. due to this reason, inner rotor designed motor produces a large amount of torque and validly used. this type of design is has lower inertia.

Advantages of Brushless DC Motor :-

  1. There is no sparking and much less noise during operation.
  2. Inner rotor Brushless DC motors have low rotor inertia, allowing them to accelerate, decelerate, and reverse direction quickly.
  3. BLDC motors have the highest running torque per cubic inch of any DC motor.
  4. BLDC motor can operate at high-speed under any condition.
  5. As do not have brushes , the mechanical energy loss due to friction is less which increase efficiency.
  6. BLDC motors are more reliable.
  7. Better heat dissipation capabilities, hence cooling is not require.

Disadvantages of Brushless DC Motors:-

  1. Electric controller is required to keep the motor running. so It offers double the price of the motor.
  2. High initial cost, Need for commutating device  like an encoder and a drive or controller.
  3. It is expensive because, the permanent magnets.


The Brushless DC motor is the ideal choice for applications that require high reliability, high efficiency, high power-to-volume ratio and high starting torque.

  • Heating and ventilation
  • Industrial engineering
  • Transport


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