Brushless motors

Brushless differs from conventional dc motors in the sense that it does not have brushes. Commutation is done using electronic drives to feed power to the stator windings. They consist of a rotor which is in the form of a permanent magnet and a stator that is in the form of polyphase armature windings. A brushless DC motor can be constructed in two ways; one is by placing the rotor outside the core and the other is by placing the rotor inside the core.

How a brushless motor works

Brushless motors are driven by electronic drives that switch the supply voltage between the stator windings while the rotor turns. There is a transducer that monitors the position of the rotor as it turns and conveys the information to an electronic controller. The controller then decides which stator winding to be energized based on the position of the rotor. Electronic drives are made up of two transistors each phase which are run by a microprocessor.

The magnetic field induced by the current passing in the stator windings interacts with the magnetic field generated by the permanent magnets as result creating mechanical torque. The electronic drive switches the supply current in a manner to maintain a 90-degree angle between the two interacting fields. The rotor or stator is mounted with hall sensors so as to generate a high or low signal as the rotor passes through. The winding is then energized based on the high and low signals generated by the hall sensor. So as to keep the rotor running, its winding’s magnetic field ought to shift position while the rotor catches up with the stator field.

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A single hall sensor is used for a 4 pole, 2 phase brushless motor. The sensor is embedded on the stator from where it develops high and low signals while the rotor rotates. It is connected to the transistors via a resistor. When a high signal is generated, the transistor connected to the coil starts conducting hence providing a path for current to flow and a result, energizing the coil. The capacitor then charges to full. During a low signal, the transistor does not get any current and so it remains in off condition. The voltage developed around the capacitor, which acts as the supply voltage to the second transistor and coil becomes energized as current passes through it.

Application of brushless motors

Brushless motors have numerous advantages over conventional DC motors hence they have numerous applications. They are found in numerous applications including:

  • Consumer electronics
  • Industrial machines
  • Transportation equipment
  • Heating and ventilation
  • Medical equipment

Brushless have proliferated to virtually every sector of our every day to day lives. However, they are less popular compared to Brush DC motors owing to the fact that they are more expensive. Luckily, keep getting cheaper owing to improvements in materials and design. This has partly contributed to its now growing popularity. It is hoped that their edge over Brush DC motors will go along way to boost its popularity in the sectors where they are yet to be absorbed.

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