While electric motors are available in a number of forms, they all work by making the motor’s shaft rotate in the same manner. They function by taking advantage of the attraction and repulsion between the north and south poles of a magnet and the magnetic field produced by an electric current. Motors that use direct current (DC) power supply to rotate the shaft are called DC motors and are divided into brush and brushless (BLDC) types.
Brushes are the internal parts of a DC motor that are utilized alongside a commutator as commutation is one of the major ways that DC motors are able to achieve continuous rotation. As such, DC motors that are equipped with a commutator and brushes are called brushed DC motors, whereas those that use an electronic circuit instead of the commutator and brushes are known as brushless DC (BLDC) motors.
To ensure that the shaft of a DC motor is rotating in the same direction, there must be a mechanism in place to switch the direction of the electrical current flow once every half-rotation, a process that is referred to as commutation. Brushed DC motors can achieve this by using a commutator and brushes that remain in electrical contact as the shaft rotates. Due to this contact, friction and wear is common, requiring that these components receive periodic maintenance. Another problem with the contact between the commutator and brushes is the electrical and acoustic noise that is generated.
In contrast, brushless DC motors eliminate the need for brushes and a commutator by incorporating an electronic circuit that detects the angular position of the shaft. That being said, this configuration eliminates the need for extensive maintenance and reduces noise. To better understand the differences between brushed and brushless DC motors, we will outline each in detail.
What is a Brushed DC Motor?
Brushed DC motors have their coil windings situated inside the rotor. When the rotor rotates, the brush connections switch between commutators, so that the flow of electrical current switches through each coil. This allows the rotor to rotate continuously. Additionally, as brushed DC motors are easy to use and control, many applications benefit from them.
What is a Brushless DC Motor?
By having permanent magnets in the rotor, the brushless DC motor avoids the need for a commutator and brushes. The rotor is kept rotating by detecting the position of the rotor’s magnetic poles and switching the electric current flow through the coils accordingly. For this reason, brushless DC motors necessitate an electronic drive circuit. To detect the rotor shaft position, a hall effect sensor or other magnetic sensor can be used. Hall effect sensors use the hall effect to determine magnetic field strength. As the magnetic field is converted into an electrical signal, the driver can easily detect the position of the permanent magnet and switch the electrical current flow through its coils to keep the motor shaft rotating. In terms of advantages, brushless DC motors exhibit excellent tracking and responsiveness, can run at high speeds, and display a long service life.
Different Types of Brushless DC Motors
Brushless DC motors can be subdivided into two categories, those which have an outer rotor and those which have an inner rotor. With an outer rotor motor, the permanent magnets are located on the rotor which rotates around the exterior of the stator coil windings. An inner rotor motor, on the other hand, has the magnets on the inside and the stator coil windings on the outside.
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