Brushed or Brushless Motors?

If you’re having trouble deciding between opting into a brushed or brushless motor design for your next electronic appliance, this article is for you.

The first thing you need to understand about brushless vs. brushed motors is that one uses DC while the other uses AC. DC or direct current motors were more conventional for a while, but now AC motors are starting to replace them because they’re more efficient and reliable.

brushed motorDC motors use two wire windings and two permanent magnets. The coils are powered from the commentator and brushes, which are parts I’ll get into later. When the rotor complete a full cycle, the current that runs through each winding changes direction one time. This is the same as each electromagnet changing its magnetic polarity once. the windings of the two magnets are wound in reverse directions, so when one electromagnet is North, the other is South, and vice versa.

So now back to the commutator and the brushes; these guys are responsible for changing the magnetic field of the two electromagnets according to the position of the rotor. The brushes are two pieces of metal that act as springs. On one side they have a piece of conductive carbon, and on the other they have the pin through which the power supply reaches the motor. The brushes are pushed against the commutator, which is just a metallic ring that’s fixed on the shaft of the motor and divided into two semi-rings. Each semi-ring has one pole of each coil. As the commutator’s semi-rings rotate on the shaft, the poles of the power supply provided to the coils are forced to change because the brushes are fixed to either the positive or negative terminals. This changes the poles of the electromagnetic coils and forces them to continue to rotate.

Brushless motors employ a simpler design in which a magnetic field must rotate around a set of stationary wire coils by turning a shaft. The shaft’s rotation causes AC voltage to be produced across the wire coils.

Brusless motors avoid the necessary making and breaking of electrical contact with am moving coil that DC motors necessitate; that means AC motors are way less vulnerable to sparking and over heating.

brushless motorWhat other advantages does AC have over DC? To discuss this we must first discuss the process of mutual induction. Mutual induction describes the process whereby two or more coils of wire are placed so that the changing magnetic field created by one induces a voltage in the other. That means if there’s two mutually inductive coils and one is energized with AC, AC voltage will then become induced in the other coil. When this is done, the device is known as a transformer.

Transformers are extremely important because they make it possible to step voltage up or down from the powered coil to the unpowered coil. Keep in mind that the AC voltage induced in the unpowered “secondary” coil is equal to the AC voltage across the powered “primary” coil multiplied by the ratio of the secondary coil turns to primary coil turns. Thus, by increasing or decreasing coil turns, voltage can be increased and decreased accordingly.

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