The brushless DC electric motor (also known as BL motor, BLDC motor or electronically commutated motor) is one of the synchronous motors that are powered with the use of DC electricity. This is possible through switching power supply or an inverter. This produces AC current to drive the motor’s phases through closed look controllers. A brushless motor controller offers current pulses to the windings of the motor to control torque and speed.
The build of the brushless motor system is really similar to that of the permanent magnet synchronous motor. However, it can also be an induction motor or a switched reluctance motor.
Brushless DC electric motors are usually preferred to the brushed motors because of the high power-to-weight ratio available, electronic control and high speed. Such a motor is used in different industries, in places like hand-held power tools, vehicles and computer peripherals.
Brushless DC Electric Motors Versus Brushed Motors
One thing that few people know is that the brushed DC motor was invented during the nineteenth century. It is much more common than you might think. In fact, it is the reason why solid state electronics became a reality in the sixties.
The electric motor is developing torque through alternating rotating magnet polarities. Magnets are attached to a rotor, which is the machine’s rotating part. Stationary magnets are also present on the included stator, a part that surrounds a rotor.
Both sets or just one of the used magnets are actually electromagnets. They are made out of a wire coil that is wound around a core made out of iron. DC current runs through the wire. This creates a strong magnetic field that offers power necessary to run a motor.
Every single time a rotor rotates by half a turn, the south and north poles reverse their positioning. In the event that magnetic field remains the same, torque reversal happens on every single half a turn. Rotors would not be able to turn.
The DC motor changes electric current going through windings every half a turn so that torque can be created in a single direction. This little modification reverses magnetic field direction while the rotor is turning. Rotor torque simply goes towards the exact same direction.
In the brushed motors there is a commutator made out of a cylinder that is rotating and made out of many metal contact segments placed on the rotator. The use of the commutator brings in some disadvantages that were eliminated through the development of brushless DC electric motors. The commutator’s disadvantages are:
- The brush’s material always wears down because of friction.
- Brushes have to be replaced.
- Power losses appear because of friction associated with brushes.
- Sliding brush contract resistance causes voltage drops.
- Repeated current switching leads to sparks at the contacts of the commutator.
Nowadays, DC brushed motors were mostly replaced with brushless motors. The brushed motors are just used in the really low power applications or in applications where DC is available. The drawbacks mentioned above highly limit use even in such applications.