In order to make the operation more reliable, more efficient and less noisy, the recent trend has been to use brushless dc motors.
They are also lighter compared to brushed motors with the same power output. The brushes in conventional dc motors wear out over time and may cause sparking. Thus the brushed dc motor should never be used for operations that demand long life and reliability.
Let`s see how a brushless dc motor works:
The rotor of a BLDC motor is a permanent magnet, the stator has a coil arrangement as shown by applying DC power to the coil, the coil energize and become an electromagnet, the operation of a BLDC is based on the simple force interaction between the permanent magnet and the electromagnet, in this condition when the coil A is energized the opposite poles on the rotor and stator are attracted to each other. As the rotor nears coil A, coil B is energized, as the rotor near coil B, coil C is energized, after that coil as energized with the opposite polarity, this process is repeated and the rotor continues to rotate.
A humorous analogy to help remember it is to think about BLDC operation like the story of the donkey and the carrot, where the donkey tries hard to reach the carrot but the carrot keeps moving out of reach. Even though this motor works, it has one drawback, you can notice that at any instant only one coil is energized. The two dead coils greatly reduce the power output of the motor.
Here is the trick to overcome this problem. When the rotor is in this position, along with the first coil which pulls the rotor, you can energize the coil behind it in such a way that it will push the rotor. For this instant a same polarity current is passed through the second coil, the combined effect produces more torque and power output from the motor, the combined force also makes sure that a BLDC has a beautiful constant torque nature, with this configuration two coils need to be energized separately, but by making a small modification to the stator coil, we can simplify this process just connect one free end of the coils together.
When the power is applied between coils A and B, let`s note the current flow through the coil, it`s just like the separately energized state, that`s how a BLDC works but you might have some intriguing doubts in your mind, how do I know which stator coils to energize, how do I know when energizer so that I will get a continuous rotation from the rotor, in a BLDC we use an electronic controller for this purpose. A sensor determines the position of the rotor and based on this information the controller decides which coils to energize, most often a Hall effect sensor is used for this purpose. The BLDC design we have discussed so far is known as the out runner type. In runner BLDC design is also available in the market.
We hope you had a nice introduction on the working of BLDC motors.
Thank you!