Differences Between Brushless and Brushed DC Motors
Brushless motor vs Brushed motor
For several years now, we’ve been seeing brushless motor dominating advance power tool industry. Does it really make difference to use brushless over brush motor? Yes, absolutely. There are significant difference between them.
Let’s look at the basics of DC motor. Dc motor is all about magnets and electro-magnetism. Opposely charged magnets attract each other. Main idea behind DC motor is keep opposite charge of rotating component attracted towards non-moving magnets (the stator) in front of it so it generates constant pull. This forward pull movement produced by physical behavior of electromagnetism.
Principle:
It is based on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force whose direction is given by Fleming’s Left-hand rule and whose magnitude is given by
Force,F = B I l newton
Where B is the magnetic field in weber/m2.
I is the current in amperes and
l is the length of the coil in meter.
The force, current and the magnetic field are all in different directions.
Construction differences:
Brushes inside electric motors are used to deliver current to the motor windings through commutator contacts. Brushless motor not have current carrying commutators. The field inside a brushless motor is switched via an amplifier triggered by commutating device, such as an optical encoder.
A brushed DC motor uses a configuration of wound wire coils, the armature, acting as a two-pole electromagnet. The current’s directionality is reversed twice per cycle by the commutator, a mechanical rotary switch. This facilitates flow of the current through the armature; thus, the electromagnet’s poles pull and push against the permanent magnets along the outside of the motor. The commutator then reverses the polarity of the armature’s electromagnet as its poles cross the permanent magnets’ poles.
A brushless motor, by contrast, utilizes a permanent magnet as its external rotor. In addition, it uses three phases of driving coils and a specialized sensor that tracks rotor position. As the sensor tracks the rotor position, it sends out reference signals to the controller. The controller, in turn, activates the coils in a structured way – one phase after the other.
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