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PC Fan Tutorial
This is an image of BLDC (brusheless direct current) Fan motor in action. The rotor is made of permanent magnets and the stator is an electromagnet. This is a four pole two phase bldc motor. All of the four poles of the stator are active in both phases. The principles of how it works. When the rotor reaches a certain position the hall sensor(wich senses magnetic field) reverses the polarity of the stator. This is an outspinner where the rotor is outside and around the stator. Outspinners are slower from their counterparts inspiners where the rotor is inside the stator.
Stator is wired with two parallel wires treated as one (when wireing). When you look at the stator pole from a side one of the neibhour poles is winded clockwise the other counter clockwise. When the wireing is done the begining of one wire and the end of the other are conected together. This cind of winding combined with the driver gives the same result as if it was one wire with right angle shaped alternating current trough it.
The driver combined with the cind of winding reverses current trough elecromagnet(or the stator) when hall sensor senses certain rotor position.
No Zero Moment
The stator is shaped in a maner that one side of the stator pole(or tooth) is nearer to the rotor then the other. This sets the position of the rotor when the motor is off to just over the position that trigers the hall sensor. Also when the motor is running this pushes (allong with the momentum) the rotor over that position. Magnetic equilibrium position is offsetted for electromagnet turned on and off.