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basics of motor why the motor takes high current when it is off

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krishik

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i am using the BLDC motor fan and controlling the speed of the fan using PWM
i want to know some basic theory about the motors
i taken the 12V motor ,i connected the power supply and increasing the supply voltage by using the power supply form 0 t0 12V
when i given the supply from 0 to 3.3 volts the fan it taking the huge current of 460mA and motor is not running and fan is not starting .
when i given 3.4V the fan is starting and motor is running the current is suddenly dropping from the 460mA to 100mA and settles at that current .
why the motor is taking high current when it is off
 

In general, motors take much more current when they are stopped than when they are running. This is because, when a motor is running, the motion produces a "back-EMF": a voltage which is created from the motor basically acting like a generator while it spins. Due to its polarity, this back-EMF reduces the current flowing into the motor (effectively, the voltage driving the motor becomes Vsupply - Vbemf; less voltage means less current). When a motor is stopped, there is no back-EMF to impede the current flow, so you simply have 3.3V directly across the motor windings; lots of current flows then.
 
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