why motor takes the high current at the time of starting

[krishik]

i am using the 12V bldc motor
when it give the 12 V to the motor it taking initially high current and then it settle to the 460mA
why it is taking the high current at the starting

 

[100k]

At starting the back emf is zero therefore, the current is given by V/R where R is armature resistance and it is very small, so current drawn at starting is higher than full load current. As the motor speeds up the back emf is developed which reduces the current drawn from the battery and is given by the eqtn I= (V-E)/R

 

[Baas Rietrot]

I agree with 100k. A motor is an inductive component which uses current to "charge up" similar to a capacitor which uses voltage to charge, this will account for the large current draw at start-up.

 

[betwixt]

Sorry Baas Rietrot but that's nonsense. Nothing 'charges up', it's as 100k states, the result of back emf generation, look up Lenz's Law, it explains what happens. When the motor is stopped or stalled, the current drawn is almost as though the motor is a resistor with value decided by the copper and contact resistance.

Brian.

 

[Baas Rietrot]

With start up you have a low resistance in your inductor being a wire and all. Lenz's law opposes the change in current, backward EMF. A inductor uses current to store energy in a magnetic field.

 

[chuckey]

Also there is energy stored in the rotating mass of the armature, this has to be put in and actually causes the slow accelaration time, and hence the slow rise of the back EMF and the finite time for the current to fall to the "normal" running current.
Frank