How DC Motor work ?? Motor Principle

An electric motor is a machine which convert electrical  energy   in to mechanical energy .Its principle is that when a current carrying conductor is place in a magnetic field its experience a force which direction is given by Fleming left hand Rule and magnitude is given by F=BIL Newton

There is no difference between the D.C Generator and D.C Motor .The same dc Generator can be used as a Dc motor .

When a voltage is applied to the Dc motor ,current will pass in to positive brushes  through commutator into the armature winding .Actually the motor armature winding is identical to that of Generator armature winding .Therefore the conductor under north pole carry current in one direction and conductor under south pole carry current in opposite  direction.When armature carry current its produce magnetic field which will interact with the main  field as a result there is a force developed on the conductor which tend to turn the armature or rotor .

The  rotating armature conductors ina motor cut the flux from the poles, so an emf is induced in armature .According to the Lenz’s Law tgis emf opposed the applied emf to the motor   and this emf is known as Back emf Eb and is given by

 Where          Z=Total No of armature conductors

              A=No of Parallel path in armature

              N= Speed of rotation

              P=No of Pole

               $=Flux per Pole

Voltage Equation of Motor

The basic Voltage equation of motor is expressed by


Where         v= P.d applied ti the brushed in volt

             =Armature resistance

           Armature current

Eb is Zero when the motor is at standstill or not start.


The torque of Dc motor is given by

         F =2πr X N Watts

            = Torque  X Angular Velocity

        P= T.ω watts

        Where f  =circumferential force (Newton)

                     r=radius of the pulley

                    Torque  =  Fx 2 π r  joule  

Armature Torque

Where N is the speed in RPM

Shaft Torque

Lost Torque:


Speed of Motor

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