Input Voltage provided to the motor armature can perform the following two tasks:
Obtain control on Back E.M.F Eb of the Motor.
Provide supply to the Ohmic IaRa drop.
V = Eb + IaRa ………………….(1)
Eb = Back E.M.F
IaRa = Armature Current X Armature Resistance
This is called “Voltage Equation of the DC Motor”.
Power equation of a DC Motor
Multiply both sides of Equation (1) by Ia , we get,
VIa= EbIa +Ia2Ra ………. (2)
VIa = Input Power supply (Armature Input)
EbIa = Mechanical Power developed in Armature (Armature Output)
Ia2Ra= Power loss in armature (Armature Cupper (Cu) Loss)