## Voltage And Power Equations of a DC Motor

**Voltage Equation of the DC Motor**

Input Voltage provided to the motor armature can perform the following two tasks:

Obtain control on Back E.M.F E

_{b }of the Motor.Provide supply to the Ohmic I

_{a}R_{a}drop.i.e.

**V = E**

_{b}+ I_{a}R_{a ………………….}(1)Where

E

_{b }= Back E.M.FI

_{a}R_{a }= Armature Current X Armature ResistanceThis is called “Voltage Equation of the DC Motor”.

**Power equation of a DC Motor**

Multiply both sides of Equation (1) by I

_{a}, we get,**VI**

_{a}= E_{b}I_{a }+I_{a}^{2}R_{a}………. (2)where,

**VI**

_{a }=**Input Power supply (Armature Input)**

**E**

_{b}I_{a }=**Mechanical Power developed in Armature (Armature Output)**

**I _{a}^{2}R_{a}= **

**Power**

**loss**

**in**

**armature**

**(Armature Cupper (Cu) Loss)**

Hello sir I want the full equation…..

In the article “Voltage And Power Equations of a DC Motor” the iron losses are not mentioned.

Those losses can not be neglected.

Would be interesting to see those incorporated in the calculations.

I need power knowledge for the selection of motors and VFD.