Motors

# Voltage And Power Equations of a DC Motor

## 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 “Eb” of the Motor.
• Provide supply to the Ohmic IaRa drop.

i.e.

V = Eb + IaRa …………………. (1)

Where

• Eb = Back E.M.F
• IaRa   = Armature Current X Armature Resistance

This is above related is known as “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)

Where,

• VIa = Input Power supply (Armature Input)
• EbIa = Mechanical Power developed in Armature (Armature Output)
• Ia2Ra= Power loss in armature (Armature Copper (Cu) Loss)

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### Electrical Technology

1. Ganesh says:

Hello sir I want the full equation…..

2. R.J.Jochems says:

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.

3. R.Prabhakar Rao says:

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

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