Enter the voltage, back e.m.f. , and current into the calculator to determine the armature resistance.

## Armature Resistance Formula

The following equation is used to calculate the Armature Resistance.

Ra = (V-E) / Ia
• Where Ra is the armature resistance (ohms)
• V is the voltage (volts)
• E is the back e.m.f (volts)
• Ia is the armature current (amps)

To calculate the armature resistance, subtract the back e.m.f from the voltage, then divide by the armature current.

## What is Armature Resistance?

Definition:

An armature resistance is the total resistance seen in motor with an armature current, voltage, and back e.m.f..

## How to Calculate Armature Resistance?

Example Problem:

The following example outlines the steps and information needed to calculate Armature Resistance.

First, determine the voltage. In this example, the voltage is a standard 120 volts.

Next, determine the back e.m.f. The back e.m.f. is found to be 104 volts.

Next, determine the current. In this example, the armature current is calculated to be 15 amps.

Finally, calculate the armature resistance using the formula above:

Ra = (V-E) / Ia

Ra = (120-104) / 15

Ra = 1.066 ohms.