What is the formula for the armature resistance in PMDC motor?

The formula for armature resistance in a Permanent Magnet DC (PMDC) motor is not a single universal formula that can be applied directly because it involves understanding the specific characteristics of the motor. However, the armature resistance (Ra) can typically be determined by measuring the resistance across the armature windings with an ohmmeter when the motor is not running. Additionally, manufacturers may provide this value in the motor’s specifications.

In a practical scenario, to calculate or measure the armature resistance, the general approach would involve using Ohm’s Law, which is V = I*R, where V is the voltage across the armature, I is the current flowing through the armature, and R is the resistance of the armature. If you directly measure the voltage across the armature and the current flowing in the circuit with the motor at a standstill (to prevent the back EMF from affecting your measurements), you can then rearrange the formula to solve for R (armature resistance). That is, R = V/I.

Remember, this measurement should be done carefully and preferably with the motor disconnected from its power source to ensure safety and prevent damage to the motor or the measuring equipment.