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The formula to calculate the armature resistance (R_a) of a Permanent Magnet DC (PMDC) motor is not derived from a single universal formula due to the complexity and variables involved, such as the material of the windings, the size of the motor, and the winding configuration. However, a general approach to determine the armature resistance involves using the following relationship:
[ R_a = frac{V – E_b}{I} ]
Where:
– (R_a) is the armature resistance.
– (V) is the applied voltage across the motor terminals.
– (E_b) is the back EMF (Electromotive Force) generated by the motor.
– (I) is the current flowing through the armature.
This equation stems from the basic principles of electrical circuits applied specifically to the context of a PMDC motor. (E_b) can also be determined under running conditions by measuring the voltage across the motor when it is unloaded (no mechanical load applied to the shaft) and operating at a known speed.
For direct calculation or measurement of (R_a) without considering (E_b), it can be done through a simple ohmmetric measurement when the motor is not running. This method involves disconnecting the motor from its circuit and using an ohmmeter to measure the resistance directly across the armature windings.
Remember, the precise calculation or determination of armature resistance can vary based on the specific motor design and the methods available for measurement