Back EMF of Motors: Constant or Variable?

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Discussion Overview

The discussion revolves around the concept of back electromotive force (EMF) in motors, specifically whether it is treated as a constant or variable value in problem-solving contexts. Participants explore the implications of this treatment in relation to motor operation, current variability, and simplification of problems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the rationale behind treating back EMF as a constant despite variable current, suggesting it may be for simplification purposes.
  • Another participant seeks clarification on the assumption of constant motor RPM in relation to back EMF and current changes.
  • A participant notes that in some formulations, back EMF and resistance are treated as constants while acknowledging that current decreases over time, raising questions about the validity of this assumption.
  • There is a suggestion that simplifying the problem may be a deliberate choice to facilitate understanding or analysis.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the treatment of back EMF as constant, with some proposing it is a simplification while others seek further clarification on the implications of this assumption. No consensus is reached on whether this approach is valid in practical scenarios.

Contextual Notes

Limitations include the dependence on specific problem contexts, the assumption of constant motor RPM, and the potential effects of energy storage in the supplying coil, which may not be universally applicable.

Who May Find This Useful

This discussion may be of interest to those studying electrical engineering, motor control, or anyone involved in the analysis of motor performance and back EMF characteristics.

brainyman89
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i am wondering why in some problem they are regarding back emf of a motor as a constant value that characterizes the motor although current is sometimes variable? i guess the reason is for simplifying the problem, what do u think? can this occur in reality?

thanks for helping.
 
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Constant motor rpm?

Can you give more information?
 
Antiphon said:
Constant motor rpm?

Can you give more information?

they are considering that E=Ir+E' where E'(the back emf) and r are constants although the motor is supplied by a coil that has previously stored energy. so i is not constant, it is decreasing to zero, however they considering that the motor functions normally as E>E', and E' is always constant to each motor.

Anyway, i think your justification that they are using "constant motor rpm" could work here.
 
Could it be that they are trying to make the problem easier?
 

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