Back EMF of Motors: Constant or Variable?

AI Thread Summary
The discussion centers on the treatment of back EMF in motors, where it is sometimes considered a constant value despite variable current. This simplification is often used to facilitate problem-solving, as it assumes that back EMF remains constant while the current decreases. Participants question whether this assumption holds true in real-world scenarios, particularly when motors are supplied by coils with stored energy. The concept of "constant motor RPM" is suggested as a potential justification for this approach. Overall, the conversation highlights the balance between theoretical models and practical applications in motor behavior.
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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