- Joined Nov 29, 2015
Hello guys. I have been looking at the DC shunt motor and I got a question. That is the Back emf formula formula E= (P.N.Z.Ø)/60A. Lets derive this formula to see the speed relationship between flux and we get N=E/kØ , k being constant that we cannot change k=PZ/60A. Okay so looking at the speed and flux relationship it is clear that the speed of the DC shunt motor is increasing because they are inversely proportional. But at the same time, Decreasing flux means decrease in Back emf because they are directly proportional to one another. If we look at the Voltage equation V=Eb-Ia*Ra . Va being total voltage, Eb - back emf and Ia and Ra armature current and resistance. So if back Emf is reduced , current must increase to keep ratio the same. So the increasing current should mean that the speed has gone down. So thats why it is confusing to understand. Why the Speed of the motor does not remain the same If the Flux is forcing motor to rotate faster but at the same time increased current is forcing it to rotate slower? Or am I confusing the Armature current with the Field current?