The_UnforgiveN
New Member
Hi all..
I've confused
Now, we have a brush DC motor. We show that in a circuit as RLE load, am I right? R-> internal resistance, L -> inductance due to armature coils, E -> back emf due to rotation.
OK, lets take a look to the process.
Assume that I've powered the motor. At that instant, current is at its max because of zero speed of armature. During the speed up, back emf occurs and opposes the main supply voltage. At this time current begns do decrease. First question; when current decreases what happens to inductor, due to dI/dt change? Does inductor forms another back emf that opposes the first created back emf? Because it tries to maintain current?
Later at the instant we cut the power off, some says that very large back emf occurs and damages the switch if we have not any flyback diode. Another question; what's the origin of that huge back emf? In my mind, if we cut the power off, main supply voltage becomes zero and only voltage occurs due to still rotating armature. And this cannot be larger than main supply voltage.
If you say that, this huge emf forms because of the inductor (dI/dt), why there's no emf like this at the begining of the procedure (when powering the system)
whatever, can you enlight me a bit I need roles of inductor and armature speed in creation of the back emf during normal process and at the instant power cut off.
Thank you very much
I've confused
Now, we have a brush DC motor. We show that in a circuit as RLE load, am I right? R-> internal resistance, L -> inductance due to armature coils, E -> back emf due to rotation.
OK, lets take a look to the process.
Assume that I've powered the motor. At that instant, current is at its max because of zero speed of armature. During the speed up, back emf occurs and opposes the main supply voltage. At this time current begns do decrease. First question; when current decreases what happens to inductor, due to dI/dt change? Does inductor forms another back emf that opposes the first created back emf? Because it tries to maintain current?
Later at the instant we cut the power off, some says that very large back emf occurs and damages the switch if we have not any flyback diode. Another question; what's the origin of that huge back emf? In my mind, if we cut the power off, main supply voltage becomes zero and only voltage occurs due to still rotating armature. And this cannot be larger than main supply voltage.
If you say that, this huge emf forms because of the inductor (dI/dt), why there's no emf like this at the begining of the procedure (when powering the system)
whatever, can you enlight me a bit I need roles of inductor and armature speed in creation of the back emf during normal process and at the instant power cut off.
Thank you very much