# What if this happened?(theoretically )

Discussion in 'General Electronics Discussion' started by Dretron, Dec 18, 2012.

1. ### Dretron

101
0
Jun 9, 2012
I was wondering if the magnetic field of a permanent magnet (B) became very strong.
That the B-EMF would be higher than the inputed EMF what would happen? To the motor,electromagnets, etc...?

In theory what would happen? I thought the input EMF would increase the current to resist the higher B-EMF?

Dre.

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,505
2,852
Jan 21, 2010
If the back EMF is higher then you have a generator, if lower, a motor.

Back EMF can only exceed the voltage applied if the voltage applied is reduced or if some external source of power is driving the shaft.

3. ### Laplace

1,252
185
Apr 4, 2010
When the generated back-EMF equals the applied EMF there would be no current flow, hence no torque produced by the motor. With no torque the motor slows down, producing less B-EMF so that more current flows. But with a stronger magnetic field the same B-EMF will be produced at a slower RPM.

4. ### Dretron

101
0
Jun 9, 2012
Nope, say you didn't decrease the input voltage or applied a power to move the shaft, just increased the magnetic force of a magnet in a motor. That would significantly increase the B-EMF.

And if the B-EMF was greater the motor will slow down because there is no input torque, and thus the motor would turn into a generator feeding back current to the source. But In cause a source is constantly applying voltage and current to the electromagnet and the B-EMF is greater than that input, Im imaging that the over heating would cause a major damage and something will happen but I can't imagine what exactly...