On Feb 22, 2005, at 11:26 AM, Todd Walton wrote:
On Sun, 20 Feb 2005 22:42:27 -0800, Andrew P. Lentvorski, Jr. <[EMAIL PROTECTED]> wrote:And it will induce a current *why*?
Most industrial and consumer motors do not have permanent magnets. In
that case, a turned motor will *not* induce a returned current as there
is no magnetic field to provide a change in flux.
But, if the motor is turning (because it's on), it creates its own magnetic field. When power is cut, the magnetic field collapses, generating electricity.
Right?
Sort of. You are correct that as the magnetic field collapses, it will convert the magnetic field back into an electric field and consequently electric current.
However, this does not depend upon whether or not the motor is turning. If I put too large a load on the motor such that it never turns, the magnetic field will still build up in the coils. When I cut the power, this magnetic field will collapse and generate the back EMF as well. The key factor here is the fact that the internal coils exhibit inductance. This inductance is probably dependent upon whether the motor is moving or not, but it does not have to be. Even if it is dependent upon whether the motor is moving, it will not be possible to predict the form of this dependence without detailed knowledge of the motor.
-a
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