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02-25-2009, 10:56 AM
 Aaron Co-Founder & Moderator Join Date: Feb 2007 Location: Washington State Posts: 10,946
spike not current

Quote:
 Originally Posted by nilrehob * forward EMF appears when the magnetic field in a coil collapses and generates a current in the same direction as the interrupted current
EMF isn't really a force according to the experts. I say there isn't much force to the spike and there isn't.

Do you realize you're claiming (or the man in the book) there is a net gain in forward current.

Here is the chronology of what happens according to that claim.

1. There is applied power and this would technically be a Forward EMF.
2. Back EMF or back current opposes the forward current.
3. The current was interrupted (the applied/forward current is interrupted)
4. now there is a generation of current that goes in the same direction as the original forward current that was interrupted according to what you've posted.

You're saying that there are two emfs to begin with...forward and backward in opposition....coil is turned off and you wind up with a net gain of a forward current going in the same direction as the original interrupted forward current.

That means when the power on a coil is turned off, you wind up with a forward current or amperage. If that is true, then there is a magnetic field being maintained preventing a collapse. As there would be current in the coil going in the direction necessary to make the magnetic field to begin with.

The reality of what we actually do wind up with when the coil collapses is a high voltage spike with virtually no current at all - that is the whole point to calling it a spike..a spike means there is no pulse width to it and with no pulse width there isn't a time variable to speak of meaning if there is no time to speak of per spike, there isn't current flowing. That is why it is called voltage potential.

When the coil collapses, voltage goes through the roof while current goes through the floor.
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Sincerely,
Aaron Murakami