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03-01-2009, 08:20 PM
 Aaron Co-Founder & Moderator Join Date: Feb 2007 Location: Washington State Posts: 10,845
What is Back EMF

This is an old scope shot from my 2000 turn trifilar Bedini oscillator.

The little stubs at the bottom are about 13 volts input....BACK EMF is occurring DURING the input portion of those little stubs. Again - the BACK EMF is occurring during those little stubs at the bottom WHILE 13 volts is being applied to the coil. Lenz Law is taking place DURING the application of 13 volts - that is where the Back EMF is.

See the tall spikes? That is hundreds of volts potential and it is those spikes that you want and those spikes have NOTHING to do with Back EMF and is NOT Forward EMF.

The most efficient coil arrangement to get the transfer of this if using a secondary is a 1:1 turn ratio. It is not a turns ratio setup for stepping up voltage, it is a time rate of change setup.

Anyone needing further clarification on what Back EMF is, please read this:

Definitions of Back EMF
What is the common theme here? A counter current that opposes the applied field. The applied field, the normal flow of current, the applied voltage - these are all things that Back EMF are opposing....and it is all of these things that are NOT the spike. The spike is NOT the applied field, it is NOT the normal flow of current, it is NOT the applied Voltage and it is most definitely NOT the counter current that opposes these things that are also not what the spike are.

What law describes this action?
Lenz's Law

In 1834, Russian physicist Heinrich Lenz discovered the directional relationships between induced magnetic fields, voltage, and current when a conductor is passed within the lines of force of a magnetic field. Lenz's law states:

"An induced electromotive force generates a current that induces a counter magnetic field that opposes the magnetic field generating the current."

The FACT that the spike is not back emf has been firmly established in all basic electromagnetics for many, many, many years. It is also not a forward EMF.

Current can be maintained in a coil after power is disconnected but any of the above is not it.
__________________
Sincerely,
Aaron Murakami