Back EMF vs. Collapsing Magnetic Field Spike

[nilrehob]

"The EMF induced in an electric circuit always acts in such a direction that the current it drives around a closed circuit produces a magnetic field which opposes the change in magnetic flux."
“The induced electromotive force or EMF in any closed circuit is equal to the time rate of change of the magnetic flux through the circuit.”

What about open circuits?

[Aaron]

inductive spike

Back EMF is the same as Counter EMF and in either case, including Forward EMF, none of these are the inductive spike from a coil.

If he is saying in the book that forward emf is the inductive spike then he is misusing the entire concept of force as in electromotive force. Is there force with zero work or pure potential moving through a coil and out of it? It might sound good but is is like an oxymoron...kind of like "military intelligence."

I have the same book from a friend it is a great reference nevertheless.

[nilrehob]

Back EMF is the same as Counter EMF and in either case, including Forward EMF, none of these are the inductive spike from a coil.

If he is saying in the book that forward emf is the inductive spike then he is misusing the entire concept of force as in electromotive force. Is there force with zero work or pure potential moving through a coil and out of it? It might sound good but is is like an oxymoron...kind of like "military intelligence."

I have the same book from a friend it is a great reference nevertheless.

Please forgive me for being a skeptic enthusiast trying to keep both feet on the ground.
I have built two Bedini SSG's and I'm currently doing a few experiments on the Tesla switch and read and watch as much as I can about this.
I'm not saying that You or anyone else is right or wrong, as I actually don't know.
But could You, when You have the time, point out where in the book (2nd ed) You think Paul Scherz is wrong, and also how he is wrong? (maybe around pages 124-126, 140, 142-147) I would really appreciate it.

[Aaron]

spike not current

* 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.

[nilrehob]

I just did a test using components that I had lying around: coil ~166mH, cap 47uF, diode 1N4007, bat 12V and a switch.
The amp draw of the coil was ~500mA.
Battery, coil and switch in series.
Coil, diode and cap in series.
Switching on/off a few times the cap easily reached 80V.
Doing this repeatedly and emptying the cap each time it reached around 80V I took the average of the changes in voltage for each on/off-cycle squared and got ~550V^2. (Edit: max change squared = 688V^2)
The energy in each forward EMF spike captured by the cap would then be about (47*10^-6*550)/2=0.013 J. (Edit: max energy = 0.016 J)
The energy in the coil before switched off would be near (166*10^-3*0.5^2)/2=0.021 J
The difference in energy I blame resistance and other losses and me calculating the inductance wrong (using supposed length of the wire and the physical dimension of the coil).

What is wrong with my assumptions in this exercise?

[Sephiroth]

I'm going to step in to confuse matters a bit more

I personally think both Aaron and nilrehob are correct

but the output of bedini's circuits contains two componants and neither of them is back-emf as aaron has already mentioned.

but the transient spike is only part of the output.

when current has been cut off from the coil, then immeadiatly upon the opening of the switch we get the transient spike that can shoot off the top of our oscilloscopes. But following this transient event is the flyback current which I think could be described as forward emf as it is generated by the collapsing field in a similar way as current is generated when you pull a magnet off the top of the core.

The flyback current is recycling the energy we put into the system but the transient spike is the part that allows us to gain more energy in our systems.

My two cents

[nilrehob]

I have just found the "Radiant Energy"-thread so I have to chew on this for a while.
But I'm still *very* skeptic!

[nilrehob]

Please forgive me, but I still can't see the forward EMF spike as anything else than the energy in the coil desperately trying to find another form as quick as possible, and as there are high resistance in the way You get high voltage and low current.

The spike has a width, and a current, albeit very small, just enough to make the spike carry the energy that was previously in the coil.

If the capacitor in the circuit in my previous post has a voltage higher than the battery, the energy in the coil compresses itself even more to an even higher (but thinner) spike to make its way into the capacitor. The only other alternative is to convert itself to heat.

I just tested a Bedini SSG charging a capacitor instead of a battery, and it shows very clearly that the spike grows in height as the capacitor collects more and more energy.

This again leads me to the conclusion that the driving battery connected to a coil should be connected as short as possible, just to "fill up" the coil, as any current flowing in the coil after the coil is "full" cannot be recollected.

I'm only looking at a single spike here, as a single event. A train of spikes may add to the story, but I'm not there yet.

Please correct me anyone if You think I'm wrong about the spikes, and a simple easy to replicate setup to show it would be really helpful.

I'm sure there are things in "Tesla tech" (and others) than cannot be described in current theories and formulas, but I'm sure a spike in this context is easy to explain using common textbooks.

[nilrehob]

I'm going to step in to confuse matters a bit more

The Bedini SSG has more components in it than my simple test above and thus I think it works somewhat differently. The passing magnet, for example, I'm sure adds to the equation.

I think I have heard Bedini say something like "the magnet sucks out the field" as it passes away from the coil. Maybe that is how energy is added in the mechanical SSG.
The SS SSG doesnt have the magnet but may work differently as it has a higher frequency (just a guess as I haven't built a SS SSG yet).
Would a SSG with no wheel, magnets or transistor work with a relay (instead of the transistor) switching in low freq? My guess is it won't, not even if You trim the width of the puls to match the size of the coil.

Wouldn't it be appropriate to try to separate the different mechanisms in the Bedini SSG so that we *really* understand what is happening?

[boguslaw]

I was thinking about this...

There is a magic in iron core. Magnetic field (or rather current) inside iron propagates quite slowly, there is a delay from first time when magnetic field touch core and to the point of "filling" all iron core. The same is for diminishing magnetic field.

Now if you have a coil with iron core and magnet attached to it so magnetic field is strengthen by permanent magnet field , nothing changes for coil operations because MAGNETIC FLUX CHANGE is source of current flow, not simply static magnetic field.

Thing are going to start interesting IF we have a nice way to QUICKLY remove permanent magnetic field exactly at the point when coil magnetic field is starting to collapse because of turn off of power source.Iron core is still magnetized but there is no external source of static magnetic field - so magnetic field of coil + magnetic field of iron core COLLAPSE.

You see how SSG is using permanent magnet and iron core to extract energy from static magnetic field.


How do you think about it ?

[Jetijs]

If you want inductive spikes without any magnets involved, look at Bedini self oscillator circuits or Peters rotary attraction motor.

[Sephiroth]

nilrehob - I am almost 100% confident that the passing magnets actually take energy away energy from electrical output and does not add to it.

Also, what you are saying in your previous post is correct that as the capactior charges the flyback increases in voltage and reduces in duration BUT remember that what you are calling the spike is actually the flyback current I mentioned and is not the transient spike that aaron is refering to. The transient spike preceeds the flyback.

[Aaron]

spike

The spike has a width, and a current, albeit very small, just enough to make the spike carry the energy that was previously in the coil.

Right, if you zoom into the spike close enough, you will see it is a triangle with some width getting wider towards the bottom. However, there are spikes like this but also true impulses without the current...this is firmly established.

[Aaron]

current after disconnect

There is a way to have current in the coil AFTER
you remove the input power.

[boguslaw]

Aaron,

Great ! Now teach us how to circulate such current in closed path and extract energy from such generator !