The bifilar pancake coil at its resonant frequency

[Magluvin]

Ok. I just had someone ask me about what I have said and I should clear that up.....

When I said there may be an instantaneous mag field when we apply input to the bifi due to neutralizing self inductance as tesla describes, I should have included the resistance that would be part of that RC time in the statement of which would kill the use of the word instantaneous.

But that is not to say that if Tesla is correct that we could not get a much faster charge to the capacitance if the resistance is very low and the self inductance delay of currents were neutralized.  The neutralization of self inductance claim is what we should be looking at as it is the claim.  Im under the strong assumption that the neutralization is in effect when we first introduce dc current to the coil, not at resonance.  If it were at resonance, then we wouldnt have resonance because the self inductance is said to be neutralized due to the capacity magnifying effect of the particular winding scheme. We need L and C for resonance. If one is not there then no ringy dingy. So when is it that the self inductance is neutralized as he claims? It must be at initial input or pulse that Tesla is thinking of.

Thinking deeper, if the claim is true, how does the coils capacitance neutralize the self induction? Does it happen due to charges developing between turns, and those charges affect the self induction between turns? Like some guys here that say it is not flux cutting that causes induction, but it is E field, sooo, where is their beef with that idea???

Like say if the capacitance of the bifi coil or even a regular coil of the same where we had a V meter between every turn, a meter that magically did not affect the circuit in any way, and the coils were 100t and we apply 100v, how long after the input is applied should we see max voltage between each turn pair? Is it instantaineous that every meter would read the same voltage division between each turn? Instantaneous? Or would resistance produce a delay in full charge for each segment vs the time the input was applied? And then further, if the resistance was the only opposition to each turn pair reaching max fraction of the input, and then current begins to flow as self inductance allows, would this not be a no brainer?  Lets say we only read the 2 adjacent turns just in the middle of the coil, when we apply input, will we read 1v between the 2 turns immediately? Or would one say out of the blue that the voltage between those 2 turns wont reach 1v until max current and mag field??? I dont think so.

So the charge in the capacity between turns happens before current is affected by the inductance, and to say there is no current to charge the capacity would be wrong in my opinion, and experience.  Lets say I could wind a coil as we have done with 1uf of capacitance, would current have to flow to charge that capacitance?
If not, then have we charged that capacitance for free and if we disconnect the input at the moment the charge is there, no current happened, then the thing has been energized for free?    Na, Im thinking current flowed till the capacity is fully charged and then the self induction stops further flow and slowly lets current reach peak as we know it from there on..

Thats my story samson simpson.     Think on that.




In a normal coil, there just may be the same effect but it is sooo tiny that if we dont look for it closely we may not notice, as the capacity in the normal coil will have only a tiny fraction of the input applied and further more, the actual capacitance is tiny. But as I said before that tiny capacitance becomes less insignificant when the potential of that same tiny capacity is at a much greater level. So the initial bump that may be there when measuring a normal coil when we first apply dc is most likely tiny as said before and very short lived. But it just might be there. Just a theory based on Teslas claim.  But Im thinking that the bifi will have a bigger more noticeable bump. Im thinking on how to look at that. Would it be a pulse train that the scope will sync to or just a one shot input and can I get my scope to react to the one shot and hold. anyway....


I see the bifi as a series LC for the soul reason of if it were parallel then the cap would accept the input and not through the coil, but a series LC would. And a regular series LC has no way of neutralizing the self inductance. So Tesla says that the coils internal capacitance is responsible for the neutralization of the self inductance.

Mags

[Magluvin]

If we have a 10,000 turn bifilar inductor, it should be pretty high in inductance. It should take longer for current from dc to get to max than most coils we have experienced.

How long would it take when we apply 100v dc for the capacitance to charge to 50v between each turn, based on what criteria would one need to make that determination?

Mags

[Magluvin]

If we have a 10,000 turn bifilar inductor, it should be pretty high in inductance. It should take longer for current from dc to get to max than most coils we have experienced.

How long would it take when we apply 100v dc for the capacitance to charge to 50v between each turn, based on what criteria would one need to make that determination?

Mags

Taking that a bit deeper, if we compared the time it took for the inductor to allow max current from initial input, as to the time it took the capacity to be fully charged to 50v after initial input, could we say that the inductance had any influence on the time it took for the capacity to reach 50v???

Weird to think about aint it?

Mags

[itsu]

In looking at your "TBP coil resonance 1" clip I can see how you have access to the left and right sides of the coil sitting in the CD case with your Hall sensor so you can do the measurement there.  You don't have to scan around the full 360 degrees of the edge of the coil.  The whole thing is symmetrical so there is no need to make more than a single measurement.

I redid my hall sensor measurements, including the edges like mentioned by TK.

Allthough the edges show a minimum negative signal, its all around the coil as far as i could see, so no flipping over.
I used a speaker magnet to compare the results and there we see the same effect that when skimming the magnet/coil
from left to right with the hall sensor at 90° we do see a flip over of the signal on the scope.

Anyway, i think it is all explainable with the field line drawing MH put up earlier.


Video here:  https://www.youtube.com/watch?v=2dxMgjbR90o


Regards Itsu

[itsu]

Another great clip like usual Itsu.  The subject of breaking up a square wave into the sum of a bunch of sine waves at different frequencies is a challenging topic to understand for people with no background in this subject matter.  The short answer is that one of the sine waves in the frequency spectrum of the square wave is at the resonant frequency of the coil, and it's only that particular frequency that makes the coil resonate.

And that is why when you are looking for resonance or just to see how a circuit responds to a frequency sweep, you never use a square wave.  Multiple different square wave frequencies will make an LC resonator like the TBP coil resonate at its resonant frequency.  That can cause errors where you think the "wrong" square wave frequency is telling you the resonant frequency of the device under test.

I agree, its a challenging topic, that like you said has to do with the fact that a square wave is made up of all kind of sine waves and will generate odd harmonics.

Itsu