The bifilar pancake coil at its resonant frequency

[tinman]

Brad: Your wirewound cement resistor probably has significant inductance too!

Ah yes
Will replace that with a carbon one tomorrow,and retry.


Brad

[MileHigh]

But you "made" it look way way worse than the actual outcome. Way worse. If you made that mistake working at a law firm you would be fired. By making it look that bad why would anyone in their right mind even try for themselves once they innocently take in your concocted results as 'fact', that are sooo far of it isnt even funny anymore.

I am not the bogeyman so stop the demonizing right now.  I gave you my explanation and you are not going to ignore it.  I did not "concoct" anything, period.

Here is your takeaway:  It looks like with any bifilar coil that you work with on your bench, to sustain a very small amount of energy in the resonant cavity, you have to continuously burn off a very large amount of power in the wire resistance relative to the resonant cavity energy.

Now, that is likely to be true for anybody's bifilar coil, period.

[gyulasun]

Also let's use Conrad's numbers again to look at the series bifilar coil a different way:

34 microhenries, 49 picofarads of self-capacitance

Let's just say that a reasonable peak-to-peak voltage for the self-resonating coil is 400 volts.

So the capacitive energy is 0.98 microjoules.

You calculated 0.98 uJ (microjoule) capacitive energy in a 49 pF capacitor when this cap has 400 V across it
as you defined in your example.

My calculation gives 3.92 uJ (microjoule). 

Now, I am going to make an apples and oranges comparison here.  Let's assume the inductor
is pulsed at a low duty cycle in some kind of pulse circuit such that the average power dissipation from
the 10-ohm coil is low and not an issue, and the peak current through the coil is 400 milliamperes.

So the inductive energy is 2.72 mircojoules.

Well, in this apples and oranges comparison, the two energy levels are pretty comparable and it certainly
doesn't look like a gnat sitting on the back of an elephant.  However, there is one caveat. 
If the coil is functioning in some kind of pulse circuit the self-capacitance is not really there, there is
no real self-resonance taking place. 

I think you mean pulsing a bifilar coil at a low enough frequency well away from its self-resonant
frequency, right? If yes, then this mode of operation is not comparable to the circumstances
defined in Tesla's patent.   

And there is no sense to compare 2.72 uJ energy in the coil to 0.98 uJ energy in the capacitor (this latter
energy is 3.92 uJ by my calculation), albeit this certainly fits to your apples to oranges comparison.

By the way, is there any sense for making such apple-orange comparisons?

This question arises because in your next text you introduce another example where the self-resonance
voltage across a coil is 40 Vpp and then you compare this 0.0098 uJ energy to another coil pulsed with
a low duty cycle 400 mA peak current that creates 2.72 uJ energy... 

Finally, one last kick at the napkin.
If the self-resonance is say 40 volts peak-to-peak, then the energy stored in the self-capacitance
is 0.0098 microjoules.  And the energy in the coll at 400 milliamperes is 2.72 microjoules.
In this apples and oranges comparison the inductive energy is 277 times the capacitive energy. 

It is okay that you can compare apples to oranges as you wish but such comparisons are good fun
for some people but surely not scientific at all.

I am not nit-picking with you, no offense intended at all, simply trying to find sense in some of your posts
and / or trying to correct mistakes other readers here may not recognise and from your posts they may remain
with the bad impression: a bifilar coil as per the Tesla patent is good for nothing.
And no, I will not answer your would-be next question: what is the advantage of using a bifilar coil...  lol

Gyula

[Grumage]

 

[Magluvin]

You are missing the key point here.  Tesla states in the patent that at the right AC excitation frequency the bifilar coil (or any coil) will appear as a pure resistance.  This is where the coil is modeled as a series LC circuit.  And we know that when you excite a series LC circuit with a pure sine wave that the series LC circuit looks like the wire resistance only because at the right AC excitation frequency the reactance of the inductance and the capacitance cancel each other out.

So if you pulse a bifilar coil, this is not the same as pure sine wave excitation at the resonant frequency, and the "wire resistance only" statement does not apply.

He doesnt 'state' exactly what you quote in bold.  anyway....

Ok, so if it has to be the right freq, then what happens when we apply a dc input, pulse long, short, indefinitely on, what will happen when the current is applied? Is the coil not going to take the easy way upward in current at its resonant freq?  If the pulse were very short, AND he claims that the inductance is "neutralized" due to the capacitance mod, Why would the inductance at resonance be neutralized, but a pulse of dc cause the coil not to follow the upward 1/4 cycle of its resonant freq?

He does state that the the coil secures a capacity sufficient enough to neutralize the self induction. So it sounds to me like the capacity is sufficient enough to ignore the inductance with a pulse.

Its like this... If his claim is that the capacitance change, due to only the differential voltage difference in adjacent turns vs a normal winding, neutralizes the inductance, why would we be concerned that the inductance is neutralized only if it were driven by a particular freq? Like I get what you are saying, but what is the point of bringing up the neutralization due to the capacitance mod of a series bifi if it didnt mean anything and really doesnt need to be said? Resonance wasnt a new idea and was well known how to achieve it. He isnt making the claim on a resonance basis that had been understood for some time, as if it were new and he is describing the process of what happens to the inductance at only a particular freq. The claim is that the change in capacitance differential voltage due to the bifi winding vs normal causes the inductance to be neutralized. That is the claim. His 'claims are always at the bottom of the descriptions. 

We cannot compare this to a coil in parallel to an outside capacitance. Adding a capacitor as in a typical lc, a pulsed input would be mostly ignored by the coil and the cap would take on the pulse. And how fast does that cap take that pulse? Pretty darn fast. But that does nothing for the coil when considering we are looking for the possibility of a current 'through the coil' when the pulse is applied, not to just initially to an added cap of an LC.  And Im thinking he is saying what I have been explaining here. will see.

Mags



This is the claim of which is usually put after the description, and in a few different ways of saying it to cover his ass.. That is the claim Im referring to.



" A coil for electric apparatus the adjacent convolutions of which form parts of the circuit between which there exists a potential difference sufficient to secure in the coil a capacity capable of neutralizing its self-induction, as hereinbefore described."