Tesla's "COIL FOR ELECTRO-MAGNETS".

[gyulasun]

Hi Conrad,

When I have some more time this weekend I may add some more comments, now I notice only the eddy current losses of the steel bolt, influencing even the measurements you do when using the LCR meter but the thing is that several experimenters when doing the so called delayed Lenz effect tests often use bolts as a core, so you can test it too, of course.
Nevertheless, I advise to have at hand a normal ferrite rod piece too (OD=6mm length=40mm) from RS components (link: http://at.rs-online.com/web/p/ferrit-stabkern/4674065/ )  with one such core eddy losses will be negligibly small even at 10 kHz or higher.
Your link to the multilayer-multiturn coil calculator is okay and I would like to refer to another one I have recently found a bit more flexible and precise, works also on-line but freely downloadable too and have some additional plug-in softwares to make it more versatile (I have no any business interest with its creator  ),  see here: http://coil32.narod.ru/calc/multi_layer-en.html  and download it here, the plug-ins are also here: http://coil32.narod.ru/download-en.html

Regarding the drop in inductance at the 10 kHz LCR meter's measuring frequency for the air core series bifilar, I think the high value self capacitance of this multiturn bifilar coil causes it, see below the explanation. You may have also noticed that the air core bifilar has a bit higher inductance at 1 kHz (176 mH) than at 100 Hz (168 mH), this is because the 1 kHz is closer to the 4.6 kHz self resonant frequency, here I assume this latter frequency is the first parallel resonant frequency of the series bifilar coil caused by the about 170 mH inductance and the self capacitance.

The interesting thing is that such bifilar coils (connected as series bifilar like it is now) do have multiple resonances as the frequency increases, what is more: parallel and series resonances should alternate each other as you sweep the frequency due to the distributed nature of the self capacitance and inductance.
Here is a good site (watchable only via the internet wayback machine since last December)  on some measurements where the series bifilar coil is made of a coaxial cable and in Figure 10 the magnitude of the impedance is shown in the function of the frequency (the high impedance peaks are the parallel and the low impedance valleys are the series resonance points:  https://web.archive.org/web/20130321175122/http://vk1od.net/antenna/coaxtrap/index.htm 

When you have some more time next week, you may wish to check your multiturn bifilar coil in a measuring circuit and experience (by sweeping through the frequencies) the impedance peaks or the valleys manifested by the changing voltage values across the series bifilar, driving it from your function generator. (A good measuring circuit is to be figured out for that.)

Of course a coaxial cable is a transmission line where the outer conductor encircles the inner conductor and these two are inherently guided in parallel with each other of course. When you make a bifilar coil, the two pieces of wires can also be considered as a (long) transmission line where they are guided next to each other in parallel too (though quite often these are twisted to increase the capacitance between them).
Now you or MileHigh can understand why the inductance for the air core series bifilar is so small at 10 kHz: at this frequency the impedance is surely near to a series resonant point (near to an impedance valley) but it is still inductive. At a series resonant frequency (especially at the first series frequency just after the first parallel one) the impedance is nearly the DC resistance of the two series coils (plus some dielectric losses of the enamel and bobbin or core losses when you use any ferromagnetic core etc).

Greetings,  Gyula

[Farmhand]

OK something that has been touched on before but another advantage as compared to tuning a coil with an external capacitor is that with an external capacitor the cpacitance is at the end of the coil leads or terminals and so any current going to the capacitor must flow through the coil and it's DC resistance. Not so with the bifilar coil, there would be little to nil tank current flowing through the DC resistance of the coil, seems like.
Which must improve efficiency surely. I set up an isolation transformer with the coils wound on different parts of the big core last night and tuned the output coil with a 14 uf capacitor for 50 Hz, when I ran the setup the voltage at the output coil was more than the input coil, almost double, same turn count (inductances trimmed). But the input required was more.
The way I see it it is the current in the output coil "tank" for want of a better word causing more losses, if there was no capacitor there but the coil was a bifilar and was "specifically wound as Tesla describes" but instead for 50 Hz "resonance" as I did with the 14 uF capacitor the losses would be much less. The losses are proportionate to the voltage applied and the current induced in the "tank" through the resistance. Distributed capacitance would negate all that tank current and loss I think.

So tuning with a external capacitor is not the same as using a Coil For Electro-Magnets made to order for the same purpose, in that way at least and it's a big thing as I see it.

This is something we can test with the high resistance coils like Mags is making. 

So one for the trained or self educated guys, with the capacitance evenly distributed how much resistive loss is involved in a coil with it's own evenly distributed tank capacitor as compared to a comparative coil (same inductance) but tuned with an external capacitor ? Same or different ?

When I first added the cap I figured it would increase the input of course as the activity is increased, but then I thought if that was a bifilar coil no cap would be needed across the coil and so no current would be flowing through the end of the coil with no load.

Capacity secured in this particular way possesses an additional advantage in that it is evenly distributed, a consideration of the greatest importance in many cases, and the results, both as to-efficiency and economy, are the more readily and easily obtained as the size of the coils, the potential difference, or frequency of the currents are increased.

..

P.S. On a side note it irks me to no end when people like Utkin when referring to this coil make statements like "No wonder Tesla always said this coil was an energy amplifying coil." I doubt he said that, I see no evidence of it.

In my opinion we should go through his claims and pick them to pieces. He just adds so much BS it make a joke out of Tesla's work. But people lap it up and re link it and promote the rubbish. I doubt very much Tesla ever uttered those words in relation to this coil or any other. But if he did ther ought to be record of it if people are saying he always used to say it. What a crock.

When I see Utkin or someone else make such a statement I immediately think, crackpot.

..

[Farmhand]

So to better explain what I'm envisioning, with a regular coil and tuning capacitor when the applied voltage declines and therefore the magnetic field declines to maintain the current, that current keeps flowing through the wire and it's resistance to the ends of the coils wire before it gets to the capacitor. But with the bifilar coil there is no capacitor at the ends of the coil. So what happens to the current ? My guess is the coils distributed capacitance takes current from along the entire length of the coils wire via the dielectric medium being the insulation on the wire. Just a guess that if so, the ESR of this capacitor is very good.

Any thoughts.     

P.S. As an example just say I had a coil of both kinds which has about 720 mH and about 22 Ohms DC resistance with 220 nF excited at 400 Hz.

A generator capable of 400 Hz and about 220 volts would be nice to experiment with. I wonder what the frequency of a car alternator would be at 1200 RPM, I'll have to check.
I could bypass the rectifier and use one phase of that maybe for a lower voltage. 

..

[Magluvin]

OK something that has been touched on before but another advantage as compared to tuning a coil with an external capacitor is that with an external capacitor the cpacitance is at the end of the coil leads or terminals and so any current going to the capacitor must flow through the coil and it's DC resistance. Not so with the bifilar coil, there would be little to nil tank current flowing through the DC resistance of the coil, seems like.
Which must improve efficiency surely. I set up an isolation transformer with the coils wound on different parts of the big core last night and tuned the output coil with a 14 uf capacitor for 50 Hz, when I ran the setup the voltage at the output coil was more than the input coil, almost double, same turn count (inductances trimmed). But the input required was more.
The way I see it it is the current in the output coil "tank" for want of a better word causing more losses, if there was no capacitor there but the coil was a bifilar and was "specifically wound as Tesla describes" but instead for 50 Hz "resonance" as I did with the 14 uF capacitor the losses would be much less. The losses are proportionate to the voltage applied and the current induced in the "tank" through the resistance. Distributed capacitance would negate all that tank current and loss I think.

So tuning with a external capacitor is not the same as using a Coil For Electro-Magnets made to order for the same purpose, in that way at least and it's a big thing as I see it.

This is something we can test with the high resistance coils like Mags is making. 

So one for the trained or self educated guys, with the capacitance evenly distributed how much resistive loss is involved in a coil with it's own evenly distributed tank capacitor as compared to a comparative coil (same inductance) but tuned with an external capacitor ? Same or different ?

When I first added the cap I figured it would increase the input of course as the activity is increased, but then I thought if that was a bifilar coil no cap would be needed across the coil and so no current would be flowing through the end of the coil with no load.


..

P.S. On a side note it irks me to no end when people like Utkin when referring to this coil make statements like "No wonder Tesla always said this coil was an energy amplifying coil." I doubt he said that, I see no evidence of it.

In my opinion we should go through his claims and pick them to pieces. He just adds so much BS it make a joke out of Tesla's work. But people lap it up and re link it and promote the rubbish. I doubt very much Tesla ever uttered those words in relation to this coil or any other. But if he did ther ought to be record of it if people are saying he always used to say it. What a crock.

When I see Utkin or someone else make such a statement I immediately think, crackpot.

..

"So tuning with a external capacitor is not the same as using a Coil For Electro-Magnets made to order for the same purpose, in that way at least and it's a big thing as I see it."

Yep, I believe it is different.    A normal coil with a cap in parallel, if we were to apply dc or say initial input, the cap is right there across the supply and takes on current immediately. So will the bifi coil. But the difference is, to charge the bifi cap, the charge has to go through the coil, but the typical LC this is not the case. They are not exactly the same.

Ill have time to set up to wind that coil tomorrow evening.  The bobbins that Im using for twin spools to wind a single are going to need a free spinning place to reel off of. The wire is very thin and have learned to be careful. The bobbins are door panel clips with the lil christmas tree tips. No through hole. So I have some hobby bearings Ill temporarily mount on a base. The bobbins also have different amounts of wire depending on where they broke while winding them originally, so they have to be able to spin independently. But now I have good use for that wire.

Im going to remove 3 coils(possibly more if need be) from the motor and use the one space in the middle for testing the 2 different coils so the motor coils dont interfere too much. They are all really close, bout 1mm spacing. The bifi will have a 4 pin terminal for trying different configurations.

Mags

[MileHigh]

Farmhand:

You are right about the current being lower for a self-resonating coil but your reasoning is incorrect.  The current is lower because the amount of energy stored in the self-resonating coil is lower, whether that be monofiler or series bifilar.

But firstly and formostly, you are forgetting the basics.  The current flow in the coil is synonymous with the energy stored in the coil, period.  You simply have to have current flow and deal with the associated i-squared-r losses no matter what.  There is no possible bypass or work-around for the current flow in a self-resonating coil, because the coil stores the energy in the current flow itself.

But here is a simple thought experiment:  If you have a regular capacitor in the LC circuit and start to decrease the value of the capacitor, the frequency goes up.  What is mentioned less often but is also true is that the AC voltage has to increase while the capacitor decreases in size.  If you read 10 volts AC when the cap is 100 uF, and you assume that the resonator energy remains constant, what is the AC voltage when the capacitance is only 37 pF?

The self-resonating coil with no capacitance would have to resonate at some crazy high voltage.  The voltage would be so high that the air would break down and the energy would be nearly instantly drained out of the coil.  And that's what happens all the time in real life.  If you connect a coil across a 1.5 volt battery, when you go to disconnect, the the coil discharges through a spark gap.  The spark gap may be so tiny that you don't hear it or see it but it is still there.

So, it's essentially impossible to have a self-resonating coil store a lot of energy because it "shorts itself out" the moment you go to disconnect from the battery.  Unless you are in a vacuum or do some experiments with coils submerged in insulating oil, a self-resonating coil in air will always be a low energy affair compared to the same coil connected to a capacitor.

MileHigh