Re: Why tesla coil is air-cored to operate efficiently at high freq?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

On 8 Oct 2005, at 22:43, Tesla list wrote:

> Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
>
>
> It's all about time.  It requires a finite period of time to
> magnetize an iron core, and at high frequencies this time period is
> too long, so RF coils work better without a core.

Some types of sintered powder cores are used in RF inductors
operating well over 20MHz aren't they? I have some small ones here
graded for use up to 30MHz. The real problem with cores is that they
are partially conductive which is not desirable for developing high
voltages over relatively short coil lengths. Having said that, pulse
transformers used in xenon flash units are very compact and develop
up to 6kV open circuit.

  This effect will be
> covered in detail in my forthcoming book, "Tesla's Marvelous
> Transformer:  The Tesla Coil, which I am presently hard at work on.
> It looks like approx 650 pages when I finish it with a lot of
> drawings, figures, and photographs.
>
> I believe the "swinging" action you are referring to is the rapid
> transfer of charge from the capacitor to inductor in a tank circuit.
> Another type of "swinging" transfer occurs between the primary and
> secondary circuits as energy is swapped back and forth.  This is
> indesireable and that's why efficient quenching (turn off) of the
> spark gap is necessary --- to prevent this type of action.  Ideally,
> all energy is transferred to the sec coil in the first burst.  In most
> classic TC oscillators it usually requires 2 to 2.5 pri-sec swaps to
> get all the energy in the sec coil.

I have to question that too. With a suitable coupling constant a SG
coil can transfer all its energy to the secondary (minus gap losses)
in the first primary ringdown.

Malcolm

  Energy is wasted. That's why the
> solid state coils are so much more efficient --- the IGBTs can turn
> off rapidly and trap the energy in the sec coil.
>
> Dr. Resonance
>
>
>
>
>
> >I have three theoretical questions here:
> >
> >
> >I read this from a website: "A normal transformer users an iron core
> >in order to operate at low frequencies, whereas the Tesla Coil is
> >air-cored to operate efficiently at much higher frequencies".
> >
> >
> >
> >I understand that a normal transformer relies on turn ratios and the
> >air core is there to reinforce the magnetic flux.
> >
> >
> >
> >May I then ask, why is an iron core only required in low frequency
> >operation and why do we use an air-core for high frequency operation?
> >
> >
> >Lastly, I read this from another website: " In the Tesla "swing", the
> >kick is supplied by the AC electrical current moving back and forth".
> >Can someone elaborate on this please? Is it actually referring to the
> >LC circuit - both the secondary and primary operating at the same
> >frequency that reinforce each other?
> >
> >
> >
> >Thank you very much for your kind attention.
> >
> >
> >Regards
> >Sam
> >
> >
> >
>
>
>
>