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



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. 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. 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