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

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: <davep@xxxxxxxx>


> I read this from a website:
   'There are many websites which say many things.'
   8)>>

> "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".
   Whole books have been written covering all the ins and outs of
   this.  Briefly:
     It is easier to design a compact, energy efficient,
     transformer when a 'core' (iron, steel, ferrite,) is
      used, for 'low' freqs, say 25-10KHz.
     The exact upper bound depends on materials, and new ones
     are constantly being created: Tesla had no 'ferrite'
     core materials available.

> I understand that a normal transformer relies on turn ratios and the
> air core
     "air core"?

> is there to reinforce
     The core, when present, _concentrates_ the flux in a smaller
     area for better control of several aspects of the transformer
     design and operation.

> the magnetic flux.

> May I then ask, why is an iron core
    Iron is largely not used, various sorts (there are uncountably
    many...  8)>>) of steels, ferrites, etc...
> only required in low frequency operation
    Losses in the core go up with frequency, more so in some
    materials than others (metals (iron, steel) are lossier/est,
    ferrites less so...
> and why do we use an air-core for high frequency operation?
    To reduce losses.  'most' HF ('radio' uses air cores for this
    reason, tho ferrites work as well, or better, and are also
    widely used.).  Iron/steel cores have higher losses due
    to 'eddy currents' induced int hem, and these go up with
    frequency.

    Also, when a 'Tesla Coil' is used to generate HV, the
    small size allowed by a ferrite core is somewhat irrelavat:
    large sizes are needed to avoid spark over in the wrong
    places.  Similarly, a counducting (steel) core would
    present design problems.

    (Historical note:
     Tesla's original Tesla Coils used various sorts of metallic
     cores.  With the materials available then 'air core' was
     easiest/best to work with....)

> 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?
     It is always iffy 'parseing' someone elses writing.  I would
     interpret this as:
          Any transfromer action requires a change in current.
            (roughly pulsed DC or AC).

          The 'swing' referred to SEEMS to refer to this, and to
          the fact that commonly the Tesla coil is driven by an AC,
          rather than an pulsed DC drive, tho either can be used.

          I would not interpret this as referring to the
          resonance, as such.

     best
      dwp