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Re: secondary core other than air



Tesla list wrote:
> 
> Original poster: "Steve" <Steve-at-g8cyerichmond.freeserve.co.uk>
> 
> This is a point I have often wondered about. Ferrites are used at very much
> higher frequencies than Tesla coils generally operate at. In fact I have a
> ferrite antenna from a paging receiver that was used at 156MHz!!! Think of
> the ferrite antennas (loopsticks) used in bc receivers, they are ok at up to
> about 3MHz. In fact I have used the last mentioned rods as the core of
> transformers handling up to 50W without any trouble.
> ----- Original Message -----
> From: Tesla list <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Monday, August 07, 2000 6:38 PM
> Subject: Re: secondary core other than air
> 
> > Original poster: "Garry F." <garryfre-at-pacbell-dot-net>
> >
> > I often thought the reason telsa coils were air core was because Ferrite
> > might not be capable of rapid magnetic change that would be required for a
> > high frequency app such as tesla coils. I think the atoms would not be
> able
> > to spring back into their original orientation once the magentic field
> > collapes fast enough.
> >
> > I could be wrong tho, but I tend to think this is why they reccommend only
> > non-magnetic wire as conductors in Tesla coils
> >
> > ----- Original Message -----
> > From: "Tesla list" <tesla-at-pupman-dot-com>
> > To: <tesla-at-pupman-dot-com>
> > Sent: Sunday, August 06, 2000 2:04 PM
> > Subject: Re: secondary core other than air
> >
> >
> > > Original poster: Terry Fritz <twftesla-at-uswest-dot-net>
> > >
> > > Hi Garth,
> > >
> > >         #21 enameled magnet wire is about 33.1 turns per inch.  So you
> > probably
> > > have #21 which is fine.
> > >
> > >         Don't worry about only 5 turns on the primary.  Just tune your
> > coil
> > > with
> > > what you have and all should work fine.
> > >
> > >         I don't know of any way of lowering the secondary frequency
> short
> > of a
> > > bigger or more top load.  Ferrites in or around the secondary are not
> > > impossible, but that would take a lot of thought and design.  Perhaps a
> > fun
> > > project but too messy in this case.  Just tune with what you have and
> all
> > will
> > > be well.
> > >
> > > Cheers,
> > >
> > >         Terry
> > >
> > >
> > > At 03:09 PM 8/6/00 +0200, you wrote:
> > > >
> > > > Would it be possible to use something other than an air core to
> increase
> > the
> > > > secondary inductance and Q factor?
> > > >
> > > > Are their any possible cores available?  I know something like ferrite
> > core
> > > > would create internal arcs, but surely there must be something out
> > there!
> > > >
> > > > I have just wound my 6.4" secondary with what I was told to be #24
> wire,
> > but
> > > > wintesla seems to use incorrect figures for wire guage and turns per
> > inch.
> > > > My secondary has 33 turns/inch.
> > > >
> > > > My secondary inductance is way too low and I now have re-calculated my
> > > > primary with only 5 turns which I think will be terrible for spark gap
> > > > losses.  My topload is 20" wide so I can't drop secondary resonance
> any
> > more
> > > > unless I use some secondary core other than air or wind more turns on
> > the
> > > > secondary.

	There are many different formulations of ferrite materials, usable from
below 60 Hz to well into the upper microwave region.  The AMIDON site:

	http://www.bytemark-dot-com/amidon/content0.htm

has a lot of good information on ferrite cores and also the materials
themselves.  They address both power and "linear" applications.  There
is also information on how to calculate the flux density in a given core
at a given frequency at a given number of turns/volt.  Strongly
recommend it to all who may bee thinking of using ferrite cores.

Ed