Re: Designing BIG Secondary Coil

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

You can get a variety of large sizes of sonotubes which are a type of
cardboard / waxed tube used for making cement supports.  Just at home depot
today they had up to 6", 8", 10", 12" and 16" forms.  I'm planning on using
a 10" form.  Ed Wingates famous coils typically use these type of tubes for
coilforms so I am told.

Plus they are very inexpensive.  The last time i went to the plumbing
distributor, 12" PVC was almost $100.00 a piece (green stuff).  A 12" four
foot long sonotube is only about $6.00.

Dan




> A suitable form for such large dia secs is always a problem. I think the
PVC
> tubing I've seen at the 12" mark has distressingly large wall thickness,
but
> is this a real world issue? Lexan or Plexi is out of the question for $$
> reasons. Sonotube is known to inflict low Q, though it has been used on
very
> large coils.
>
> I've thought of building a collapsible form, finishing the windings with
> epoxy, collapsing and removing the form, then inserting a modest High-Q
> structure internally for structural support.
>
> There are various tanks, trash buckets, made of HDPE, etc, that could be
> used.
>
>
> Dave Hartwick
>
>
>
>
> Original poster: "Malcolm Watts by way of Terry Fritz
<twftesla-at-qwest-dot-net>"
> <m.j.watts-at-massey.ac.nz>
>
> Hi Dan,
>
> On 5 Sep 2002, at 7:15, Tesla list wrote:
>
> > Original poster: "Mccauley, Daniel H by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>
> >
> >
> >
> > I'm planning on building a relatively large secondary coil and primary
> > set-up which will be the basis for my future (high power 3kVA + ) coils.
> >
> > What should be my primary concerns for a large secondary when i do my
> > design.
> > Right now I have an enormous spool of 20AWG wire and I was planning on
> using
> > an 8" or 12" sonoform as my coilform.
> >
> > What should be my primary concerns for designing something this size.  I
> > guess i want to shoot for a frequency around 100kHz?  (with a proper
> toroid
> > of course)  Aspect ratio of around 4.5 or 5???  Anything else????
> >
> > Thanks
> > Dan
>
> Personally I'd go for the 12" coilform. Re wire size, I have two
> guidelines:
> (1) spacewound coil: the wire should have a minimum diameter of 3
> skin depths (so it could be bigger if you want) at the *lowest*
> frequency of operation (i.e. with the largest terminal you wish to use
> (2) closewound coil: the wire should have a minimum diameter of 5
> skin depths (and preferably more) for the same operating conditions.
>
> Both these guidelines will ensure that the secondary Q is high.
>
> Regards,
> Malcolm
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