RE: Designing BIG Secondary Coil

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

HI Dave,

On 6 Sep 2002, at 21:00, Tesla list wrote:

> Original poster: "Dave Hartwick by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>
> 
> Dr.,
> I was probably incorrectly assuming that space winding improves performance
> because of reduced inter-turn capacitance. I've never experienced inter-turn
> insulation breakdown, though I know it occurs.

Space winding doesn't affect the total capacitance of the coil much 
at all. What it does affect is the proximity effect. The result is 
that you can wind a coil to have the same inductance with far less 
copper mass which performs as well if not better than one closewound 
with thick wire. Cheaper and lighter.

Regards,
malcolm

> Regarding secondary dimensions: I've got 7 puny feet of vertical space to
> work with in the basement. I think I'm stuck there--wife and neighbor
> factors. So I was thinking about 12 or more inch dia form, but not more than
> about 24" tall. 2:1 aspect ratio or less. The topload will have to be
> elevated somewhat.
> 
> With a 5" x 28" toroid, my current 4" x 24" sec (1500 turns close wound)
> resonates at 140 kHZ. I'm thinking that a big fat secondary of the same
> height with thicker wire  would lower Fo, raise Q, and thus be a superior
> performer. I just bought a big Polyprop trash can that will do the trick at
> my favorite coiling center--Walmart.
> Dave
> 
> 
> 
> 
> Original poster: "D.C. Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <resonance-at-jvlnet-dot-com>
> 
> 
> 
> Dave:
> 
> If your sec. toroid is suitably large why bother with space winding.  The
> toroid will protect a properly tuned coil.
> 
> Would suggest 18 to 24 in dia with a 4.5:1 height to dia. ratio.  36 x 8 in
> toroid or 48 x 12 in toroid made inexpensively from McMaster-Carr flex-lock
> aluminum duct hose, p/n 55335K for the 12 in. dia.and 55335K26 for the 8 in.
> dia x 25 ft length ---both under $20.  Have a local "real good" local welder
> weld the ends together and also weld a support cross brace.  Cover with
> strips of Al tape from Home Depot and you're ready to roll.
> 
> Dr. Resonance
> 
> 
> 
> 
> ----- Original Message -----
> From: "Tesla list" <tesla-at-pupman-dot-com>
> To: <tesla-at-pupman-dot-com>
> Sent: Friday, September 06, 2002 3:11 PM
> Subject: RE: Designing BIG Secondary Coil
> 
> 
> > Original poster: "Dave Hartwick by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>
> >
> > Malcom,
> > What is the composition of that sewer pipe? You're not talking about terra
> > cotta pipe, I assume?
> >
> > How are you accomplishing space winding?
> > Dave H
> >
> >
> >
> > Original poster: "Malcolm Watts by way of Terry Fritz
> <twftesla-at-qwest-dot-net>"
> > <m.j.watts-at-massey.ac.nz>
> >
> > Hi Dave,
> >
> > On 5 Sep 2002, at 19:28, Tesla list wrote:
> >
> > > Original poster: "Dave Hartwick by way of Terry Fritz
> > <twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>
> > >
> > > Malcom,
> > > Fascinating recommendations. With a confined Lab, I've been thinking
> small
> > > dia secondaries, but this really makes no sense. The vertical height is
> > the
> > > problem. Why not go with large diameters?
> > > Of course, there is a minimum vertical height limitation, lest excessive
> > > striking of the strike rail become a problem.
> > >
> > > 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.
> >
> > Re the wall thickness: the best secondary I have wound to date
> > followed the guidelines for a spacewound coil and was wound on -
> > gasp!- a 10" diameter piece of thickwall sewer pipe. It outperforms a
> > closewound coil wound on a skeletal former wrapped with 1/8" thick
> > HDPE sheet with a 17" diameter and closewound with wire that *didn't*
> > meet the closewound guideline.
> >     I met with complete failure winding a 12" coil onto sonotube, and
> > that was with the tarred layer removed and the remains for the form
> > varnished *and not pre-dried* :(  The measure unloaded Q of that
> > coil, spacewound and all was a miserable 30 - 40. That coil went out
> > in an annual solid waste collection.
> >     The unloaded Q of the 10" sewer pipe coil (not pre-varnished BTW)
> > was about 300.
> >
> > Regards,
> > Malcolm
> >
> > > 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
> >
> >
> >
> >
> >
> >
> >
> 
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