RE: Designing BIG Secondary Coil

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

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.

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
>
>
>
>
>
>
>