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 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
> 
> 
> 
> 
> 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
> 
> 
> 
> 
> 
> 
> 
>