Re: Flat secondary measurements

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

John Tomacic wrote:
> I used "Wintesla" to calculate the inductance of my 5.625 inch
> diameter coil, 21.9 inches long wound with #24 wire. It gives an
> inductance of 32.64 mH, and length of wire 1478.55 feet.

> For the flat spiral I used the following formula for inductance:
> L= (NR)^2/(8R+11W) N= 431 turns, R=6.55 (inside radius = 2 in,
> outside radius = 11.1 inches) and W= 9.1 in (431 turns * 0.0211
> (wire dia)).

John, that's brilliant!  With acmi, I get

flat {
   radius1 2"  
   radius2 11.1"
   height 0
   conductor 24 awg 
   turns 431
}

helix {
   radius 5.625/2"
   height1 0
   height2 21.9"
   conductor 24 awg 
   turns 1004
}

      Flat      Helix
L   52.8mH      33.0mH
R   38.51 ohm   38.52 ohm

That's amazing - I never would have guessed that.  Some real food for
thought there. Gives me an idea...

Inductance Contest
------------------
You have 426.72 metres (1400 feet) of 24 awg (0.51055mm diam) wire.

What's the highest inductance you can achieve with it?

Coils must be single layer, with concentric windings.  The minimum
allowable pitch is 0.6382 mm (0.025125 inches) which corresponds to
a spacing ratio of 0.8.

Answers direct.

Terry wrote:
> I guess Paul is working on acmi and TSSP. 

tssp yes, but acmi can already do all of these, any old weird shape,
so long as all the turns are concentric.  You can put in as many
windings as you like, too.

> Oops!!  The secondary voltage profile will not work...

Guess it for now. You should get within 10% on fres.  We'll extract
some nominal voltage profiles from tssp in due coarse.

I'm baffled by the palaver over spiral wire length! 

Peter, I like your option (a).  Come to think of it, I like your
option (b) too!  Intriguing stuff.

Peter wrote:
> Paul will have to work out the current/voltage profiles over the
> radial dimension of the flat coil.
Yup, for both primary and secondary, rather than just the secondary
as we usually settle for - this if we want to take account of 
mutual C, not just mutual L.

Terry wrote:
> If inductive is 99.9% and capacitive is 0.1%, then maybe it is
> simply not a concern in any case.  But if it is 90% 10% or
> something like that, it may be a big deal. 

I tried a few flat spiral high-K transformer designs for a matching
transformer, but the high pri-sec C was a major headache. I only
modeled the bulk C but that was enough to put me off.

Someone needs to have a play with acmi to see what sort of
separations are needed to achieve a suitable TC k.  A parallel
plate estimate would then give you the mutual DC capacitance, say
halve it to get a ballpark estimate of the effective C coupling the
hot ends of the two windings.  Then turn to your circuit sim...
that should be enough to tell whether mutual C is worth worrying
about.  If it isn't, it would save me doing a whole mess of code. 

--
Paul Nicholson
--