Flat Primary Winding - next question

From:  Malcolm Watts [SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent:  Wednesday, June 17, 1998 6:58 PM
To:  Tesla List
Subject:  Re: Flat Primary Winding - next question

Hi Larry,

> From:  Larry Bud Melman [SMTP:gasman-at-althea.a-line-dot-net]
> Sent:  Monday, June 15, 1998 10:35 PM
> To:  Tesla List
> Subject:  Re: Flat Primary Winding - next question
> > This leads to another thought.  If the primary effectively couples mainly
> > to the lower part of a 1000 turn secondary (e.g. the first 100 or so
> > turns), then do we in effect have a 100 turn secondary feeding a 900 turn
> > third coil?  In other words, does a conventional TC function as a merged
> > combination of pulse transformer and magnifier extra coil?

Experiment suggests this is true. Overall Ksys for a magnifier depends
on Kdriver and the proportion of total secondary in the driver i.e.
Ksys might follow a law something like:

    Ksys = Kdriver x Lsec/(Lsec + Lextra)

Plugging the figures in from my own little magnifier setup shows this 
isn't the correct law but you get the idea. Taking the square root of
Lsec/(Lsec + Lextra) seems to get close.  Must check sometime.

>  I envision the
> > transition zone from conventional two-coil TC to magnifier extra coil would
> > be a gradual effect, depending on how the primary magnetic flux was shaped
> > and intercepted the secondary.  I suppose the answer to this probably
> > doesn't affect how to build decent coils, but perhaps it could lead to
> > better understanding of how our beloved TCs actually do their thing. 
> > Comments?
> > Lastly, wouldn't it be interesting to actually map the magnetic flux
> > between primary and secondary (and floor and whatever else) to better
> > visualize how concentrated or distributed the magnetic coupling actually
> > is?  I have seen posts which suggest the visual purple air ionization
> > visible between primary and secondary has something to do with magnetic
> > coupling.  I believe the effect is purely high voltage ionization of air
> > and is not an indicator of anything going on magnetically.  Comments?


>     Wow.  I'm a relative newcomer here, and the amount I learn from reading
> these posts is amazing.  Two weeks ago, I didn't even know what a magnifier 
> *was* (not that I can exactly explain it now, except that it has a third
> coil which is not magnetically coupled to either of the first two <g>), but
> anyway...
>     As I read this post, a potential qualitative way of getting an idea
> of just how big the field from the primary is at different heights came to mind.
> I wonder if it would be useful:
>     Remove the secondary (as I'm sure one might not wish to get zapped with
> the output from some TC's - or, at least for sure, the dreaded warthog <g>).
> Then, just fire up the primary circuit and let it go.  Get a piece of paper 
> covered with ferric dust, start at a height corresponding to the height of the
> sec'y, and see if the dust is perturbed.  Move down slowly.....

Not a good idea unless you want to wreck your primary capacitor. 


>     Of course, this might not do anything, as most coils, from what I've
> read, seem to operate at frequencies in the ~50-60 to 300 kHz range, and such
> high frequency oscillations may have no effect, even on ferrite *dust*, at 
> least until you get into relatively higher field values.
>     I guess a wire with a milliammeter on it would accomplish the same thing
> more reliably...
>     Cheers to all.
>                         Clay Wilson