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multi-layer secondaries: problems




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From:  Thomas McGahee [SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent:  Sunday, February 22, 1998 10:50 AM
To:  Tesla List
Subject:  multi-layer secondaries: problems


> ----------
> From:  Mike Harrison [SMTP:wwl-at-netcomuk.co.uk]
> Sent:  Saturday, February 21, 1998 5:02 PM
> To:  tesla-at-pupman-dot-com
> Subject:  Re. multi-layer secondaries
> 
Snippity-doo-dah

> >>"Another thought - it is possible to imagine a multi-layer coil layered
> >>the 'other way', effectively a stack of concentric spirals going
> >>alternately in and out, e.g. for 3 layers,the turn numbers being
> >>something like :
> >>
> >>   | |
> >>987| |789
> >>456| |654
> >>321|_|123
> >>

Mike,
Actually you would not gain much of anything with this method.
Let me illustrate this by showing you that the maximum voltage
between adjacent windings (such as 1 to 6  and 4 to 9) is a
difference of 5.

Now if you wind the coil segments as conventional 'pies', then
you get something like this:

   | |
987| |789
654| |456
321|_|123

Now the greatest 'difference' is 3. In fact, the 'difference'
between ALL adjacent turns is 3.

In the winding plan you envisioned, the 'difference' between
adjacent sections varies between 1 and 5. The average is still
3, but with peaks of 5. Not good. 

Note, by the way, that 'pies' achieve their constant 'difference'
voltage by having the wire from the outer section of one 'pie'
connect to the inner section of the next 'pie'.

Pies do have their negatives. You have to route the outside
of one to the inside of the next. That does require some room
to do that, with adequate insulation on the connecting wire.

'Pies' are very easy to build, and you can make each one
separately and then wire them together. That makes the task of
winding the HV coil a lot simpler in practice.

For *HV* applications, you really cannot beat the 'pie' method.
Wave winding and the like were designed to reduce the self-
capacitance of the coil. From a voltage difference standpoint, 
wave winding is horrendous. 

*****
BTW, if I really wanted to wind the kind of coil you envisioned, here
is how I would do it:

Imagine an inside core 1" in diameter and an outside cylinder 2" in
diameter. Start by placing an end circle at the bottom of the coil. 
This end circle would have a diameter of 2". Begin by winding the first
section from the inside to the outside. Slip the outside cylinder up
beyond the first section. Now, pushing the wire around the inside of 
the outer cylinder, work the next spiral section INWARD. When you 
reach the core, spiral up the core a bit and then continue winding the
coil outward until you get to the 2" diameter point. Then carefully
slide the outer cylinder upward, and pushing the wire around the inside of 
the outer cylinder, work the next spiral section INWARD. Continue
these steps until all sections have been completed.

I would imagine that after a few sections have been done that it would be
hard to slide the outer cylinder up, due to friction. One way you
could get around that problem would be to have the outer cylinder
composed of rings of insulating material that would interlock and
allow the cylinder to 'grow' a few sections at a time. Of course, you
would still have to deal with the problem of getting the sections 
over the wire. All of this is do-able, but what a mess of complications
to do something that ultimately will give you almost no real gain.

My desire in sharing these thoughts with you is not to shoot the idea
down, but rather to point out some areas that I think you would want
to know about that directly relate to your idea. Your idea is *not*
that unwieldy if applied to building a multi-level *primary* out of
copper tubing. I have built such things in the past, and if I am 
not mistaken, I think that Malcolm Watts has done the same. You have
to heavily insulate the two sections of such a primary, and I would
not use less than 1/4" plexiglass. You also have to be careful about
the upper layers, as they just LOVE to arc to the secondary!!!

Hope this helps.
Fr. Tom McGahee