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Optimal Topload?
Subject: Optimal Topload?
Date: Sat, 10 May 1997 22:34:10 -0400
From: "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
To: "Tesla List" <tesla-at-pupman-dot-com>
This post seeks to answer two separate posts,
one by Doug, and one by rwstephens
>Subject: spheres vs. toroids, or both?
> Date: Sat, 10 May 1997 02:41:49 -0400
> From: des <des-at-ellijay-dot-com>
>Organization: dcs
> To: Tesla List <tesla-at-pupman-dot-com>
>
>After reading Fr. McGahee's post regarding spark length vs. toroids,
>recognizing the advantages of both the toroidal and spherical
>toploads,
>I wondered if anyone has tried using a toroid on top of the
secondary
>for shielding, then placed a sphere into the top of the toroid to
add
>capacitance? Any ideas of whether this would be worth trying? I
have >a
>toroid, and would consider making a large sphere to set into it, if
it
>seems like it would be of any advantage.
>
>doug
----------
>
BIG SNIP
>
> Fr.Tom,
>
> What about employing a rather small radius of curvature toroid just
> above the top secondary winding for electrostatic field control (I
do
> this on all my larger coil systems successfully) and then having
> taken care of corona breakout from the topmost windings of the
coil,
> let's get down to business up here making a top terminal that
cooks!
>
Precisely! It is often best to break a problem up into its component
parts and then apply specific solutions to each component part,
rather than trying to find a "one size fits all" solution.
Corona guards are often small toroids mounted at the top of a coil
whose specific task is NOT large spark production, but simply corona
reduction. In the same way a relatively small size toroid can be
given the job of shielding the top of the coil, and leave the BIG
capacitance job to a sphere.
It would seem to me that you would not want the sphere too close to
the toroid, however, or the full capacitance of the sphere might not
be realized as fully as it should. Keep in mind that anything that
appears to be on the INSIDE of a toroid will ALSO be shielded, and
that includes a sphere sitting too close to the toroid.
> As I see it, once you have taken care of shielding of the top of
the
> coil, above that you should be able to employ a sphere, so long as
> the diameter/spacing of the topload protection toroid is adequate.
>
> Although what I am postulating here is probably a good idea, I will
> not use this as I have come up with a better shape to throw
streamers
> up and away, and miraculously, I came up with it by experiment
using
> REAL HARDWARE.
>
> Please pitty me and understand that I am handycapped. Unlike many
> others, I have no spreadsheets, no Teslac or similar programs,
> absolutely no CAD programs, etc. I have to simulate everything I
do
> in reality. I admit, this costs real money as opposed to simulated
> money (wrong forum to discuss the fact that these are now the
same), and
> real
> time as opposed to time compaction simulation, but
> somehow I manage........and oh yeah, somehow I also get REAL
results.
> MMMMMMMMM smell that ozone! : )
>
> rwstephens
rwstephens,
You have thrown us a tantalizing tidbit in the above post, mentioning
that you have a better shape. Now that you have our attention, how
about sharing your concept with us? I couldn't care less if you are
"handicapped" as you put it. There is NO substitute for reality!!
While we await your post concerning the shape you have devised, let
me share some of my own thoughts on the "perfect" shape. Not perfect
in all regards, but perfect for most coilers in actual practice. My
own SUPER-SHAPE would take the following form: Imagine a toroid near
the top of a secondary, somewhat smallish in size, but adequate to
shield the top of the secondary. Imagine a much larger toroid a foot
or more ABOVE the smaller toroid. Now imagine that the two toroids
are connected together by a piece of sheet metal formed into a
section of an inverted cone. The section of the cone would touch each
of the toroids at or near their widest points. The sheet metal would
GREATLY increase the topload capacitance, and because if its large
radius of curvature would NOT promote discharge breakout. That would
occur at the top toroid in the usual fashion.
A POOR MAN'S VERSION of this can be whipped up quite easily by any
coiler that owns two toroids and some sheet metal. Let's assume that
you have two identical toroids. Attach the first to the secondary AS
USUAL. Using the same flashing that we use to make capacitor plates,
simply make a large metal tube and sit it on the first toroid. You
could handle the seam problem by hot gluing the sheet metal to a
strip of wood placed INSIDE the tube along the seam, or you could
wind several turns of the flashing around to form a tube with
increased strength if needed. In this case you might have to use
something ugly like duct tape to hold the outer turn down. Now place
the second toroid on top of the tube you have formed. TA DAAAA! You
now have something that is equivalent to SEVERAL toroids as a
topload, but MUCH easier to build!!! If you don't use a second toroid
then you will get really excessive corona loss and reduced spark
length.
The advantage of the inverted conical section versus the tubular
shape is that you definitely move the area that wants to break out
UPWARD and AWAY from the top of the coil. The tubular method would
only work well with larger toroids, and though it would definitely
increase the topload capacitance, you would find that the bottom
toroid might well be where breakout occurs, rather than the top
toroid. Of course, you can always use a bump on the upper toroid to
focus breakout, but this might not be optimal.
I am aware that you could get even MORE capacitance if the TOP toroid
was replaced by a sphere sitting on the metal tube, but it is also a
LOT harder to implement, and all of the sphere that lay within the
tube would be wasted as far as capacitance is concerned.
I would be *amazed* if no one else has actually done what I have
outlined above. But, I have not run across any mention of such an
arrangement in my readings of this list's archives, and so I put it
forward here in the hopes that if it HASN'T been tried, that now it
WILL be tried. And if it IS something that has been tried, well,
then, it is always GOOD to bring forward such things if it so happens
that they are not widely known.
In the hopes that shared ideas will help us all in our quest for ever
bigger and better sparks!
Fr. Tom McGahee