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Re: Optimal Topload?
Subject: Re: Optimal Topload?
Date: Sun, 11 May 1997 12:19:35 -0500
From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
> Date: Sun, 11 May 1997 00:37:12 -0500
> To: tesla-at-poodle.pupman-dot-com
> Subject: Optimal Topload?
> From: Tesla List <tesla-at-pupman-dot-com>
> 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
>
>
Fr. Tom,
What kind of cigars do you smoke? : )
Your idea of the optimum topload employing an inverted cone starting
with a rolled edge (bottom toroid) near the top of the secondary and
only slightly larger than the secondary diameter, and then becoming a
large overall diameter terminating in a large R.O.C. toroid (rolled
edge) on the top is indeed the idea I have successfully employed.
You mention that the top could possibly become a hemispherical dome
and I agree that this justifies experimental trial but fabrication is
more difficult. I haven't tried the hemi version myself yet.
I think that the larger the secondary the more effective this type
topload may be from a practical standpoint.
In my own experience, the electroststic field control of this shape
does a great job preventing breakout near the coil. Streamers will
tend to walk only around the top toroid.
I first tried such a shape over two years ago on my first coil which
employed a 30 inch diameter secondary about 60 inches long wound with
#8 AWG PVC stranded wire (when I get really interested in something I
always tend to get carried away). Interestingly enough I first employed
it
upside down like a mushroom cap. It did a fantastic job throwing the
streamers down around the secondary coil and none up and away! I
simply turned it 180 degrees and voila! The toploads I usually
employ consist of two toroids without the interconnecting conical
sheet metalwork. By virtue of their differing sizes and spacing the
field control which would be provided by the missing sheet metal is
almost as
good.
I should point out for the record that R. Hull and his associates at the
TCBOR
have been using these filled conical toploads very successfully to
control the
intense fields around their highly stressed minature resonators in
their magnifier work. It is in great part the tremendously superior
field control provided by this shape which makes 10 foot long
streamers from a 1 foot long resonator possible. For the extra coil
I believe they use such a shape on both ends of the coil.
I think that such a technique, to use a conical field control shield
at the bottom of a classical two coil design may be the answer to
exceeding 3-4 times the secondary length in streamer activity, but
this bottom shape will be hard to implement without A). being a shorted
turn, and B). still permitting optimum coupling of the primary, since
ideally the cone should launch off the bottom end of the coil. I've
actually prototyped a very small tabletop unit employing such an
idea, but it does not outperform a regular coil, and that could
easily be because tiny tesla coils are just not that successful
anyhow. I need to make a normal, (as in large) test model to really
see if there are advantages to be found in this direction. This is
experiment number 2,027 to be tried next.
I cannot advise what the best angle would be for the cone shape , but
I've generally employed either a cone or progressively larger O.D.
toroids such that they are seen expanding along a straight line at
about a 30 degree upwards angle from the plane of the topmost
secondary turn. For me this has worked very well.
On my MTC unit for example the control donut is 3 inch cross section
by 18 inches O.D. spaced about 5 inches above the 15.5 inch diameter
secondary. About 8 inches above the control donut is the discharge
donut measuring 12 inches by 48 inches. This arrangement throws the
streamers either horizontally or upwards. Primary rail strikes are
rare and when this happens they come only from horizontally launched
streamers off the top toroid that have done an after launch downwards
direction change. Clearly there is excellent field control. In much
reviewed videotape of MTC runs there have been ZERO streamers or
corona issue from the top of the secondary winding, or its
field/corona control donut.
What I'm trying to figure out is how to build one of these shapes
that are maybe 24-30 feet in diameter, 15 feet or so tall, and be able
to transport
one in an 8 foot wide trailer.
Maybe I shud check the ACDCX list for a surplus space distortion
field generator with portable power supply. " Oh, oh, honey, I shrunk
my bank account".
rwstephens