Pseudo Toroid Design
From: Thomas McGahee[SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent: Sunday, November 09, 1997 2:16 PM
To: Tesla List
Subject: Pseudo Toroid Design
> From: Chuck Curran[SMTP:ccurran-at-execpc-dot-com]
> Sent: Saturday, November 08, 1997 12:09 PM
> To: tesla-at-pupman-dot-com
> Subject: Toroid Design Features
> Hello All:
> I'm in the process of deciding on how to prioritize coil improvements for
> the next few winter months. Near the top of the list is the toroid. I am
> going to get pricing for a spun aluminum toroid and that is where a question
> pop's up right away.
> Many of us have made a toroid using a similar set of design features.
> Specifically, a flat center disk surrounded by the "Donut". The large
> radius Donut clearly prevents the premature spark breakout, but results in a
> shape that may increase the cost of a spun aluminum item. Here's the real
> question. When I draw up a design to take to a local spinning supplier, I
> would like to have as much flexibility as possible to control the cost. I
> see a toroid that would be, let's say 10" thick with a 5" edge radius as
> being just as effective as one with the 10" diameter outer donut coupled to
> a thin center disk. I hope the cost would also be lower. The capacitance
> should be almost identical too. Have I missed something here, or would the
> thick top hat be just as effective? We have many local metal spinning job
> shops and any flexibility in the design would sure be a benefit. Thanks in
> advance for any comments.
> Chuck Curran
What makes a toroid so good for TC use is its ability to shape the e-fields
so that breakout is supressed at the top and bottom, and instead tends to
occur at the outer rim of the toroid.
The inside of the toroid actually contributes next to nothing to the toroid's
characteristics. In fact, if you look at Tesla's patent drawings you will find
that he leaves the inner section out completely. He also shows the toroid's
surface as being composed of many small half-spheres. The interesting thing is
that the mutual action of the surface e-field shapes of a toroid-like structure
is such that it will tolerate a fair amount of surface irregularity and still
act as if it were perfectly smooth.
Simplification: Concentrate on making the outer rim and enough of the top and
bottom of the toroid shape smooth enough to be useful. Do not worry about the
inner part of the topload, as it adds nothing to the toroid's usefulness in
Imagine that you had two 31.4 foot lengths of thin-wall aluminum pipe with a 2
diameter. If you could "roll" these somehow into two big 10 foot diameter
you would have the beginnings of a huge toroid. I say the beginnings, because
you could use these two large circles of pipe as a sort of glorified corona
guard for a sheet of aluminum 31.4 feet long and say two feet high.
Roll the sheet of aluminum into a circle about ten feet in diameter. use pop
rivets or whatever to join the ends. A short strip of metal on the inside can
be used to join the ends so there is no bulging overlap of the actual sheet.
Now mount the two large metal tube rings, one along the top, and the other
along the bottom. The idea is to let the metal tube rings shield the sharp
upper and lower edges of the sheet metal cylinder. The rings can be attached
quite readily by using sheet metal screws and affixing the sheet metal to the
INSIDE of the tube rings. Don't worry about corona. The inside of the ring is
When finished you will have a pseudo-toroid that has a tremendous outside
surface area and fairly reasonable corona protection at the edges. You can
create a suspension mechanism by having an inner metal plate (reasonably thick)
with holes punched around its rim connected via guy wires to the aforementioned
sheet metal screws that hold the outer sheet and tubular rims together. The guy
wires would then connect up like bicycle spokes to the inner metal hub.
If the guy wires are attached to the lower rim and made to be a bit longer
than required, then the hub will be connect to these guy wires at an angle such
that the hub allows the lower rim to hang significantly below the hub. That
allow greater shielding of the top of the secondary coil.
Properly connected such a suspension mechanism would make a simple central
support structure. The total weight of the pseudo toroid would be small
compared to its effective capacitance size. The neat thing is that such a
design can be effectively carried out without recourse to expensive and
hard to get parts.
Bending the corona guard rings is the hardest part. If the diameter of the
ring is large, then the bending is easier, at least as far as applied force
Of course, there is nothing to stop you from using dryer duct as the
corona guard, but then you may need to strengthen the assembly with
some form of internal framing. Because the inside is effectively shielded,
you could easily get away with using almost anything for the internal framing.
If you do go with aluminum tubing, you can make a simple tubing bender out of
sturdy wood, such as two by fours. What you do is build a wooden section of
an arc covering several degrees. The tubing is then bent around this arc
piece by piece, just like with an electrician's tubing bender. Note that such
tubing benders have one side designed so that it grasps the pipe during
bending, but then allows it to slip forward a few inches for the next bend
sequence. You are all smart people. Figure out your own modifications.
Modify the basic idea as needed. It can be scaled up as well as down. Use your
own ingenuity and exploit the materials that YOU have readily available.
Hope this helps.
Fr. Tom McGahee