Stefan's Tesla-Pages

The toroidal discharge terminal

In the first 3 sections, I'll post some text from other coilers like Richard Quick, Ed Sonderman and Bill Beatty. I found them somewhere in the web (collected mails etc.). They describe the construction of the most common type of discharge terminal, the toroid. I only converted the ASCII-text in a HTML-version. Below, I placed some information on all my homemade toroids.

• Richard Quick
• Ed Sonderman
• Bill Beaty
• Greg Hunter
• list of my homemade toroids and how I use them
• how I made my T10 out of corrugated plastic drain pipe
• how I made my T11 and T14 out of flexible round aluminum ducting

Richard Quick:

Clearly the toriod is the ultimate in high Q discharge terminals for Tesla systems. Now go out and buy one. I can hear my friend Dave Halliday now..... "You paid _HOW MUCH?_"!!!

Yup, spun aluminum toroids are available commercially, and they run hundreds, even thousands of dollars each. My 20" wide by 5" high commercial toriod ran me over 350 clams. My ten inch secondary needs a toroid at least twice that big to achieve optimum performance, and as commercial toroids get larger, the price increases exponentially. I priced a 40" toroid for my coil at $2000.00 not including shipping, and they gave me a six month delivery time...

Considering the time, money, and performance; by far the best way to obtain toriods is to build them from scratch. Basically we are looking for a fairly smooth ring or donut shape that has a flat plate mounted in the center. The entire surface needs to be conductive. As long as these simple guidelines are met, any way you can build one will work fine; but generally there are several approaches.

1) The first method, and my personal favorite, uses a ridged or "corrugated" black (or yellow or...) flexible polypropylene drain piping that is commonly found in hardware, plumbing, and construction supply dealers here in the states. It is found in a variety of sizes, four inch and six inch dia. being common. This flexible piping can be cut into suitable lengths and easily bent into a ring of the desired size (a heating gun may help). I match the ends up, and use 3 inch wide plastic adhesive tape to hold the two ends together.

Once the ring is made, I use strips of 3 inch wide plastic adhesive tape to smooth out the ridges (or corrugations) in the surface. These strips of plastic tape also provide a surface on which the conductive layer is applied. Next I obtain a roll, or two, of specialty "plumbers tape". This tape is found at the same dealers that handle the flexible plastic drain piping mentioned above, and is commonly available in two widths, 1-1/2 inches wide, and three inches wide. This tape is really just a roll of heavy aluminum foil that has a thin adhesive backing.

Strips of the aluminum foil "plumbers" tape are cut and applied in overlapping sections on the plastic ring until the entire surface of the ring is covered and has a conductive surface. Next a disk or circle of thin plastic, masonite, wood paneling, etc. is cut so that it friction fits inside of the conductive ring. Lay the toriod on the floor and center the disk in the middle of the ring. Set some wood blocks, books, or other spacer beneath the center disk to hold it in place in the middle of the conductive ring. Glue, plumbers tape and/or strips of glue covered metal foil are placed around the edges where the flat center contacts the outside conductive ring; this holds the center plate in place. Next I use a high quality spray adhesive to coat the center plate, and cover both sides of the plate with heavy duty aluminum foil.

This basically completes the construction of this type of homemade toriod. Strips of aluminum foil coated with a high quality spray adhesive may be substituted for the commercially made aluminum plumbers tape.

2) A second type of homemade toriod uses a commercially manufactured flexible round aluminum ducting to form the donut or ring. This ducting is available from commercial building suppliers, heating and air-conditioning companies, and occasionally a hardware store. The material is rather fragile, and will dent easily. (Therefore you should not stretch it out but leave it in its compressed shape as it is when you buy it. This measns the maximum toroid diameter is determined by the compressed length of the ducting which then will equal the inner diameter of the toroid) A ring is fashioned and the ends are glued or taped. The conductive center plate is constructed and mounted exactly the same as in the instructions above.

3) Another material available in the states is a round flexible stainless steel piping sold as a replacement chimney liner. This material is tough, flexible, and corrosion proof. It is sold for relining chimneys in older houses where the original liner has decayed. It is more expensive than the aluminum air ducting, but you would need a hammer to dent this material. The ring could be riveted or even welded together, although tape or glue would probably work. The conductive center plate would be constructed as outlined in the instructions above.

4) Another homemade toriod design uses sections of rounded stove pipe elbows fitted together to make a conductive ring. Again the center plate is constructed as outlined above.

Do not worry about a perfect and solid connection between all sections of a homemade toroid. Overlapping foil with an adhesive layer between may show a poor or non-existent connection when measured with the VOM, but in practice the skin effect makes this a moot point. The toriod will be function perfectly even if all sections are not perfectly electrically bonded.

In practice a homemade toriod can be put together from scratch in a few hours with almost no tools and very little money. The performance is nearly identical to a commercially made toriod costing hundreds of dollars, though typically homemade toriods do not have the "polish" that commercial toriods have. Trust me though, then the lights are down, and the sparks are flying, nobody notices glue splotches or other imperfections on the surface.

Richard Quick
...

...

From Ed Sonderman, RE: Toroid Mounting

I use the following method to mount my toroid. On top of the secondary plastic end plate, I glued a pvc end cap for 1.0" dia pvc pipe with the open end up. It helps to sand or turn it on a lathe to get it nice and flat. Now I insert a short piece of 1.0" dia pvc pipe of the height desired (I am using about 6.0" now). Do not glue it. Then I take another end cap and flatten the end off again and drill a 1/4" hole in it. Then I insert a 1.0" long 1/4 x 20 nylon screw through the hole from the inside. Place a piece of tape over the head to hold it in place. Now place this cap on the stand off pipe. My torroids all have a 1/4" dia hole drilled through the center. I set the torroid down over the screw, using a large nylon washer and tighten it down with a nylon wing nut. I have the top 2.0" of the tail of the secondary wire stripped bare and wound into a loop. I place this over the screw before sitting the torroid in place. So it gets clamped into place when the wing nut is tightened. This achieves a mechanical and electrical connection at the same time. The end caps make it easy to change pipe lengths and the attachment method allows easy changing of torroids. Which I never thought would be a problem but now I have three.

I now wish I would have gone with 2.0" dia pvc caps and pipe since my dischargers have grown so large - for more stability.

(Editors Note (RQ): Ed went to mounting an end cap for three inch diameter PVC plastic pipe to obtain the stability he was looking for)

I am just completing my newest torroid and should get it fired up tonight. It is again made of 5.0" dia corrugated black plastic drain pipe. I used about 9.5 feet of drain pipe and a 30" acrylic disc for the center. Finished, it is about 40.0" in diameter.

Ed Sonderman
...

...

Bill Beatty:

Making an upper Toroid terminal

I've made a couple of small (1ft x 5in) toroids from florist's foam, that crunchy green stuff, bought from a foam supply co. in Seattle. I "cheated" by forcing a big block of foam down onto a 5" PVC pipe and sculpted it on a lathe using an old file as a scraper. I then painted it with resin and coated it with that adhesive foil tape sold in hardware stores (downspout repair tape? Metal duct tape?) I burnished the tape down with a spoon. Works great! I bet you could make a very large terminal this way by building a hot-wire bandsaw and using blocks of styrofoam. The surface needs to be painted with polyester coating or something similar, to give the foil tape something smooth and solid to stick to.

Another possible technique is to cover a large balloon with several layers of Elmer's-glue-wetted newspaper strips, then while it is still wet, carefully crush the balloon into a torus shape with some sort of wooden bracket (like a big, crude C-clamp) When dry, this papier-mache form can be coated with the same adhesive foil as above. This technique was used by a hobbyist in Wisconsin to create 4ft diameter VandeGraff terminals of various shapes.

- Bill Beaty

...

posting from http://www.pupman.com/listarchives/2001/June/msg00309.html

Paper Mache' Toriod Rules!

To: tesla@pupman.com
Subject: Paper Mache' Toriod Rules!
From: "Tesla list" <tesla@pupman.com>
Date: Thu, 07 Jun 2001 21:01:25 -0600
Original poster: "Gregory Hunter by way of Terry Fritz <twftesla@qwest.net>" <ghunter31014@yahoo.com>

Dear List,

I just made a new toroid for my 6" x 30" pole xfmr Tesla coil system. It is based on a vinyl swimming pool toy I bought at Wal Mart for $1.44. Inflated as hard as I could do it with lung power, the thing appeared to be absolutely round, concentric, and perfect. I covered it with several layers of paper mache' using 50:50 Elmer's white glue & water and newsprint. It looked wrinkly at first and I wasn't happy with it. However, as the glue/water dried, the newsprint strips shrunk and pulled all the wrinkles out, leaving a smooth, drum-tight surface. Cool!

Application of the paper mache' proved to be a tedious, time-consuming business. The project stretched into days, I got sick of doing it, and the paper skin was still too thin. Finally, I got a brainstorm and wrapped the thing with bands of plain white cotton bedsheet material that happened to be in my wife's sewing scrap collection. The cloth covering was very absorbent, and it soaked up plenty of glue/water, followed by several sloppy coatings of clear gloss urethane varnish. The varnish & glue-soaked cloth hardened into a stiff shell--just what I wanted.

Once the thing dried, I used four, 30-foot rolls of Aluminum HVAC tape to cover it. The center got a 1/2" x 10" plywood disk covered with foil and cemented in place with silicone glue. Finished dimensions are 8 inch chord and 26 inch diameter. It's very nice looking--glossy smooth. Sorry, no pictures yet.

Before, I was using a car tire inner tube covered with foil. The inner tube toroid was lopsided, wrinkly, and just unbearably ugly. I only tolerated it because it worked so well and boosted my spark length. The new, bigger, slicker, prettier 8" x 26" toriod works even better. The sparks have outgrown my garage with its 8-foot ceiling. Streamer hits to the walls & ceiling are thick and Xenon lamp blue.

The finished product is satisfying in every way. However, if I had it to do over again, I wouldn't. I'd get me some 8" Aluminum flex-duct and form that around a couple of Aluminum pie pans. The pool toy toriod took many days and uncountable hours. A flex-duct toriod could've been knocked together in an evening.

Actually, I've gotten little benefit from the better performance because the garage is just too small for the setup to really show it's stuff. For that, I'm going to have to move outdoors. I don't know if that's a real good idea though. My country neighbors are the best folks in the world, the salt of the Earth, and I love them, but I just don't think they'd understand or appreciate the lightning machine spouting sparks in my driveway. I'm already somewhat of a foreigner in this little rural town. After all, I'm...you know, Methodist!

Regards, Greg

This is a list of all my homemade toroids:
(standard configuration for my coils in bold)

Capacitance values calculated with the formula given below the tables.

TTTC1 (2"-coil):
#	D [cm]	d [cm]	Ct	material	mainly used as
T9	22.5 (8.9")	3.1 (1.2")	8.74pF	.	.

Vitamini (1"-twin-coil):
#	D [cm]	d [cm]	Ct	material	mainly used as
-	?	?	(?)	.	anti-corona-ring for twin_1 (the inductively driven one)
T2 (?)	10 (4")	2.4 (")	4.38pF	.	.
T4	17.2 (6.8")	6.2 (2.4")	7.49pF	.	main discharge toroid for twin_1 (the inductively driven one)
(?)	(?)	(?)	(?)	.	(kleines mit Loch)
T5	19.4 (7.6")	4.6 (1.8")	8.49pF	.	main discharge toroid for twin_2

2"-coil:
#	D [cm]	d [cm]	Ct	material	mainly used for
T12	35.5	10.8 (4")	15.73pF	4" alu vent tubing (not stretched => robust)	main discharge toroid for 2"-coil
T9	22.5 (8.9")	3.1 (1.2")	8.74pF	.	below the big cone
big cone	.	.	.	.	(high capacitance with a small diameter => great for small basements :-)
T3	13.5 (5.3")	3.6 (1.4")	5.97pF	.	on top of the big cone

4"-coil:
#	D [cm]	d [cm]	Ct	material	mainly used for
T6	22.7 (8.9")	5.7 (2.2")	9.99pF	2" alu vent tubing	anti-corona-ring for the 4"-coil
T11	59 (23.2")	10.8 (4.3")	24.7pF	4" alu vent tubing (not stretched => robust)	new main discharge toroid for 4"-coil, perhaps it will be replaced by T14, my planned 6"-toroid, in the near future
T14	70 (27.6")	17 (6.7")	30.7pF	centerplate diameter 40cm (thickness 15cm), grooved	brandnew main discharge toroid for 4"-coil
T8	64 (25.2")	11 (4.3")	26.40pF	4" alu vent tubing (stretched => very fragile, dented!)	old main discharge toroid of the 4"-coil in Aug.'97
T10	45 (17.7")	17.5 (6.9")	19.29pF	6" drain pipe (extremely robust)	new for 4"-coil

8"-coil:
#	D [cm]	d [cm]	Ct	material	mainly used for
T7	36.5 (14.4")	5.6 (2.2")	14.62pF	.	anti-corona-ring for the 8"-coil, perhaps I'll use T12 instead, because it has a higher radius of curvature
T13	approx. 125 (50")	17 (6.7")	48.37pF	planned (6" drain pipe or up to 12"alu vent duct), 95cm diameter center plate (green styrofoam stuff)	main discharge toroid for 10"-coil, it will sit on a big speaker basket (D=45.5cm/d=18.5cm/h=14cm, thank you again, Finn!)
T12	35.5	10.8 (4")	15.73pF	4" alu vent tubing (not stretched => robust)	main discharge toroid for 2"-coil
T8	64 (25.2")	11 (4.3")	26.40pF	4" alu vent tubing (stretched => very fragile!)	old main discharge toroid of the 4"-coil in Aug.'97
T10	45 (17.7")	17.5 (6.9")	19.29pF	6" drain pipe (extremely robust)	new for 4"-coil

Others (the ones not used in standard configurations and some additional spare parts):
#	D [cm]	d [cm]	Ct	material	.
small sphere	.	approx. 2"	.	.	.
medium sphere	.	approx. 4"	.	.	.
small cone	.	.	.	.	(high capacitance with a small diameter => great for small basements :-)
T1	8 (3.2")	2.4 (0.9")	3.55pF	.	.
-	8.3	3 + 5.6 half sphere on top	.	.	.
T3	13.5 (5.3")	3.6 (1.4")	5.97pF	.	.
T4	17.2 (6.8")	6.2 (2.4")	7.49pF	.	.
T5	19.4 (7.6")	4.6 (1.8")	8.49pF	.	.
T8	64 (25.2")	11 (4.3")	26.40pF	4" alu vent tubing (stretched => very fragile!)	old main discharge toroid of the 4"-coil in Aug.'97
T10	45 (17.7")	17.5 (6.9")	19.29pF	6" drain pipe (extremely robust)	new for 4"-coil

Ct=(1.28-d/D).sqr(2.pi.d.(D-d)) with D,d in inches

Go to the 'How to build the perfect secondary'-page for some hints on how to find the right toroid diameter and a schematic how to place the toroids onto the coil.

Some words about how I made T10:
I found a length of 5.5m plastic drain pipe (the yellow corrugated stuff with 6" diameter) and cut it to the required lenght. With a pair of pliers I flattened the corrugations on the inside of the planned toroid to make bending easier (it is a VERY stiff material!). With a heavy wire inside the pipe I bend it into a big half circle. By shortening the wire step by step and heating the whole thing with a heat gun, I bend the halfcircle narrower until I had a circle of the planned inside diameter of 5". I flatted the ends of the pipe (the 'meeting point') with a knife and the heat gun. Then I wrapped a heavy tape around the outside perimeter of the toroid. After that step I upholstered the area around the 'meeting point' for an more even radius of curvature. Then I wrapped the outside of the toroid again with the heavy tape, but this time in a 'wiggled' way to cover the outside half of the toroid with the tape and make it smooth. Next I covered the whole thing with self adhesive aluminium 'plumbers tape'. Then I placed a wooden disk (5" dia) in the middle of the toroid (pressed fitting). I fixed it with hot glue. As a last step, this middle plate was also covered with plumbers tape. To make a perfect smooth suface, I used a spoon to smooth all surface imperfections out.

Some words about how I made T11 and T14:
T11 is made out of 4", T14 out of 6" alu vent duct. I left it in its compressed state, so it remains very robust. As a centerplate, I used a plate of the green styro stuff, 4" thick for T11, resp. three white styro plates each 2" thick (stacked to give me a 6" one) for T14. I cut it in a circle of 40cm diameter and sawed a groove around its perimeter, looking like this in cross section:

   ____
  >____< 

T11: I bent the duct into a circle and wrapped a heavy tape around the outside perimeter of the ring.
T14: I bent the duct into a circle and pressfitted a 4" long piece of 6" PVC tube into the ends to join them (works VERY well !!!).

After that step I placed some strips of self adhesive aluminium 'plumbers tape' over the area around the 'meeting point' for an more even radius of curvature. Then I slipped this ring over the centerplate (pressed fitting) and fixed it with hot glue. It now looked like this:

 _ ____ _
(_)____(_)

Next I covered the top and bottom side with some more self adhesive aluminium 'plumbers tape'. To make a perfect smooth suface, I used a spoon and then a piece of cloth to smooth all surface imperfections out.

The last step is very important: the side of the toroid where the ends of the alu vent duct are joined has more weight than the opposite side. Therefore we have to balance it to prevent it from fallling down from the coil accidently (been there, done that...). It's easy to do by screwing some old screws (form the junk box with the unsorted stuff) into the styro until it is balcanced out. Cover the area with the screws with one more strip of plumbers tape.

Therefore I will make an insulating slit into my toroids soon.