From richard.quick@slug.orgWed Aug 23 21:32:56 1995 Date: Wed, 23 Aug 1995 22:16:41 -0600 From: Richard Quick Reply to: usa-tesla@usa.net To: billbeskimo.com Subject: TOROIDS Quoting Henry.Gessau@abc.se (Henry Gessau): > Could you share a bit your knowledge of toroids for T.C.s? > E.g: > - Advantages/disadvantages of toroids vs. spheres > - Size of toroid/sphere required > - Obtaining/constructing toroids/spheres Toroid Discharge Terminals Another feature of the "classic" Tesla coil design is the sphere or ball discharge terminal. Tesla clearly was using spheres while he was developing the Colorado Springs oscillator, but during his work there he made the discovery of toroids. Photographs of the Colorado Springs machine clearly shows a brass toroid as part of the antenna mast to prevent corona leakage and premature breakout from the top of the extra coil. As we examine photos and patents of the Wardenclyff machine he built on Long Island, it is clear that the entire tower was con- structed to carry the giant toroid terminal. I do not have verifiable information as to the exact size of this terminal, but it is easily over 50' in diameter. Probably closer to 75-100'. Toroids perform several functions as discharge terminals on Tesla coils. 1) They provide a large top capacitance. This top capacitance helps "cancel" the high inductance in the secondary coil (as the "C" cancels the "L" in an LC oscillator), and increases throughput in the system. This is a key to achieving dramatic increases in current output from a Tesla resonator. 2) Toroids break down at much higher voltages than other shapes. The donut shaped field distributes the charge density. Higher voltages must reached before electrical breakdown occurs. To the coiler this means longer, higher voltage spark. By swapping a toroid for a sphere and retuning the system you can obtain a 20-30% increase in spark lengths with no change to input power. 3) Toroids sever the coupling. This may be a controversial state- ment on my part. But from what I have seen, appears to be true. A sphere discharge terminal does not want to separate from the field flux interactions between the primary and secondary. The primary field flux wants to couple the sphere discharger into the system as if it were another turn of the secondary. The spark from the sphere discharger will frequently follow the lines of force created in the primary/secondary field flux, and seek to strike downwards and back to the primary. While this may be useful if you wish to visualize the size and shape of the field, it does nothing to increase your spark lengths. A large toroid on the other hand will establish a field identity that is separate from the primary/secondary field inter- action. Since the toroid field is established well above the top turns of the secondary is does not affect the coil performance or ability to process energy. It does however allow the spark to leave the system unaffected by the primary/secondary lines of force. This has the effect of allowing a clean getaway for the discharge and promotes those long strikes to the ground or other more distant objects. 4) Toriods also have the beneficial effect of dramatically lowering the frequency of the secondary coil. By loading a large toriod on a relatively small coil, a very low secondary frequency is reached. Low frequency in Tesla systems means long spark. This way a small coil can give big coil performance. Because of this ability of the toriod to reduce the secondary to low frequencies, it is important to have a very large primary available that can be tapped out to over 10-12 turns in order to regain the system tune. Larger cap- acitors may be added, but my experience shows that no additional power or capacitance is required to get big increases in spark production. 5) Toroids provide excellent corona shielding. This shielding prevents corona losses and breakdowns in the top turns of the secondary winding. 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. The first method, and my personal favorite, uses a ridged or "corrugated" black 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. 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 con- ductive 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. 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. 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. 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. 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 ************************************************************************** Mike McCarty quoting Richard Quick: > 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. I used a piece of corrugated drain tubing but instead of covering it with tape to smooth it I covered it with wallboard joint compound, baked it, and sanded it down. (I'm a use what ya got type of guy). I then shot some primer on it and covered it with 2 inch aluminum HVAC tape. I cut a disc of 1/8" aluminum for the center. Mike McCarty *************************************************************************** From: chip (Chip Atkinson) Subject: Another toroid construction method. Greetings, A couple of weeks ago I built a toroid for my new coil (that will be finished in 97 or so, given as much time as I have). I found a fairly cheap way of building it and it looks fairly decent. Materials: two aluminum pie pans. These are the type that are not foil, but are lighter in weight than something that you would buy for baking. Aluminum drier hose. Aluminum solder. I got this at a welding supply company for about $7.50 per pound. It takes a little skill to use, but works pretty well. Note: This stuff also sticks to copper, so you can make Cu-Al solder joints. Procedure: Solder the pie plates back to back so that they look like >-< in cross section. Form the drier hose into the toroid shape and test fit to ensure that the ends touch when wrapped around the V formed at the edge of the pie plate assembly. When everything looks good, start soldering the hose to the pie plates until you meet at the starting point. Then solder the ends of the hose together. In cross section, the finished toroid will look somewhat like this O>-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: 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 .. If all else fails... Throw another megavolt across it! ___ Blue Wave/QWK v2.12