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Tesla Coil Builder 3/?

 * Original msg to: Cwolins-at-orion.it.luc.edu
 * Carbons sent to: usa-tesla-at-usa-dot-net


                 Toroid Discharge Terminals

Another feature of the "classic" Tesla coil design that is in 
need of retirement 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" can-
cels the "L" in an LC oscillator), and increases the throughput in 
the system. This is a key to achieving dramatic increases in current 
output from a Tesla resonator. I will mention here that adding a 
large toroid will require a solid RF ground on the base of the coil
to handle the increased throughput and current. 

2) Toroids break down at much higher voltages than other shapes.
The donut shaped field distributes the charge density. Higher
voltages must be 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 a 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 it does not detrimentally 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 lateral strikes that 
then reach the ground or other more distant objects.

4) Toroids also have the beneficial effect of dramatically lowering 
the frequency of the secondary coil. By loading a large toroid 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 
toroid 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 toroid 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 toroid ran me over 350 clams. My ten inch secon-
dary 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 (usd) 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 toroids 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 diam. 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 toroid 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. In place of this, a disk of aluminum sheet may be 
cut to fit and mounted into place for the center plate. This 
eliminates the need for the spray adhesive and foil covering. 

This basically completes the construction of this type of
homemade toroid. 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 toroid 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 toroid 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 toroid will function perfectly even if 
all sections are not perfectly electrically bonded.

In practice a homemade toroid 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 toroid
costing hundreds of dollars, though typically homemade toroids 
do not have the "polish" that commercial toroids 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

*************************************************************************
Quoting Ed Sonderman:

If you only need a small toroid you might look at a styrofoam core.  
The first toroid I built was made from two styrofoam rings or donuts 
that you can buy from a hobby or craft store.  They are for making 
decorative wreaths like for Christmas.  I bought two that were 14.0" 
in diameter and about 2.0" thick.  Then I cut a piece of acrylic in 
a circle of about 13.0" and placed it between the two styrofoam rings 
and used clear shipping tape to fasten it all together.  Then I covered 
it with aluminum foil tape.  It only took about an hour or two and cost 
probably less than $20.00 (usd).

**************************************************************************
Quoting Mike McCarty:

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
***************************************************************************
Quoting Chip Atkinson:

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>-<O  

Notes:  The aluminum solder melts at a fairly high temperature, so you 
should experiment on something expendable first.  I can use lead-tin 
solder just fine, but this stuff is a challenge (but worth it). 

Chip
**************************************************************************
Quoting 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" diam 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" diam PVC pipe of the height 
desired (I am using about 6.0" now).  Do not glue it.  Then I take an-
other 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 toroids all have a 1/4" diam hole drilled through the center.  I set 
the toroid 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 toroid 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 
toroids.  Which I never thought would be a problem but now I have three.

I now wish I would have gone with 2.0" diam  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)

My newest toroid is made of 5.0" diameter 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

- Area: UUCPE-Mail -----------------------------------------------------------
  Msg#: 1216            Pvt                          Date: 12-12-95  02:02
  From: Marcusy-at-ozemail-dot-com.au                       Read: Yes    Replied: No 
    To: Richard Quick                                Mark:                     
  Subj: Re: Toroid Dischargers
------------------------------------------------------------------------------
From: Marcus Young <marcusy-at-OZEMAIL.COM.AU>
To: Multiple recipients of list USA-TESLA <USA-TESLA-at-USA.NET>
Date:         Tue, 12 Dec 1995 01:02:30 -0600
Subject:      Re: Toroid Dischargers

Richard and Tesloids,

At 12:57 AM 12/11/95 GMT, you wrote:
> * Original msg to: Hook-at-vitinc-dot-com

>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 toroid 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. In place of this, a disk of aluminum sheet may be
>cut to fit and mounted into place for the center plate. This
>eliminates the need for the spray adhesive and foil covering.

To add to list of toroid forms, using a life-bouy as a form with
the Al tape method should produce a toroid just about as smooth
and flawless as the expensive commercial types you mentioned.
They are light and hard, and an ideal size for high power coils!
I think a second hand one would ony cost a few dollars.

Just an idea.  :)

Marcus
*******************************************************************************

Quoting  Se-crawshaw-at-wpg.uwe.ac.uk:

Re: constructing toroids.

I recently made a 12" x 3" toroid from four 3" stainless steel
pipe elbows (quadrant sections). These were welded together, then
ground smooth and finally shotblasted after brazing a circular
steel plate into the middle for support. This assembly looks
**smart** although it does weigh quite a bit. If you have access
to welders and large sections of pipe, this could be a good
method for making a "professional " toroid terminal.

steve

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