Toroid Sizing

Quoting Ed Sonderman:

 ES> My secondary is built on a 6.0" dia pvc pipe - probably      
 ES> 6.25" od.  It is covered with 5 - 6 coats of polyurethane.   
 ES> Toroid is 40" in dia and 5 or 6" thick.    
 RQ> I can help a bit here as I assisted with some design details
 RQ> during the step by step peaking of the system. 

Quoting Alan Jones:

 AJ> I have a question about this large toroid being used. Is it    
 AJ> made out of  something like stovepipe flue or something       
 AJ> else? And how do you support this  thing? It sounds bulky.    

These toroids are actually very light. The coil form typically 
extends an inch or so above the secondary winding and the coil
form is capped with plastic plates that are epoxied to both ends 
of the form. A stand off insulator may then be placed (or glued) 
on the end cap to hold the toroid up off of the coil. Ed made a 
system whereby PVC plastic pipe lengths are replaceable for different 
height standoff insulators. The following came from the archives:


Quoting Rodney Davies:

 RD> I had a 12" diam copper ball, but it was severely damaged,   
 RD> I'm in the process of getting an aluminum toroid made (just  
 RD> a bit bigger than the  diameter of the primary)...but I      
 RD> wouldn't have the faintest idea as to how they are made, and 
 RD> the methods you spin them...  You know your toroid on your   
 RD> 10" coil, is it just one piece of like sheet aluminum spun   
 RD> into a dohnut, or is it in two halves?  I need to know       
 RD> everything about them???

This is a good subject to expound on. There have been 
a few questions recently about toroid construction.

I have two commercially manufactured spun aluminum toroids. They
are quite expensive. These commercial toroids are spun out of two
separate plates of aluminum which are then TIG welded together
around the outside edge. The toroid is then given to the grinder
who grinds and machines the weld to make an invisible smooth
seam. Prices for the smallest commercial toroids start around 100
dollars US currency. The scanned photo of my 10 inch diameter
coil shows a 20 inch diameter by 5 inch cross-section commercial
spun aluminum toroid. This 20 x 5 toroid cost $325.00 US.

To max out my 10 inch diameter secondary coil I figured I would
need a 40+ inch diameter toroid. The price for a commercial spun
aluminum toroid in this size range was priced at over $2000.00
US! Needless to say I did not purchase this essential component.
BTW, most coilers find that two or three toroids of different
sizes are essential to their experiments.

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

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 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.

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 be 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

Richard Quick