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Re: My 8" secondary

In a message dated 11/17/98 8:20:53 AM Pacific Standard Time, tesla-at-pupman-dot-com
writes:

<< 
 Thanks for the kind words from a professional coiler. If it works as good as
 it looks (pictures will be available on my website some time end of the
month)
 I will be happy. A 8"x 50" toroid would be really HUGE (whew !!). I donīt
know
 if I can find AL dryer duct hose with a 21 cm diameter. I would hate to use
 plastic stuff and wrap it with aluminum (doesnīt look very pretty) foil or
 tape.
 
 I was planning on powering the coil with 6 NSTīs (voltage matched, in
 parallel) Total current would be around 600mA, but due to german law, only at
 a relatively low voltage (7.5kV; 10.6kV PtP). If this doesnīt work, I will
 rewind an old 8kVA welder transformer (Iīve already taken it apart, started
 making new wire formers, etc) for high voltage (Input: 380V (across two
 phases: keeps the input current low) // Output:12-15kV-at-300-500mA). 
 
 For starters I planned on using a multiple static gap made from 6-7 pieces
 (5-6 gaps) of 35mm (1.3") copper pipe each about 4-5" long. Maybe two of
these
 in parallel to keep the heating effects down to a minimum. I also plan on
 building a SRSG sometime in the future.
 
 My capacitors will be homemade rolled PE type. I asked Siemens over here what
 a 0.1uF 30kV ceramic cap would cost and they told me depending on end design
 somewhere around $2500-$3000. (Yes thats $$īs, not DMīs. Theyīre crazy !!!
 Esp. if the cap goes poof after a few seconds of operation). I was thinking
of
 using somewhere between 50-100nF for this coil. A mains reso cap would be too
 big (somewhere around 254 nF) and as I have 4.5kVA input power at my
disposal,
 I donīt think it would be necessary. With 50-100nF I should be able to up the
 break rate to 400-500 BPS (later with the RSG) and still be able to fully
 charge it with my NST psu. Oil used will be either Shell Diala-X or castor
 oil. Castor has a much higher K value (4.5), but Iīm not sure how long castor
 oil will "last" as it oxidizes when in comes in contact with air. 
 
 Malcom told me he had designed a 100nF cap for his 9.9" coil: 
 Malcom wrote:
 "Details of construction are online on Jim Fosse's homepage. There are 
 (from memory) 12 plates, each 1 metre long. Dielectric between the 
 plates consists of 2 layers of 0.25mm polyethylene. A 12 metre long 
 roll of cooking foil just does the job."
 
 I would be interested in having a look at Jimīs site. Anyone know his web
URL?
 Jim: Are you out there? 
 
 The only thing which "bothers" me is the very small (0.5mm=19.68 mils)
 dielectric distance. I was thinking of somewhere around 48-55 mils for my
 7.5kV input to play it safe. However, I donīt know  what voltage Malcom was
 using to power his coil.
 
 BTW: Does anyone have a formula that allows you to calculate the physical
size
 (diameter) of a rolled cap (given total thickness of everything before
 rolling)?
 
 What I am not sure of yet is the primary coil design. A helical coil will
give
 me too much coupling, plus it would invite flashover (unless I build a
monster
 primary size-wise). However, I donīt know if I should go for a conical
primary
 (low angle, say 15°) or a flat primary. I donīt know if the flat primary
would
 give me enough coupling. A conical coil would be a little harder to wind (as
 it is supposed to perfrom well AND look good)
 
 My RF ground consists of 4 pieces of 40mm galvanized (1/8+" thick) T-iron
 (each about 4+ ft long). I smacked these about 4 ft apart into the soil (all
 except the last one, which is 2" out of the soil) about 8" under the sod
level
 (with ease) and interconnected them with 10mm^2 wire. From the RF ground to
 the coil I run 16mm^2 flexible welding cable. I think this ground should be
 "ground"-able enough.
 
 Coiler greets from germany,
 Reinhard 
  
 << 
   BTW: I just finished my 8" secondary:
   
   Coiler greets from Germany,
   Reinhard >>

Reinhard,

I would guess that you will test and tune the new coil with less than the full
600 ma and then add more transformers as you get things tuned in.  You will
reach a point where a static gap will not quench and I would guess that would
be around 200 to 300ma.  This is based on my experience at 14 kv and not sure
how much effect your lower voltage will have on this.  You will need a rotary
gap eventually.

Your estimate of .05 uf to .10 uf I think is right on for an 8" secondary.

My advice on your primary design would be to wind it flat using 3/8" or more
likely 1/2" diameter tubing.  Allow cutouts on the platform that you mount it
on for the tap to come up from under the primary.  I originally built my
primary in a 30 degree saucer shape and have recently rebuilt it in a flat
design.  You won't have any problem getting plenty of coupling.  My secondary
is mounted so that the lowest winding is about even with the primary.  I have
spacers made so I can raise the secondary if necessary to reduce coupling and
could always raise the primary to increase coupling.

My toroids (5" x 30" and 5" x 40") are both made from flexible corrugated pvc
drain pipe.  They are first wrapped with clear packaging tape then wrapped
with aluminum foil tape.  They are not perfectly smooth by far, but look good
and work fine.

Ed Sonderman

Ed Sonderman