Re: Coil Form needed

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com> 


Paul

If you are in the initial design phase and have up to 25 kVA available, it
would be in your best interest to use a coilform with a dia. between 24 and
36 inches.  This allows a higher inductance ratio due to the "radius
squared" factor and will give you very large sparks --- up to 22 ft.  I
recommend a 4.5:1 height/dia. ratio to prevent flashovers.  With this large
dia. sec you need to start the first turn approx 8.5 inches above the
horizontal plane of the primary coil for most efficient coeff. of coupling.

You will need a large toroid, around 6 ft. dia x 24 inch cross section, but
these are easy to make with styrofoam sheets and chicken wire mesh.  Look at
the Dallas/Ft. Worth DFWTCB Tesla Coil Builders group for their excellent
toroid.

While magnet wire can be used in a large coil I would recommend 16 AWG MIL-D
(3 kV PVC) wire for the winding job.  It's 3 kV working rating and around 20
kV/turn breakdown offers excellent performance and protection on large
coils.

We can supply fiberglass (extren) tubes in 18 inch dia. and 24 inch dia. for
your project.  Contact us offlist or tel us at 608-356-3647.  Be sure to
seal the tube inside and outside (after sanding) with at least 3 coats of
G.E. Red Glyptal.  With the 3 kV MIL D wire you only need a single coat of
clear Glyptal on the wire as a final coat.
The wire's dielectric does the insulating ---- you are just sealing it from
moisture adhesion to prevent HV RF tracking.

Have fun.

Dr. Resonance

 >  >
 >  > I am looking for a coil form 12" or greater diameter. The length
 >  > should be
 >  > about 4 times the diameter. Also I am planning on using a 40kV
 >  > .5uF
 >  > capacitor for the tank circuit. I have a 25kVA pig to drive it.
 >  > Has anyone
 >  > on the list ever used that much capacitance in their tank circuit ?
 >  >
 >  >
 >  >
 >  > Paul S. Marshall
 >
 > Paul,
 >
 > I would think that 0.5 uFD would be way too large for
 > anything except maybe for an Electrum sized coil. The
 > biggest cap that I've used so far is .0825 uFD, but I
 > do now have (2) 0.1 uFD, 50 kV Hipotronics custom Tes-
 > la caps that I got from Jeff Parrise of KVA Effects.
 > I plan on using one of these for my future BIG coil
 > project and driving it with a 15 kVA pig.
 >
 > As for large diametered secondary coil forms, I was
 > able to get gray PVC ducting pipe from a local plas-
 > tics supplier. I had picked 12" but they had 18" too.
 > Of course it was quite pricey, though. I payed over $5
 > a foot for the 12" and I'd hate to even ask how much
 > the 18" was ;^0 Another cheaper alternative is the
 > concrete former tubes. They are cardboard and are
 > considered to not be the best form material due to
 > higher lossiness and low Q, but if thuroughly dried
 > and varnished, they do work. I know from experience.
 > My biggest coil to date used a 12" dia cardboard
 > "Quiktube" concrete fromer from Home Depot and it
 > was only about 38.5" long but gave 8 to 10 ft. sparks
 > from a 9x30 toroid and driven by a 10 kVA pig (14.4 kV)
 > and with the aforementioned .0825 uFD primary capa-
 > citance and a homemade lexan and brass RSG.
 > I've seen 24" concrete formers at construction sites
 > so you could definitely build a large coil with one
 > of these.
 >
 > David Rieben
 >
 >
 >
 >