Re: A few questions about coil designing

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

Original poster: DRIEBEN-at-midsouth.rr-dot-com 

Hi Robert,

Not quite sure that I follow you on this :^/ In a previous big
coil that I built, I used a .083 uFd cap with a 12 1/2" diame-
ter secondary that was wound with #16 wire and only had about
660 turns (~38" long) and topped with a spun 9x30 Landgren to-
roid. I was able to tune it in with about 7 turns on the spi-
ralled primary coil. >1000 turns may be desirable or preferred
but is certainly not essential for the secondary, especially
with larger diametered secondaries in larger coils since the
large diameter gives much more L per turn. Doesn't L increase
as the square of the coil's radius?

David Rieben

----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
Date: Friday, November 19, 2004 12:14 pm
Subject: Re: A few questions about  coil designing

 > Original poster: "robert heidlebaugh"
 > <rheidlebaugh-at-desertgate-dot-com>
 >
 > David: Just a quick responce. Your secondary is only 897 turns not
 > 1500turns so it will resonate at a high frequency. Your capacitor
 > is o.1 ufd
 > over twice the value neaded for 1500 turns so your primary will be
 > way to
 > low. Even if you use both your capacitors in series you may still
 > have more
 > capacitance than neaded for your low turn secondary.
 >      Robert   H
 > --
 >
 >
 > > From: "Tesla list" <tesla-at-pupman-dot-com>
 > > Date: Thu, 18 Nov 2004 21:02:14 -0700
 > > To: tesla-at-pupman-dot-com
 > > Subject: A few questions about  coil designing
 > > Resent-From: tesla-at-pupman-dot-com
 > > Resent-Date: Thu, 18 Nov 2004 21:04:24 -0700
 > >
 > > Original poster: "David Rieben" <drieben-at-midsouth.rr-dot-com>
 > >
 > > Hi All,
 > >
 > > I am in the process of constructing a fairly big coil with a 12
 > 3/4" x
 > > 44" long secondary wound with 897 turns of #17 heavy build Essex
 > > magnet wire. That makes for just over 3000 feet of wire.
 > > The primary is 12 spiralled turns of 5/8" OD soft copper
 > > tubing with the outer most turn at nearly 40" diameter. There
 > is an
 > > approximate 1/2" spacing between each primary turn.
 > >
 > > For the primary capacitor I will be using either one or two
 > paralleled > .1 uFd, 50 kV Hipotronics commercial pulse
 > capacitor(s). These are
 > > Tesla coil specific custom capacitors that Jeff Parisse was
 > using for his
 > > Model 10 coil. I'm thinking that .1 uFd will be sufficient primary
 > > capacitance for my design.?
 > >
 > > The power supply will be either a 10 or 15 kVA, 14,400 volt
 > pole trans-
 > > former (have one of each), controlled and ballasted with (2)
 > paralleled
 > 1256D
 > > Powerstats and a Lincoln 225 amp arc welder core set for the
 > maximum welding
 > > amperage. The arc welder's core guts have removed from the
 > factory steel
 > > box and placed in a tank of transformer oil to increase the
 > duty cycle.
 > >
 > > The rotary gap will most likely be ASYNCH G-10 and tungsten
 > > with a variable speed DC or universal drive motor. I may have to
 > > break down and pay someone to do this part for me as i am
 > > no machinist and I do want it to be right :^))))
 > > I have designed and built big coils before but I want to make sure
 > > that I get this one right the FIRST time ;^)
 > >
 > > My questions are: Will there be a problem of turn/turn flashover
 > > on the outer turns of the primary coil since there is often
 > less than
 > > 1/2" spacing between the adjacent turns? If it's tapped at say
 > the 7th
 > > turn then there's 5 additional unused turns that can develop an
 > auto-
 > > transformer effect. I may just remove most of the unused turns if
 > > this proves to be a problem once tuned in.
 > >
 > > Also, my Hipotronics pulse caps are the single bushing, steel
 > > can type with the steel case grounded to the terminal opposite
 > > of the bushing. I'm thinking that I'll need to place the capacitor
 > > in parallel with the transformer instead of the spark gap in
 > paral-
 > > lel with the same, otherwise I'll end up with the entire exterior
 > > case of the capactior floating at 14,400 volts ;^O. I've heard that
 > > this wiring variation of the primary circuit places more strain on
 > > the transformer but since I'm using a pole transformer, I don't
 > feel > that this will be an issue in this case.
 > >
 > > I plan on building a 12" minor diameter toroid from aluminum
 > flex-
 > > duct tubing from McMaster-Carr, with a major diameter of 48" to
 > > 54". I'll probably also use a smaller toroid (4" minor diameter x
 > > 16 to 20" major diameter) for a corona shield of the topmost
 > > turns of the secondary. With a toroid this large, will .1 uFd be
 > > sufficiently large for the primary capacitor? It seems that my
 > > power supply combo may not have suffiecient power to drive
 > > .2 uFd of primary capacitance. Any comments welcome ;^)
 > >
 > > David Rieben
 > >
 > >
 >
 >
 >