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Re: Tesla coil Parts and plans
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- Subject: Re: Tesla coil Parts and plans
- From: "Tesla list" <tesla@xxxxxxxxxx>
- Date: Tue, 22 Mar 2005 08:07:46 -0700
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Original poster: "Dr. Resonance" <resonance@xxxxxxxxxx>
Best cap size is C = 1.57 x Cresonant value .009 to .01 uF works good with
a 30 mA xmfr.
Centerline of toroid is 5 inches above the last winding on the sec coil.
> > I have been scrounging parts to build a SGTC and so far I have: 15 kv
> 30 mA
> > NST, 3 lbs. of 26 AWG and 9 lbs. of 25 AWG magnet wire, a 8 ft x 4
> > piece of thin wall white PVC (not foam core), a 0 - 140 v 20 A variac,
> > length of 3 inch diameter flexible dryer duct formed into a toroid
> with 2
> > pie plates forming the center, 50 ft. of .25 inch soft copper tubing,
> > .003 mF 35 kv film caps, two .03 mF 35 kv pulse discharge caps, 4 680
> pF 20
> > kv door knob caps, 2 .01 mF 40 kv poly caps, eight 5 kv 2 A diodes,
> an 8
> > ft copper clad ground rod, and a 4 series gap made with 1.5 inch hard
> > copper pipe inside a 5 inch piece of PVC with a cap that allows me to
> > connect the shop vac to the top and suck fresh air through the spark
> Your .03/35kV caps sound like the Maxwell units sold on eBay, and they
> should be OK. I couldn't comment on your .01/40kV or .003/35kV units
> without knowing a good deal more about them. The doorknob caps are good
> for an R-C filter between the main gap and NST. After things are tuned
> well, you may find that you can use something thicker than a 3x??
> > I also have Wintesla, Walt Noon's designer software, and JavaTC 9.1.
> > all give very similar results, which is reassuring. I still have 1001
> > questions. My knowledge of electronics is virtually all self taught
> and I
> > worry that I am guilty of some misconceptions. Also, I am extremely
> > conservative and I want to build in as many protective features, both
> > safety and protection of the coil itself.
> > Before describing my plans for the controls, tank circuit, and
> primary, I'd
> > like to get the secondary out of the way. I have cut off 21 inch
> length of
> > 4 inch diameter PVC and sanded off all imperfections and ink. I then
> > it with multiple coats of polyurethane, inside and out. The following
> > have been a mistake. I covered all the area to be wound with wire with
> > double sided carpet tape to help hold the winds as I apply them. I
> want to
> > use the 26 AWG magnet wire and wind 18 inches. I have calculated that
> I can
> > get approximately 1000 winds. I also plan to seal both the top and
> > of the secondary and provide a small hole in the bottom to equalize
> > pressure. I plan to leave 1 inch of PVC uncovered by wire at the
> bottom and
> > 2 inches at the top. How much space between the top of the secondary
> > and my toroid?
> The use of carpet tape is a new one and if it's clear, odds are that
> it's not a problem, but I still wouldn't bet the farm on it. I
> personally would have put a few more turns, out to at least 21", but
> nothing is cast in stone here. The lowermost extent of the toroid
> should generally be no more than 1-2 inches above the top turn.
> > Starting at the wall plug, I want to put an EMI filter between the
> > outlet and the variac. My first stupid question. My variac says that
> > side is common to line and load. Does this mean that the variac is NOT
> > acting as an isolation transformer?
> Absolutely - it is not isolated. You should look at the wiring; the
> neutral is common to input and output.
> > Do I ground the variac case to my house ground?
> Yes, and that's the only thing, with the possible exception of an EMI
> filter case, that goes go to house ground.
> > From the variac, I plan to go to the NST. Where do I ground the
> > NST, house ground or to the RF ground?
> RF ground, although some may differ.
> > From the NST, I want to wire to a
> > safety gap with the center grounded to my RF ground. Should I provide
> > bypass cap between the NST and safety gap? Which caps are suitable for
> > this? Do I want to put in RF chokes between the safety gap and main
> > capacitor?
> Use an R-C filter. Chokes used to be thought to be effective, but more
> recent research shows that they do more harm than good. See my web site
> at http://www.laushaus.com/tesla/protection.htm for the filter circuit.
> > Any recommendations on which of the caps to use that I already
> > have? The software recommends approximately .006 mF cap for the
> > The Java software recommends using a larger cap than is recommended by
> > program. Here is where I think I am a little fuzzy.
> The software is computing the mains-resonant value - the value that
> would resonate at 60 Hz with your NST's secondary. This was at one time
> thought to be the value that would extract the most power from the NST.
> This value will work, but it turns out that there's nothing magical or
> particularly sweet about it. I've found that a value of 2 times the
> mains resonant value (when using static gaps) worked best for me. I
> would try using your two .03uF caps in series for .015uF, or your .01uF
> cap, if it is in fact TC-worthy.
> > How is the value of the
> > primary cap determined? What is the impact of using a larger than
> > cap? Does the size of the cap, the distance between gaps in the spark
> > the inductance of the primary coil and the size of the toroid all
> > this calculation? Won't any of these factors change the resonant
> The cap size is generally chosen by sizing it according to the power
> supply - by choosing some multiple (1.5 to 2.0) of the mains-resonant
> value. The secondary and top load sizes are also chosen based on the
> power supply size, although there is no simple or agreed upon formula
> here. Mostly just experience and what "looks right". Then the primary
> inductance is chosen to bring the primary and loaded secondary
> frequencies to the same value. The main gap width is strictly a
> function of the power supply voltage, and has no bearing on frequency of
> > Next, I want to wire to the series spark gap. How do I determine the
> > of each individual gap? At what total gap should I start at? Will too
> > of a spark gap cause excessive load on the NST? I had trouble getting
> > NST and I paid too much for it. I want to do everything I can, within
> > reason, to protect it!!!
> The ONLY way to set a static gap is to wire it across the NST at maximum
> variac, and set it to it just barely fire. The caps must be out of the
> circuit for this adjustment. For a ballpark figure you can use 0.25"
> total gap width for a 15kV power supply, but the exact figure will be a
> function of the gap geometry, airflow, air pressure, electrode
> temperature, texture, number of gap segments... Many variables. Too
> wide of a gap will permit excessive voltage on the caps and NST - FAR
> higher than the NST secondary rating - and this is why so many new
> builders fry their NST's. Performance will always be much better with a
> wider gap, and it will be very short lived.
> > What type of wire should I be using to wire from the NST to the bypass
> > to the safety gap to the cap to the series SG and then to the primary
> > I was planning to form the primary with a 6 inch diameter. One inch
> > the inner winding and the base of the secondary coil. Is this
> > spacing? I plan to space .25 inch between windings. I calculate that I
> > get between 13 and 15 windings. To attach to the primary, I plan to
> > my wire to an ATC fuse holder and then snap the fuse holder onto the
> > tubing wherever I like.
> The wiring from the NST to the safety gap to the main gap carries only a
> small current, so any size will do. The loop consisting of the primary
> coil, main gap, and tank cap should be short, direct, and heavy. For
> use with a 15/30 NST, probably anything 14gauge or heavier will do.
> > I am going to great lengths to build a substantial RF ground
> > separate from my electrical service and water pipes. The ground here
> > very good for grounding, red clay with a high iron content. I plan to
> > at least 5 eight foot ground rods with 4 of them forming a square 5
> feet to
> > the side and cabled to each other and then cabled each to a central
> > which will be my attachment point for RF ground. This attachment point
> > be approximately 10 feet from the TC location in the front of the
> garage. I
> > plan to use two 4 AWG car jumper cables, 4 strands total to attach the
> > to ground.
> Your ground will be far better than most ;-)
> > I plan to attach the NST case, the safety spark gap, and the base of
> > secondary all to RF ground. Can someone please explain to me
> everything I
> > need to know and am afraid to ask about a counterpoise ground?
> With a ground that good I don't think you need a counterpoise. I've
> never used one.
> > Any and all comments will be most gratefully accepted. If I seem to be
> > particularly off base in any area, please point it out. I am striving
> > learn as much as I possibly can while doing this, instead of just
> > someone's recipe. Oh yes, I almost forgot. I was contemplating using
> the HV
> > diodes I have to rectify the NST output to pulsed DC. Would this help
> > ease the burden on the primary cap?
> I would skip the diodes. The stress on the caps comes not from the 60
> Hz stuff, but from the tank frequency oscillations.
> > If anyone would like to communicate with me offline about this, please
> > My email is pbbrodie@xxxxxxxxxxxxx
> > Think positive!
> Regards, Gary Lau
> MA, USA