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Re: Tesla coil Parts and plans

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.

Dr. Resonance

> > > > 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 > inch > > piece of thin wall white PVC (not foam core), a 0 - 140 v 20 A variac, > a > > 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, > 50 > > .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 > gap. > > 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?? > toroid. > > > I also have Wintesla, Walt Noon's designer software, and JavaTC 9.1. > They > > 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 > for > > 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 > sealed > > it with multiple coats of polyurethane, inside and out. The following > may > > 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 > bottom > > 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 > coil > > 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 > wall > > outlet and the variac. My first stupid question. My variac says that > one > > 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 > a > > 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 > primary. > > The Java software recommends using a larger cap than is recommended by > the > > 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 > necessary > > cap? Does the size of the cap, the distance between gaps in the spark > gap, > > the inductance of the primary coil and the size of the toroid all > impact > > this calculation? Won't any of these factors change the resonant > frequency? > > 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 > anything. > > > Next, I want to wire to the series spark gap. How do I determine the > width > > of each individual gap? At what total gap should I start at? Will too > wide > > of a spark gap cause excessive load on the NST? I had trouble getting > this > > 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 > cap > > to the safety gap to the cap to the series SG and then to the primary > coil? > > I was planning to form the primary with a 6 inch diameter. One inch > between > > the inner winding and the base of the secondary coil. Is this > sufficient > > spacing? I plan to space .25 inch between windings. I calculate that I > will > > get between 13 and 15 windings. To attach to the primary, I plan to > solder > > my wire to an ATC fuse holder and then snap the fuse holder onto the > copper > > 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 > completely > > separate from my electrical service and water pipes. The ground here > is > > very good for grounding, red clay with a high iron content. I plan to > sink > > 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 > rod > > which will be my attachment point for RF ground. This attachment point > will > > 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 > coil > > 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 > the > > 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 > to > > learn as much as I possibly can while doing this, instead of just > following > > 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 > to > > 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 > do. > > My email is pbbrodie@xxxxxxxxxxxxx > > Think positive! > > Regards, Gary Lau > MA, USA > > >