Re: Tesla coil Parts and plans

["Tesla list" <tesla@xxxxxxxxxx>]

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
>
>
>