Helpful Tips ProjectHome Ideas 4 Sale Swords Library . Suppliers Misc Jacobs Ladder 1/4 Wave TC Bi-Polar TC Magnifying TC SS TC Concentric Spheres Spark Gap Coil Winding Ice Spikes Info Wanted Forbidden Trailblazers Sartorius
Tesla
Coil
Helpful Tips Project
Updated Sep. 11, 2006 Bottom of Page
Send your comments & corrections with this Feedback Form. For issues not addressed here, try www.pupman.com, do a search &/or post the Q for all to consider. I'm attempting to make this a Quick Reference Guide with useful info on many aspects of the coiling art. Forgive me if I'm missing a footnote or two, I'll add them upon notification.
Ballasting/Current Limiting Marx Generator Info SSTC Theory, et. al.
Breakdown Voltages Materials - Misc Static Spark Gap - Setting
Capacitors Metal Spinning Toroids
Coil Form Coatings - High Q Photo Tips Transformers - New - Dr. R.
Coil Form Material - High Q Racing Sparks - Tracking Vacuum Info
Drill Bit Info RFI/EMI Filter Info Wardenclyffe RF Power
Epoxy Types & Sources Rogowski Coils White Board - More Stuff
Ground Plane - RF Safety Gap Across Xfr
Magnetic Field Msmt Secondary Adjustments
Mag Wire & Hi V Wire Sphere Capacitances
5-27-4 TL. I can use the field of a
toroid implemented in the Inca program to have an idea of what happens. Consider
a ring of wire, with wire diameter of 1 cm and varying major diameter. I list
below the breakdown voltages calculated by the program:
Major diameter:
1 cm: 15.0 kV (a ball with 1 cm of diameter)
2 cm: 22.6 kV
4 cm: 32.9 kV
10 cm: 50.0 kV
1 m: 95.2 kV
10 m: 133.8 kV
100 m: 169.8 kV
1000 m: 203.9 kV
The breakdown goes slowly to infinity as the radius of curvature (half of the
major diameter of the toroid) of the wire decreases.
A bunch of wires results in a larger effective diameter of the wire, and in
greater breakdown voltage. I can still use the program to evaluate this case.
Consider 4 wires with 1 cm of diameter disposed as a square with distance
between the centers of the wires of 4 cm. A ring of this "wire" with
distance from the center to the center of the inner wires of 10 cm is described
in the program as:
* Toroidal conductor with 4 wires
C1 wire 50 0.1 0.02 0.005 0 360
C2 wire 50 0.1 -0.02 0.005 0 360
C3 wire 50 0.14 0.02 0.005 0 360
C4 wire 50 0.14 -0.02 0.005 0 360
The breakdown voltage for this case results as 112.4 kV
For larger rings (also changing the distance from the center to the center of
the inner wires, that is approximately the radius of curvature of the composite
wire):
0.5 m: 181 kV (compare with 95.2 kV with 1 wire)
5 m: 288 kV (compare with 133.8 kV)
50 m: 385 kV (compare with 169.8 kV)
500 m: 478 kV (compare with 203.9 kV)
So, it's not difficult to keep transmission lines at very high potentials
without excessive corona at the wires. The most problematic areas are the middle
points between towers, where the radius of curvature is maximum, and the
suspension devices in the towers, where it's common to see corona rings.
Antonio Carlos M. de Queiroz.
Dielectric Strength of Some Gases
Coil Form Material - High Q Acrylic, polycarbonate (both expensive).
Envirotek Lite , from Dick Blick art materials, use two coats, it hardens quickly.
West System 105 epoxy and 206 hardener, very rugged, hardens to a nice shine, and it has a very good insulating property. Curing time varies with temperature, humidity, and thickness of application, but generally it takes less than an hour to become run proof, leave the form and coil on winder and let it spin until the coating has set up.
Humidity Measurements
Radio Shack, et. al., often has
hygrometers for cheap as they change models and physical configurations. Run of
the mill solid state sensors are good to a few %. Sensirion
http://www.sensirion.com/
was mailing out samples for their humidity sensor chip. For instance: The
SHT11 is a digital (2 wire) output single chip sensor module, fully calibrated
with digital 2-wire output. 0-100%, -40 to 120°C, fully immersible, accuracy +/-
3.5%RH, +/- 0.5°C @ 25°C, response time humidity sensor 4s. Jim L.
You can also do the wet bulb/dry bulb thing and look it up in a psychometric
chart. If you've got a thermometer with any sort of probe (i.e. a standard
alcohol thermometer or a cooking thermometer or an electronic thermometer with
the probe) and a wet shoelace, you're all set.
Poly-Thermaleze, Heavy Build, Armored, (APTZ). Thermal classification of 200, dielectric breakdown at room temp. of 11kV, and 7kV at 200C. This is the best of the dual insulation system magwire coatings. The first coating is a THEIC modified Polyester followed by a modified Polyamide Imide. Corona inception @580V per their data sheets.
Imideze, Heavy Build, (IMZ). Thermal class 240, dielectric breakdown at room temp. of 12kV, and 7kV at 220C. Multiple coats of this aromatic polyimide. Has the highest overload resistance, cut through resistance, and operating temp. classification of any wire Phelps-Dodge makes. Extraordinary thermal and chemical stability. Fay Elec. Corp. carries lots of stock in most all gauges and their prices are reasonable. Tel is 630-530-7500 in Illinois.
http://www.tyree.com.au/ Australia
Q. Is Imideze (ML) wire worth the extra cost? Has anybody experimented and verified that the theoretically lower dissipation factor increases output? Or is it a diminishing return, compared to HD Thermaleze? For that matter, are Teflon, Litz, or multi-filar secondary windings a perceptible improvement?
A. I use APTZ & IMZ and have no problems to report. Regarding any differences in performance, none that I can find. Is IMZ worth the extra money? I'd go with APTZ as a minimum, IMZ if you don't mind spending a few more bucks on a coil meant to last a few years. I've yet to wind identical coils with each type of coating and same wire gauge for comparison. John C.
A. Litz and stranded wires do little to improve performance. We tested Litz wire exhaustively against solid magnet wire and found very little difference in potential or current output of the sec. coil. Dr. R.
High Voltage Wire
I've found a source of high voltage wire that I thought I should pass along to those on the list. Princess Auto has insulated fence cable available at $14.99 CDN for a 50 foot spool. The ad states that it's rated at 20 KV and can be direct buried to run an electric fence bypass of a farm gate. Orders can be sent via phone at 1-800-665-8685 or online at www.princessauto.com. Weazle.
Metal Spinning http://www.coe.ufrj.br/~acmq/spinning/
Racing Sparks or Tracking problems on secondary coil
First determine that the windings are not dirty, scraped, burnt or otherwise damaged by carefully inspecting areas where the arcing has occurred, clean or repair as necessary, if possible.
If you're having tracking problems there is the definite possibility that your coefficient of coupling is too tight. With a 3-4 inch diameter coil usually the secondary starts 1.5 - 2 inches above the horizontal plane of the primary. With a 6 inch form the secondary rises to 3.5-4 inches above the primary plane. Inner turn of primary to coil form distance is 1.5 inches. These values produce consistent results without problems.
Another cause of tracking or "racing sparks" is using too small of a HV terminal. A small terminal cannot provide electrostatic protection of the coil and tracking problems begin to occur.
Slope of primary coil too steep.
Tesla List Discussion - 8-19-05
Original poster: "David Rieben" <drieben@midsouth.rr.com>
Dr. Res, all,
Also, too much dust on the form can cause the racing spark conditions. I've had this happen to me with one of my large coils of the past. It had been stored for a while in dusty conditions and the racing sparks started as soon as I fired it up. At first I couldn't figure out why it was doing this as it had never given this kind of problem before. After dusting the secondary form and cleaning it up nicely, the problem disappeared.
David Rieben
----- Original Message ----- From: "Tesla list" <tesla@pupman.com>
To: <tesla@pupman.com>
Sent: Thursday, August 18, 2005 6:19 PM
Subject: Re: Tesla Coil - Internal Arcing on Secondary
>Original poster: "D.C. Cox" <resonance@jvlnet.com>
>It can also happen if you handle the coilform or coil with your bare hands especially if you are a "sweaty palms" type of person. The sodium chloride in your skin oils is an excellent conductor. After we wind a coil, especially a magnet wire type coil, we always use gloves to handle it. At 200-300 kV or more skin oil will track all over the coil --- not always but usually when you don't want this kind of problem.
>Dr. Resonance
>
> > The secondary wire itself should not be arcing to the form. There is no reason for this to happen.
>>If you get grease on the form, it will happen.
Safety Gap Across xfr - Setting
Original Q: How do I determine the gap distance for a safety gap on my transformer?
"Daniel B., Matt D." With the gap directly across the transformer as Matt describes, start with the gap open (no arc) and then adjust the gap closer until an arc is struck. Turn it off, open the gap just a bit more and you're done. This is your critical safety gap upper limit. Your main spark gap can be set as wide as possible to give consistent operation without exceeding this number. In the case of a multi-gap, the sum of all the individual gaps must not exceed this limit. If you're into resonant rise or other run-to-destruction fetishes, then all bets are off. Just go for it and use a little less gap on your next transformer.
Always bring power up with a variac.
Never adjust a gap while it is firing.
Your NST secondary is a 2-terminal circuit, one of them being the case. Using a simple 2-electrode safety gap between the HV bushing and the case is all that's required. Regards, Gary L.
Original Q: "Chris F." My question is, how does one determine what width of spark gap is needed? Is there a specific guideline, such as so many mm per kilovolt? This is for an air-cooled static gap with several gaps in series.
Answers:
For an AC powered coil, I have found a reasonable first approximation to be 0.5 mm/kV of rated (rms) transformer output. The precise mm/kV is difficult to predict. It is dependent on temperature, humidity, cleanliness and geometry of electrodes, altitude, barometric pressure, smog level, (and often moon-phase, planet alignment, size of audience, etc.) - Matt D.
A good starting point is 30 kV/cm for a uniform gap - Jim L.
On your upper base assembly
add a small drilled and tapped 1" x 1" x 3/8" thick piece of
brass. The sec. coil should also have a brass stud on it's base so it will
screw into the brass plate. A small separate hole is drilled and tapped for
ground wire attachment.
Make the stud on your sec coil extra long, like 2" to 3" long.
Now you can slip a tight piece of thick wall tygon tubing around it, gently
bend the tubing 90 degrees, and slip the other end over a variable slow speed
elec. drill or small DC gear motor.
This will allow you to run the sec coil up and down while it's running so you
can see the dramatic effects of coeff. of coupling adjustment to spark output.
After you do this with your proposed 8 inch coil please report back to the
list the results of your experiments. I'm betting with an 8 inch dia. coil
you will require an elevation of around 5 inches (first lower turn to sec to
horizontal plane of primary measurement). Let us know your results.
Other experimenters may wish to try this with their 4, 6, 10, 12, 16"
coil forms.
We make a lot of 18 inch dia. coils and found 7 inches to be the most
effective coeff. of coupling. For our 24" diameter coils it requires 9"
for best performance.
Most experimenters way over-couple their coils and lose performance that they
are not even aware is available. Happy coiling, Dr. R.
Custom Tesla transformers - contact Dr. Resonance, he's designed a 16kV, 250mA neon type transformer, these have current limiting with shunts so the external reactor can be omitted and it will surely be without that wonderful asphalt or epoxy potting. Three of these bad boys and you've got 12kVA to play with. They're being made in the U.S. and should be available by August or September, 2004.
Neon - N. Glantz & Son, Anaheim, CA (800) 273-1878, Fax (714) 634-8657. They offer a 3 year, no questions asked, warranty. Note that the warranty is calculated forward from the date code on the transformer (normally not over six months old at time of purchase).
De-potting electronic NST's - What type of solvent would dissolve the high voltage potting in the electronic NST's? I've tried soaking it in acetone, but it only melted the plastic shell. Answer: Methylene chloride should do the trick. You should read some safety data first: http://www.osha.gov/SLTC/methylenechloride/. And don't let it soak longer than necessary, it could dissolve the component bodies as well. I find that regular (twice daily) removal of the softened potting compound helps speed things along. Tom L. Available from: Columbus Chemical Industries, Columbus, WI. tel. 920-623-2140. 1 & 2 liter cans.
De-potting asphalt NST's
- Heat in oven until the asphalt can be poured out of the
metal case, clean out as much as possible and remove from case and place in
sealed container of gasoline. Leave it soaking for a day or two and then
get out some small brushes and start the final cleaning. Total disassembly
and reassembly may be required, keep the plates in order and maybe leave out a
few of the 'I' shaped shunts when re-assembling an 'E' core (on a Franceformer
15kV, 60mA, I left out 7 of the shunts).
"The trouble is not that the world is full of fools, it's just that lightning isn't distributed right." - Mark Twain
"Invention is the most important product of man's creative brain. The ultimate purpose is the complete mastery of mind over the material world, the harnessing of human nature to human needs." - N. Tesla
