[TCML] Fixing up an old coil -- tune-up suggestions
Anthony R. Mollner
penny831 at earthlink.net
Tue Nov 13 20:07:46 MST 2007
I liked the list the way it used to be because now it's more difficult to
sort out spam from the GOOD tesla coil e-mail.
From: tesla-bounces at pupman.com [mailto:tesla-bounces at pupman.com]On
Behalf Of huil888
Sent: Tuesday, November 13, 2007 6:39 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Fixing up an old coil -- tune-up suggestions
Probably the most useful thing to do, and very educational for all involved,
would be to first "characterize" the coil using Tesla coil design software
that will analyze the physical parameters of the coil, determine resonant
frequencies of the primary and secondary circuits, help you determine the
optimum value for the tank capacitor, and provide an initial tap point for
the primary coil.
If you use one of the TC design programs to analyze the coil first, you will
get a good understanding of how the various parts interact with each other.
This way, before you ever power up the coil, you can be sure that the
resonant frequencies of primary and secondary circuits are close enough to
be brought into tune by selecting the appropriate tap point on the primary.
If the coil can't be brought into tune, you'll get poor (or zero) output.
Some of the useful applications are:
Wintesla, by R. Scott Coppersmith
(http://www.hot-streamer.com/rscopper/index.htm) (see version 188.8.131.52)
JAVATC, by Bart Anderson (http://www.classictesla.com/java/javatc.html)
ScanTesla, By Terry Fritz (not sure where this is archived right now, but
there's a bunch of useful design and analysis software available at
http://www.hot-streamer.com/TeslaCoils/Programs/Programs.htm. The user guide
for ScanTesla is at
All of these applications can be downloaded at no cost.
Good luck ....
----- Original Message -----
From: "Jason Goodman" <goodman_jason at wheatonma.edu>
To: <tesla at pupman.com>
Sent: Tuesday, November 13, 2007 12:40 AM
Subject: [TCML] Fixing up an old coil -- tune-up suggestions
> Hi, all, I'm new to this list. I'm a physics professor at a small
> liberal arts college. About 5 years ago, before I was hired, one of our
> physics students built a tesla coil for his senior project. It's been
> gathering dust in our machine shop ever since. Some of my current
> Electricity and Magnetism students and I are working on putting it back
> into working order.
> We haven't been able to find the original construction plans which the
> student followed to build it; if you recognize the design, a link to the
> plans would be appreciated.
> I've got several questions about getting this thing tuned up and working
> well, so let me describe it first. Here are the vital statistics of the
> coil as we found it. I'm writing this from home, so I'm going by memory
> 125 v->12.5 kv transformer to power primary circuit, toaster-sized white
> box (neon sign transformer?)
> 6 brine-filled glass bottle capacitors made from root beer bottles
> Spark gap: single gap made from two trailer hitch balls mounted on a
> wooden frame
> Primary circuit wiring: Heavy gauge wire (4-gauge? 6?) with pretty thick
> insulation, type unknown. Alligator-clip connectors to primary coil.
> Primary coil: Inverted conical helix made from 1/4" copper pipe, about
> 7-8 turns, smallest diameter 14 inches, largest diameter 30 inches,
> height about 20 inches, mounted on triangular plywood supports.
> Secondary coil: 14-16 gauge wire on white PVC pipe, 5"ish diameter, 36"
> Top load: 30" toroid made from 4" diameter metal ventilation ducting,
> mounted on foil-covered plywood disk.
> There are no safety or protection circuits built into the system as we
> found it -- no safety spark gap across the transformer, no filters or
> switches on the mains side of things, no grounding rail above the
> primary, all stuff I've read about. I've made it very clear to the
> students that the primary circuit is absolutely lethal... I'm not sure
> they took me seriously at first, but they sure did once they saw and
> heard the spark gap firing.
> The bottle caps had been sitting filled for five years. Exciting
> chemistry had taken place between the brine, the oil, and the metal bolts
> used as electrodes, leaving an unholy sludgy mess inside. We just threw
> these out, replacing them with a six-pack of Corona (heh) bottles, built
> more or less according to http://www.pupman.com/
> We wired the thing with the supply transformer bridging across the
> capacitor (http://en.wikipedia.org/wiki/Image:Tesla_coil_4.svg ) -- I
> now understand that it's better for the transformer to put the
> transformer bridging across the spark gap (http://en.wikipedia.org/
> wiki/Image:Tesla_coil_3.svg). The "ground" end of the secondary was
> attached to a copper pipe providing compressed air throughout the
> We placed a grounded pipe (galvanized 1/2" steel electrical conduit) near
> the toroid to draw a spark.
> We first ran a test of the power supply without the primary coil in the
> circuit, shorting the alligator clips together. With the spark gap too
> wide, we heard a hum and a quiet snappy crackle. We could see some
> corona discharge from the aluminum foil surrounding the bottles, but they
> didn't seem to be heating up etc. With the spark gap set at 5-7 mm, we
> got a nice loud, bright spark, and the students were impressed.
> When we hooked up the primary coil, a fluorescent tube held in the hand
> lit up from about 6 feet away. We got corona discharge from the end of
> the grounded pipe to the toroid when the end was about 8-10 inches away,
> and occasional dim sparks when the end came within 6-8 inches. When the
> pipe end was raised so the shaft of the pipe rather than the end was
> closest to the toroid, we could draw a steady crackle of bright sparks
> 5-6" long.
> Tuning was done by adjusting the position of alligator clips on the
> primary using trial-and-error, just fiddling to try to get the longest
> spark. Best we could do was 6-8 inches of spark.
> So, not too bad, but I feel like this coil is probably capable of more.
> Questions for you:
> 1) What should we expect from this coil?
> 2) If we should expect more, is the problem likely one of LC tuning, or
> should we be looking for power loss elsewhere?
> 3) Is it worth going to the extra effort of measuring the resonance of
> secondary and primary using an oscillator and oscilloscope and tuning
> that way, or is that just lipstick on a pig at this point?
> 4) Is a little corona discharge from the bottle capacitors a problem?
> If so, how can we correct it? (Trim sharp edges from the aluminum foil?)
> 5) Do the two circuits mentioned earlier perform equally well, with the
> only difference being protection for the transformer, or does one give a
> better zap?
> Thanks for any help you can give. Please keep in mind that we're not
> interested in redesigning and rebuilding this from the ground up: we just
> want to get it working to original design spec.
> Tesla mailing list
> Tesla at www.pupman.com
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