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Re: [TCML] Fixing up an old coil -- tune-up suggestions



Hi Tony,

I also didn't like the change. However, I've decided to give it a chance. Maybe I've been so use to one thing for so long that I am biased. So I'm going to let it go as is and give it it's due. Tonight, it all worked fine with my Thunderbird email client. Maybe it's just "me" who needs to get use to it.

Take care,
Bart


Anthony R. Mollner wrote:
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.
Tony

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx]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


Jason -

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 5.0.0.1)
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
http://drsstc.com/~terrell/modeling/ScanTeslaInstructions-700.pdf.)

All of these applications can be downloaded at no cost.

Good luck ....

Scott Hanson





----- Original Message -----
From: "Jason Goodman" <goodman_jason@xxxxxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
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
here....

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"
length
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.

Repairs:
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/
listarchives/1995/december/msg00040.html

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
building.

We placed a grounded pipe (galvanized 1/2" steel electrical conduit)  near
the toroid to draw a spark.

Testing:
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.
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