Is there a way to post photos of your setup?
A few things -
Do you know that the transformer is good? Draw arcs off each leg to
ground with a ground wire on a sissy stick, then try terminal to
terminal. A yellow glowing arc is what you want.
The capacitor voltage ratings are extrapolated from DC ratings and not
relevant to AC use. They are rated 300-500VAC at 60Hz, it will be far,
far less for RF use.
If I'm understanding the setup, you have 3 gaps in the spark gap between
4 copper pipes, plus fan cooling. This sounds excessive for 12kV and one
neon sign transformer. Maybe bypass one if not both gaps, or move the
fan further away. As for the resonant frequency, I'd ignore any goofy
simulators and just measure it. Get a frequency generator and
oscilloscope. Connect the frequency generator to just the entireÂ
primary coil and measure voltage on the secondary and sweep for maximum
rise. The resonant frequency will be somewhere near there. You'll thenÂ
have tune the primary to this. The dimensions indicate the secondary is
real heavy on capacitance. You may need to test with a smaller terminal
on the top. I don't hear much talk of this, but you can tune a tesla
coil by listening to the spark gap. A buzzing sound is what's ideal, not
a source of loud noise. It's similar to MIG welding. A smooth sound is
what you're after, not harsh noise.
On 10/31/2021 8:06 PM, Joshua Thomas wrote:
> Hello TCML!
>
> I'm having trouble with my first tesla coil. The specifications are as
> follows:
>
> * 12/30 Transco NST, GFCI removed
> * Primary coil: 0.25" copper tubing in flat spiral, 0.5" between turns,
> total 12 turns, 12" total radius from center. Height adjustable.
> * Secondary coil: 3.5" x 16" on PVC form, 28ga magnet wire, ~ 1100 turns
> * Topload: 4" dia flex PVC ducting torus, total diameter 18", 10" plywood
> center. Entire form covered with conductive copper tape.
> * Capacitor bank: 15x CDE 942C20P15K-F caps in series. 30kV rating, total
> 10 nF. 10M ohm 1/2W bleeder resistors across each.
> * Static spark gap of 4x 1" copper tube, microwave AC fan used for quenching
> * RF grounding rod of 1 ft, solid 1" copper, with 14 ga connection wire
> * Safety gap calibrated with variac to be just above normal firing voltage
> * Safety lowpass RC filter (aka ''Terry" filter) of 500 ohm, 100W wirewound
> resistor and 3x 15kV, 1nF ceramic caps (parallel); one RC set per HV line.
> F_cutoff ~ 106kHz
> * All HV connections made with 14ga GTO-15 wire.
>
> I've simulated this with JavaTC and it gives me a matching resonant
> frequencies around 230 kHz.
>
> First test was today. Spark gap works like a charm, banging away. Safety
> gap occasionally fires. Nothing at all on the secondary or topload. No
> corona, no arcs, CFL bulb put near the coil did not light up. A breakout
> point was attached, and a large metal object was put near it, and still
> nothing.
>
> Trouble shooting:
> * Removed the Terry filter. No change.
> * Changed tap point on primary coil from turn 8 to turn 7, no change.
> * Continuity checks on the secondary show normal, from topload to grounding
> strap.
>
> Thoughts:
> * My secondary coil is kind of terrible. First one I ever wound, and it has
> some wire overlaps.
> * A second check of my simulation suggests I should actually be using the
> entire primary coil instead of tapping at turn 8 of 12. Dunno why I did
> that. Would that have this much of an effect?
> * The RF grounding on this confuses me a little. I have a large metal strip
> attached to the bottom of the secondary. This has connections "in" from the
> safety gap and the terry filter, and "out" to the RF ground rod hammered
> into the earth. Is this how this is supposed to be wired?
>
> Thanks in advance for any advice etc. Glad a list like this exists, as no
> one in my department at the university (I'm a physics major) has any idea
> how TCs work.
>
> Joshua Thomas
>
>
>
>