Hi Joshua,
That is a nice setup, It should work.
The NST and spark gap are proven ok by your tests, so no problems there. Your MMC is also of proven design, with good caps. Either the primary circuit is grossly out of tune with the secondary, or there is a shorted turn in the secondary coil, removing the energy.
The JavaTC simulator is surprisingly accurate, if the input values are correctly given. It should give you the number of primary turns for resonance within a quarter turn or so.
One good way of checking the resonance was suggested by Antonio M. Querios, to feed a low frequency square wave, for example 60 Hz, to the primary circuit through a series resistor, and put the scope across this resistor, with the spark gap shorted. This is a measurement of the primary current waveform. At resonance you will get the typical damped oscillations on the underlying square wave, with max ringing amplitude when primary and secondary resonance frequency are equal. A shorted turn in the secondary would of of course prevent the ringing.
The resonance frequency will change somewhat when the coil is run in the normal way, because of ionized air around the top load, but not much.
Regards,
Jan
Skickat från min iPad
> 1 nov. 2021 kl. 04:31 skrev Joshua Thomas <joshuafthomas@xxxxxxxxx>:
>
> 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
>
>
>
>
> --
> Joshua Thomas
>
> My new email address is: joshuafthomas@xxxxxxxxx
> Please update your information if you have not already done so.
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