Hi Jan,
> 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.
I am increasingly suspicious this is my problem. I am building a winding
jig based on a design I found, and have bought more form and magnet wire.
If the second coil doesn't work, it's either not the problem - or I'm so
terrible at this I should take up a different hobby!
> One good way of checking the resonance was suggested by Antonio M.
Querios, to feed a low frequency square wave,
A frequency generator seems to be in order for my Christmas wish-list...
Thanks,
Joshua Thomas
On Wed, Nov 3, 2021 at 6:35 AM Jan Ohlsson <jan@xxxxxxxx> wrote:
> 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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--
Joshua Thomas
My new email address is: joshuafthomas@xxxxxxxxx
Please update your information if you have not already done so.