Hello Alex,
Thank you for your reply.
I have an oscilloscope but not a signal generator (the pitfalls of being on
a tight budget!). If I can source a signal generator I will try your
technique to find resonant frequency; thank you for that.
I am somewhat surprised to read that the primary coil needs to be tuned
with with-in 1/4". The other sources I have been reading who have had
successful coils started out with a "guessed" turn to tap the primary coil
and then advanced or retarded the tap point by an entire turn of the coil,
which is far more than a 1/4". Others seemed to have generated sparks even
with a sub-optimal tap point, using the tuning to get optimal length.
Perhaps you could elaborate more on this?
Thank you very much,
Joshua Thomas
On Mon, Nov 1, 2021 at 2:52 PM b alex pettit jr <a_pettit_jr@xxxxxxxxx>
wrote:
> Josh,
> Do you have an oscilloscope and signal generator capable of 250 KHz ?
> *The Primary Coil must be tuned to within 1/4" for proper operation.*
>
> *1) Find the resonant freq of the Secondary :*
> Connect the signal generator through a 50 ohm resistor through the Primary
> Coil ( no capacitance )
> Set a scope input coax with a few inches of wire a few feet from the
> Secondary.
> Sweep the signal generator through 100 KHz - 300 KHz and see if can
> determine the resonant frequency of the Secondary.
> ( bring probe closer as required )
>
> *2) Tune the Primary Winding & Cap to the Secondary Freq.*
> Hook the Primary Coil and Capacitor in in parallel and in series with the
> 50 ohm resistor.
> Connect the scope across the resistor and drive the system with the signal
> generator ..
> Keep adjusting the coil tap until the primary ( Pk oscilloscope signal )
> matches the Secondary.
>
> |-------*L*-------|
> ----------*R* ------| |-----------------
> |--------*C-*-----|
> * ^-- Scope--^*
>
> * ^ ----------Signal Generator --------------^*
>
> There will be some mis-tuning when you apply actual HV power, but you
> should be within 1" on the primary of being
> at the proper tap point.
>
> Alex
>
> On Sunday, October 31, 2021, 11:31:45 PM EDT, Joshua Thomas <
> joshuafthomas@xxxxxxxxx> 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
>
>
>
>
> --
> 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.