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RE: [TCML] Racing arcs and primary resonances
Instead of all this rhetoric about scoping the primary, Doodle's Theorem,
blah, blah, blah, why don't you just try tuning your coil? Might I suggest
the following:
Add some stationary gaps in series with your RSG
Add some ballast resistance in series with your pot
Adjust the primary / secondary coupling to optimize / eliminate racing
sparks
Adjust the timing on your sync motor
Is the corona ring big enough to prevent flashover?
Adequate insulation on the secondary?
Might take some time, but eventually you should be able to do all this by
ear
Example: Zotzilla
http://www.youtube.com/watch?v=6WsT9hHGdfY
<http://www.youtube.com/watch?v=6WsT9hHGdfY&feature=related>
&feature=related
Specifications:
8 rotating studs at 1800 rpm with 4 gaps per bang in series with 5 static
gaps; that's 9 gaps per bang. FYI: power arcing develops without the
stationary gaps
Burden resistor of 0.1 to 0.2 ohms for ten foot arcs at 240 volts / 45A /
7.5kw / 12kv input to primary. FYI: power arcing develops without the
ballast resistance
Careful adjustment of RSG timing. FYI: serious RSG flame-over develops when
timing is not properly adjusted
Careful adjustment of primary / secondary coupling; optimized for maximum
spark length without racing sparks
Once you've done the above steps, your coil should run like a Swiss watch
Additional info on this old coil can be seen at:
http://audiotesla.org/zotzilla.htm
Good luck,
Hank
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of DC Cox
Sent: Sunday, April 03, 2011 11:03 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Racing arcs and primary resonances
You may be able to replicate this performance by purposefully building a
poor design gap (small electrodes, etc) and then overpowering it at 8-15
kVA.
Dr. Resonance
On Sun, Apr 3, 2011 at 12:43 AM, Paul Nicholson <tcml88@xxxxxxxxxxx> wrote:
> John wrote:
> > There were no racing sparks at full power until the gap
> > heated up for 10 seconds or so, then the racing sparks became
> > progressively worse within a few seconds until the secondary
> > was covered with a mass of racing sparks. If I then let the
> > gap cool down, and went to full power again, the process
> > repeated.
>
> Gary Lau wrote:
> > I would think that if a static gap overheats, its breakdown
> > voltage would be reduced,
>
> These comments are compatible with each other, and with
> Brandon's racing arc condition.
>
> In both cases described, the supply transformer secondary
> voltage is trying to rise above the level at which the gap
> fires, either because Brandon has turned up the variac from 80V
> (firing point) to 140V (racing arcs start), or because John's
> spark gap has heated and closed up a little.
>
> The description of secondary racing arcs in both examples is
> the same and indicates HF activity in the secondary.
>
> I wrote:
> > When the variac is turned up beyond the level required for
> > normal firing, without opening out the spark gap, is this
> > likely to excite extra HF oscillation, perhaps through
> > negative resistance arc behaviour interacting with the
> > spectrum of primary resonances.
>
> I propose from the comments so far the hypothesis that the
> oversupply to the gap is pushing the arc into some sort of
> Poulsen resonance with one or more of the primary overtones.
>
> Some notes on Duddell 'singing arcs' and Poulsen arc
> generator can be found here,
>
> http://www.qsl.net/vk5br/Before_Valve_Amp.pdf
>
> and the whole document is quite a nice read.
>
> The thing to note is that the effect arises with a series-tuned
> circuit across the gap, which would be provided in this case
> by the half-wave (and multiples) modes of the bare primary
> coil. The primary cap is in series with this series resonator
> and has little or no effect.
>
> Some ways to test/refute this:-
>
> - The effect should not be seen with solid state gaps;
> - The HF should be visible in the scope and frequency should
> agree with calculated or measured half-wave primary mode;
> - It should be possible to reproduce the effect on any static
> gap coil where the supply is enough to overdrive the gap;
> - The HF should be tunable by bringing up an earthed plate
> near to the primary coil.
>
> Examination of primary current waveforms is required, looking
> for HF components which increase significantly as the variac
> is turned up beyond the normal firing point.
>
> Brandon has a 'scope available, and can presumably rustle up a
> CT for the primary current. I can torture some modelling
> software to make it calculate roughly the primary overtones.
>
> --
> Paul Nicholson
> --
> _______________________________________________
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> Tesla@xxxxxxxxxx
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>
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