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Re: [TCML] Tesla's topload



Phil,Dave, All,

My gut feeling is that the effect is quite small, especially with smooth top loads (spheres/toroids). Because of this, any breakout loading will overwhelm the additional field created capacitance.

As it happens, the coil that I am building at the moment is a classic SSTC with a non-smooth toroid design. As it utilises base current feedback, I'm hoping that running the coil with no visible breakout, I will see a resonant frequency change as the bus voltage is increased, indicating a change in the capacitance of the top-load. This should prove or disprove the theory.

Also as Tesla coils are an AC system, it would also suggest that the capacitance of the top load would vary over the period of the driving frequency, with zero crossing having minimum capacitance and peak voltage points having more. This should be seen in the shape of the field waveform measured in open air near the coil. A comparison to a similar sized but more conventional topload would help to eliminate any driver/coil related waveform shape irregularities.

Cheers
        Derek



On 06/04/2011 23:14, Phil Tuck wrote:
Derek, et al
If it did then people would have noticed an anomaly in the tuning figures by
now I think. We know that best performance generally occurs when the primary
is set to resonant lower than the secondary because of the streamer loading
and this normally is by an amount of around 1.5pF per foot. However, if what
you say were right, then would we not have noticed additional factors at
play on the bigger coils that could not be accounted for purely by streamer
loading alone?

Regards
Phil Tuck

www.hvtesla.com



-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of Derek, Extreme Electronics
Sent: 06 April 2011 05:49
To: Tesla Coil Mailing List
Subject: Re: [TCML] Tesla's topload

This does raise an interesting question, does the capacitance of the topload
increase as the voltage on the topload increases because the field around
the topload adds to the effective external dimensions of the topload, so
increasing capacitance ?

      Derek


On 06/04/2011 01:48, bartb wrote:
I dunno, it would be interesting to model: say of sphere's with
diameters equal to a corresponding toroid minor diameter, but with the
spheres spaced apart so that 1/2 of the diameter of each sphere
intersects the other creating large bumps of sorts. Unfortunately not
something Javatc can do as the topload sphere's would have to be
offset from center (not something it can do now). Possibly Paul or
Antonio's software could do a quick and dirty comparison.

Take care,
Bart

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