Re: [TCML] Tesla's topload

["Derek, Extreme Electronics" <tesla@xxxxxxxxxxxxxxxxxxxxxxxx>]

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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