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Re: Real data from real experiments.



Tesla List wrote:
> 
> >From MALCOLM-at-directorate.wnp.ac.nzMon Nov 18 20:08:35 1996
> Date: Tue, 19 Nov 1996 08:40:54 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: Real data from real experiments.
> 
> Hi Chuck,
>            This might not seem terribly helpful but in choosing a cap
> you are looking at a balance between bang energy and gap losses. For
> example, if your transformer can charge a _1 uF_ cap to the full peak
> voltage the transformer can supply, you have 10x the bang energy of a
> 0.1uF cap which can only get charged to the same voltage, BUT the gap
> losses are going to be 10x that figure as well (for a given k) since
> the primary inductance has to be dropped 10x to maintain tune
> (remember gap loss scales with I to a first approximation). You run
> into the law of diminishing returns. It would be desirable for
> example, if you are running 200BPS with a 1uF cap and that is the
> maximum size your transformer can fully charge at that break rate, to
> halve the cap size and double the break rate because, although gap
> losses are roughly the same, the extra repetition will maintain
> stronger spark ionization. At some point (I've heard around 600BPS)
> there is no further gain in upping break rate. In summary, a good
> rule of thumb then is to choose the maximum capacitance that can be
> fully charged at around 500 - 600 BPS or less if your break rate
> doesn't go that high. A sense of balance also helps. To get the best
> use from a large cap you need to run at a low frequency - the lower
> the better so you can maximize primary surge impedance.
>      If you plan on running at half the break rate and your supply can
> fully charge twice the capacitance at that break rate, double the
> capacitance. Using the highest k your system can stand also reduces
> gap losses since the gap has to conduct for a shorter time to effect
> energy transfer.
>      I'm sorry - I don't have specific figures for pigs as I don't
> use them at this stage. Perhaps Richard Quick, Hull or some one else
> who is experienced in pig coiling can help with the max sized cap you
> can stand. Also, the choke used with the pig can also assist in
> boosting cap charge beyond or below raw pig capability depending on
> its inductance - for a given break rate and capacitor, a small
> inductor will boost charge and a large inductance will hinder it.
>      Greg Leyh wrote a great piece on this in his TCBA article which
> I don't have handy. All sounds a bit nebulous but I hope it helps.
> 
> Malcolm
> 
> >     The transformer is a 10 KVA pole pig at 14,400 VAC.  I use a
> > stationary/ rotary combination, up to 8 stationary gaps at .025" each
> > and the rotary is 12 rotating contacts on a 12" inch diameter, run
> > normally at 2500 RPM. Hope that helps.
> >
> > Chuck
> 
> PS - I designed my new resonator on the following basis :
> Min frequency 50kHz with a total secondary capacitance around 70pF
> and a height permitting peak voltages of a bit over a megavolt. To
> achieve 1MV with that capacitance I need to transfer 35 Joules per
> bang. With a topload of, say, 10pF (still permits a large radius of
> curvature because of mutual capacitance between topload and resonator)
> I need to transfer around 15J which is probably as much as I'll ever
> need with the supplies I'm planning to use. The extra capability is
> there though so this is the last resonator I need to build.


Malcom:
	Thanks alot for your comments.  I've gained several valuable points in
the last week or so which I hope will allow me to get as close as
possible to maximum spark.  Again, thanks!

Chuck