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Re: Primaries



Malcolm,

Good luck on the new coil! A 45 pF topload on top of a 16" diameter coil
should make for a pretty good sized coil for a 2.3 kW system! Re: gap
losses - it seems like nature and physics has conspired to limit primary
Q. The negative resistance characteristic of the gap arc is a fortunate
phenomenon(!) - think of the losses if it had a positive characteristic!
Unfortunately, it seems that whatever current primary current levels we
run, the arc compensates (and limits us) to a primary Q of 10-12. 

One way to improve the system efficiency would be to maximize the
coupling coefficient so that more energy transfers to the secondary
quicker, reduccing the duration of the gap losses. If we can succeed in
quenching the gap immediately after the first energy transfer, we've
should maximize power transfer. With a 2-coil system, this is probably
"practically" max'ed at k=0.22. If you're able to hit higher "magic" k's
without breaking down the secondary or flashing to the primary, AND if
you can quench the gap, you should be able to break 2-coil records.
Otherwise it looks like a maggie is the only way.

Good Luck!! 


-- Bert --

Tesla List wrote:
> 
> >From MALCOLM-at-directorate.wnp.ac.nzSun Sep 22 22:33:43 1996
> Date: Mon, 23 Sep 1996 09:28:17 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Primaries
> 
> Hi all,
>        I have some questions I would appreciate some answers to.
> (1) To Greg Leyh : You mentioned some figures for gap current and
>     gap conduction voltage the other day. How did you measure those?
> (2) To Richard Hull : Have you tried primaries with v. large L/C
>     ratios (for example, L of 200uH+). If so, how well did they work?
>     Was there any improvement over say 100uH? I am assuming that
>     the bang size and break rate was kept constant.
> (3) Also to Richard : Have you _ever_ measured a dynamic primary Q
>     above 10?
> 
>     I have desgined and am construction a low frequency secondary for
> a number of different experiments, several different types of systems
> and also to have a crack at setting a record for around 2.3kW. I am
> constantly running into a barrier with the primary and in particular
> the gap losses. It seems that this is almost the sole determining
> factor of system performance and I am desperately trying to find a
> way to improve it without resorting to exotic devices. For your
> interest, resonator spec is:
>     L about 140mH
>     Cself around 24pF
>     Winding Height 39"
>     Diameter 16.5"
>     Closewound with 0.9mm diameter wire
>     Former = open frame (simply because I don't have any pipe).
>     Predicted Fself around 87kHz
>     Predicted F with around 45pF topload about 50kHz with a range
> of frequencies in between for smaller toploads.
> 
>     I am currently constructing the former which is turning out to be
> a tricky exercise with the materials I have on hand.
>     An analysis based on a dynamic primary Q of 10 suggests that the
> lower in frequency I go, the smaller the gap losses become.
>     If anyone has any input on this or comment to make I would
> welcome it. I am just about at the end of the rope with regard to the
> primary. I had hoped late last week that gap losses might reduce with
> a drop in gap current but it seems that hope is doomed.
> 
> Malcolm