Re: Tesla Coil Blunderbusses

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Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Malcolm,

At 01:38 PM 4/18/2001 +1200, you wrote:
>Hi Terry,
>
><snip>
>> I designed my small coil taking the streamer loss as 1pF/ft in series
>> with 220K ohms.  I also designed it so that with this load it would
>> automatically run out of energy on the first notch and "self quench". 
>> As it turns out, it all really did work just perfectly!  That
>> 1pF/ft+220K thing has never let me down.  I am sort of surprised such
>> a simple estimate for streamer load seems to be holding up so well. 
>> In this case, getting a good estimate of the streamer load was very
>> improtant since it had a very big effect on the time it would take for
>> the secondary to ring down.  I am still not sure it was worth all the
>> time and effort to get it to do that, but the design models ended up
>> predicting the real coil's behaviour very well.
>
>Was that streamer load air terminating or attached (to something)? 

In air with NO ground strike.

>Pondering further I realize that for air streamers where energy 
>trades continue, tuning to the streamers would definitely improve 
>performance. For a single pri-sec trade, I can't see that it should 
>matter. Which still leaves the question of what I clearly observed 
>when tuning the primary to the LSB. I don't have the modelling tools 
>handy. Would you mind trying it in uSim and posting the results? Any 
>info that links pri-sec tuning to gap firing conundrums would also be 
>welcomed.

When the secondary hits ground, the energy is suddenly all lost from the
system and the cycle is over.  Specifically trying to push all the energy
into a single "jolt" to try and hit ground may indeed have a different
design "load" other than 1pF/ft+220k.  However, I can't imagine that
differing much from my first notch auto quench coil...

>       How exactly did you go about designing a coil for that 
>particular streamer load? 

Massive trial and error.  With each "test" parameter, the gap timing,
output impedance, primary cap size, etc. would shift and I had to
re-optimize everything.  At this level, John Couture's program is not
available to do it all for me :-) 

>I note in passing that 220k cannot be the 
>ultimately definitive figure for equaivalent arc resistance but must 
>be true only in limited circumstances. I hark back to what I said 
>about welder arcs.

That is for a streamer to air load.  It works for my small coil and Greg
Leyh's Electrum as a "design number".  There are some discussions as to why
that remains constant but it never has been independently arrived at.  It
works great for my simulations but I suspect it will be improved upon much
as time and knowledge goes on.  Right now, it is all there is to design by.
 It has always worked great for me.

Cheers,

	Terry

>
>Regards,
>malcolm
>