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Re: Thin vs. thick wire with fewer turns, observations.

In a message dated 99-11-15 05:55:07 EST, you write:

<< Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
 
> Hi John,
 
>   From the information you give and making a few guesses, I would estimate
> that the output impedance of your coil went from 327K ohms down to 111K
> ohms with the changes you made.  

Hi Terry,

Thanks for reminding me about the impedance issue, I hadn't been
thinking about that!  This might explain the results I've seen in some
other TC tests too.  It is possible that my coil was well optimized using
the original wire, for that physical size of coil.  By going to a
thinner wire, such as #30, with even more turns, the Z match should be
a little better, but then wire losses might start to have an effect and
begin to negate any matching advantage.  I was never one to think
that thick wire was that important, but I guess there's some limit to
how thin the wire can be before it has a noticeable negative effect.
Still, it would be interesting to wind a coil that gives a perfect match
based on your optimal match theory to see if it improves the 
performance even more.  By making the coil physically larger and
wider, it should be possible to obtain an optimal match without using
very thin wire.
 
> If one assumes that a streamer presents a load of 220k in series with 5pF
> (Z=416K at 90kHz and Z=263K at 200kHz) then your old set up was probably
> impedance matched better to the streamer load than your new setup.  
 
> Assuming a bunch of stuff, your streamers would have been receiving 225
> watts before and 140 watts now.  Assuming streamer length is proportional
> to the square root of output power (and input power too assuming more
> stuff), I would expect your new system to give streamers 80% of the length
> of the old setup.

My sparks seem to be 7% shorter with the #20 wire than with the #28.
( I measured the spark lengths more carefully, and I would say they are
39" vs. 42" before.)
Maybe there's some variability in the loading and matching that lets
the TC tolerate a poor match better than expected.  A poor match would
help to explain why my gaps seem brighter too....the energy can't get out
of the system, so it reflects back to the primary and burns up in the gaps
instead.  My quenching should be poorer now by that theory, but I haven't
checked it on the scope yet with this new setup, but the extra gap 
brightness does suggest this.

In re-thinking the gap loss issue, it seems my surge impedance vs.
Rgap should be about the same as before, so that shouldn't really be
a cause of what I'm seeing.  That would leave only frequency and
matching as possible causes of my spark length decrease.  Gap
losses would of course be higher if matching is the problem, but
not because of primary Zsurge as I mentioned above. 

> Admittedly, the techniques used to determine all this are a bit new and
> barely tested.  However, in your case, the results seem to follow the
> predictions.  With better streamer load data, such impedance matching may
> really help in determining what the best size and type of secondary to make
> to produce the best sparks.  I still find it hard to believe that 220K ohms
> in series with 5pF is the impedance of ALL secondary arcs.  However, it
> always seems to work in every case so far...

It's all very interesting.  I'll apply these ideas to some of my other coils
too, and see what I come up with.  This might explain why many small
TC's are rather inefficient; they will tend to have poor matching unless
they are wound with thin wire.  
 
> Thanks for providing this valuable information!  It has great meaning to 
me...

Thanks for bringing up the matching issue again.  I think it may hold
great promise for TC design!

I did a few other tests too.  I tried various toroid sizes but nothing helped.
I also tried 240 bps, but the "efficiency" was bad as usual at this higher
break rate.  I needed 55% more input power at 240 bps to obtain the
same spark length as at 120 bps.  This needed power increase was
even worse than in my previous 120 bps vs. 240 bps comparisons.

I also noticed that corregated toroids seem to produce about 10 times
more ozone than smooth ones in this system.  All the little ridges must
be sprouting corona to some degree, and this is probably enhanced by
the weak output.

Regarding racing sparks, when I removed the old wire from my coil, I
saw quite a few burned spots on the form from racing sparks.  These
spots were all on one side of the form which faced the needle that I
use for tapping the primary which indicates that the voltage and
corona stresses were triggering the racing sparks facing the needle.
I eventually learned to cover the needle with poly to prevent this.  
Interesting also, was that the burned spots were separated by 
exactly the same spacing vertically in many cases.  Most often, this
spacing was about 1.25" or so.  This even spacing hints at higher
order resonances as a cause of racing sparks.  It would seem both
that voltage stresses, *and* these higher order resonances were
working together in this case to cause racing sparks.

Cheers,
John Freau
 
 >Cheers,
 
 >  Terry