Re: OLTC update - Poor seconadry Q

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <FutureT-at-aol-dot-com>

Jimmy,

The predicted length can be beaten, esp at higher powers.  The
more complex formula takes this into account, and gives a 
somewhat longer spark length prediction for larger coils.  This
new formula also takes break rate into account.  I used various
math roots to create the needed "skewing" of the results.  I used
whole number roots rather than non-whole number roots for simplicity,
although non-whole number roots would give better accuracy.  Actually
someone eventually mailed me a formula they made along the 
same lines as mine, where they used non-whole number roots and it 
gave better results.  I must admit that I just don't have enough
data to know what breakrate results are due to variations in
coil design by various builders, and what part of the results
stems from actual spark growth characteristics due to breakrate
differences.

The more complex formula follows, but I must admit I don't
trust it all that much, and as I mentioned, it would benefit from
the use of non-whole number roots.  

Spark length inches =
    [(3.9*16th.root watts)*sqrt watts] / 4th.root BPS

(for 120 - 480 bps)
(watts are wallplug watts)

I would estimate that the lengths predicted by my formula are
far above the average spark length, especially for smaller coils.
For example, many 12/30 NST powered coils give only about
an 18" spark or so, which falls far short of the 42" that my
formula predicts, and which my old research coil achieved.
Many small coils are limited by; poor spark gaps, too small
toroids, too few primary and secondary turns, etc.  It would
be really tough to beat the 42" spark length for a 12/30 NST
(600 watts), by any significant amount I think.  Actually, I've 
never heard of anyone beating that result.

At higher powers, many well designed coils meet or slightly 
exceed the formula's predicted spark lengths.

John


>
> that was another question i was going to ask. when you say efficient coils do
> you mean it is really tough to beat the predicted lengt? or just a little
> above
> average? out of 100 randomly selected coils, how many would meet or beat the
> prediced length? also what is that more complicated formula that you didnt
> post
> on your page? 
>
> Tesla list 
> >
> > wrote:  
> > Original poster: "by way of Terry Fritz " 
> >
> > Jimmy,
> >
> > My equation is reasonably accurate at around 300 watts. 
> > Here's some sample tests from 6/8/99.
> >
> > watts toroid predicted length actual spark length 
> > 280 3" x 10" 29" 27" 
> > 280 4" x 13" 29" 27"
> >
> > I didn't need to test a lot of different coils because my 
> > equation is not for the average coil, but only for efficient 
> > coils.
> >
> > John