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Re: Sizing the toroid to the coil

Original Poster: FutureT-at-aol-dot-com


Hi John, 
I took a little time to reply as I've been thinking and computing about it. 
Comment below: 

>
> I think that Cself should be as small as possible compared with 
> Ctop within reasonable limits.  If we didn't have to worry about coil 
> breakdown, we could make our secondaries even smaller, and put 
> more power into the topload and into the arcs.  I see the Ctop/Cself 
> ratio as being simply a practical consideration of how small a coil 
> can be for a given power level.  (we must consider the losses too.) 
> I agree that the ratio is important, 
> but rather than saying that a certain ratio is ideal, i would just say 
> the the ratio should be as large as possible without causing 
> breakdown of the coil, and without causing too much loss.



Following your post, I took some time to take closer looks at Cself and why 2.8
worked. I came to the conclusion that CSelf (as used for Ctop design) is simply
a value that changes with the h/d ratio of the coil (at 2.8 - small changes in
Cself make considerable changes to Ctop). It is "VERY" similar to designing
Ctop by practical size measurements (e.g., if coil diameter is this size, then
Ctop should be that size). You are correct in every respect. Cself does not
correlate to what Ctop should or should not be. It has worked because the coils
of which the values were derived provided the practical ratio or ball park
value, but these coils were properly powered, therefore, Ctop was capable of a
breakout charge. 

This means my sparklength formula is flawed as well, but I think only in the
Cself & CTop correlation. It works only because the Ctop value is "practical"
as you stated. The rest of it simply calcs the energy available to the spark
channel. I'm looking deeper now and in different directions. Kind of got hung
up on the Q of the secondary and primary this week (beginning to think it's a
useless value in TC's). But that's another topic. 

Thanks for making me think about this a bit more, 
Bart