Re: Primary inductance vs. coupling

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

Original poster: "Jason Petrou by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jasonp-at-btinternet-dot-com>

Antonio, John, all,

> The coupling coefficient depends essentially on the geometry of the
> coils.
> More or less turns make little difference.
> If the coupling coefficient and the resonance frequency of the primary
> and secondary are kept constant, larger or smaller inductance
> at the primary result in the same voltage and current waveforms
> everywhere,
> just scaled in amplitude.
> There is nothing that can be identified as "overcoupling" in a Tesla
> transformer. Excessive coupling can cause sparking between the two
> coils, and maybe irregular voltage distributions along the secondary
> that
> can cause sparks in the secondary windings, but this has little direct
> relation with the coupling.
Sorry, by overcoupling I meant a coupling that was too tight, too close to
1.

> > Also in case anyone's interested I am consistently finding that with
higher
> > breakrates I can increase the coupling... has anyone else noticed this?
> > John, I believe you said something about this at one point...
>
> Higher coupling reduces the energy transfer time, up to a minimum with
> k=0.6, and asks for higher break rates. Maybe you have hit a point of
> optimal energy transfer.
This is the reason that I thought that a larger primary inductance would
allow an increase in coupling. As you increase the coupling the energy is
transferred more quickly, therefore if you make a larger primary which
stretches the resonant rise over a longer period then this moght combat the
problem, allowing a faster energy transfer and maybee less loss in the gap.
I have a feeling that this would apply to only static gaps as they self
fire.

John, RE the bang size, I have found that this is definitely the case when I
use a way LTR cap (35nF). I guess that because the cap is so large for my
xfmr (10/80 neon, res. 18nF cap) it can only charge to a certain point
before it discharges, thus allowing you to have a faster energy transfer to
the secondary.

By the way, I noticed that when running very LTR (35nF) as opposed to 1.5x
resonant (25nF) the current draw on the mains is larger by about 500mA,
which is to be expected. This change does not happen when PFC is added to
the low voltage side of the neon... I wonder if the primary cap on the high
side is acting as a PFC cap too? This would indicate that the cap is not
fully discharged (by any means) after the gap has fired. The breakrate also
seems to have an effect on this - 200 breaks lowers the effect. Any clues to
what is happening?

Best R,
Jason