Re: Another capacitive transformer TC

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
> 
> I have tried the mini-coil in capacitive transformer mode and it works:
> corona/streamers are  clearly visible around the terminal -especially in
> subdued light- and 1/2" sparks can be drawn from.

Good. With the same elements of the directly coupled system the 
capacitive transformer coil transfers energy in about twice more
time, and so the losses are higher.
 
> For and induction ring I used an 8" diameter disc with 2" centre hole on
> plastic insulators 2 5/16" high; the hole is fitted with a spark-guard a wrap
> of stiff 20 mil plastic sheet prevent the mild arcing to L2 experienced in
> first experiment
> L2 also given second coat of epoxy varnish to diminish the likelyhood of a
> recurrence;
> and since the spark-guard was added, so far there have been no problems.

The ring can be at some distance from the coil, and can be just a wire
ring.

> I have noticed that when the ring is grounded corona activity at the terminal
> increases- is this because the influence plane has been enlarged or
simply that
> the effect of grounding the ring is simply to turn the TC from a capacitive
> transformer into a directly-coupled transformerless TC with better
efficiency?

If you changed the position of the ground connection of the primary 
circuit from the normal place (bottom of L1) to the ring, and kept the
bottom of the resonator L2 grounded, you obtained a version of the
directly coupled coil. If you just added a ground connection grounding
the ring, something is strange.
 
> For greater output, I have tried changing C1 from a 255pF saltwater gel
cap to
> a much larger 3nf capacitor (a 2 litre pop-bottle SWC)for greater output -so
> far without success as there was then much less output at the terminal
-despite
> the greater energy stored in C1.

The problem with this is that the two distributed capacitances (from the
terminal/L2 to ground (C3) and to the ring (C2)) would have to be scaled 
in the same proportion. You had originally 2.8 pF for both. 
With 12 times more primary capacitance you need 34 pF for the two 
capacitances. This requires quite large dimensions for the terminal and 
ring. Instead of this, you can reduce L1 to compensate, keeping the 
relation L1*(C1+C2)=L2*(C2+C3).
 
> Is the observed poor performance with larger values of  C1 likely to be
due to
> poor coupling (as calculation suggests value of C2 should be proportionally
> increased) or is there another effect so far not examined -only I have tried
> increasing the terminal capacitance with small toroids with little or no
> observed effect. Might the induction ring also have to be enlarged?

If C1 is increased, the system must be retuned, or by increasing C2+C3,
or by decreasing L1. Decreasing L1 slows down the energy transfer, and
increases losses, but increases the voltage gain (sqrt(L2/L1)), and
it's always better to have the system correctly tuned. The larger 
initial energy by far compensates the losses.

Antonio Carlos M. de Queiroz