Re: Another capacitive transformer TC

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

Original poster: "Jolyon Vater Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

Antonio,
Measuring C3 without sophisticated equipment would appear to be
problematic -would it be best to design as a directly-coupled
transformerless TC and then reconfigure it as a capacitive transfomer (as I
have done);
I have a meter capable of reading capacitance
down to 1pF -would this be of any use?

I have experimented with changing the elevation of the ring with respect to
the coil L2
Lowering ring had little obvious effect on spark length or corona production
at the terminal
-although this may have been obscured by low power of the HV supply
(rectified
ignition coil).
Raising the height of the induction ring resulted in mild corona appearing
in the middle
of the ring where the metal foil abuts the plastic "spark-guard", which
developed into
actual arcing from L2 into the encircling space when the topload was
removed.
Apparently, no functional damage to L2 or puncture of of the spark-guard
occured and
normal operation resumed when the topload was replaced.

This suggests that spacing between the ring and L2 should be increased in
proportion to the elevation of the ring to prevent corona or arcing-
but doesn't the bigger separation increase the parasitic capacitance C3 by
allowing more field lines to escape capture by the ring
-or does perhaps the higher voltage that can be premitted between L2 and the
ring without arcing allow the same amount of energy  (or more)to be stored
in C2 despite the fact that its capacitance is smaller?

Wouldn't an inverted-cone -shaped induction ring be more effective in
maximising C2 and minimising C3 than a flat ring?

Also does it not suggest that the terminal size be increased proportionately
to the elevation of the ring -again to prevent arcing or corona?

Incidentally, I have seen a similar effect with regard to the primary tap on
my  inductively-coupled
TC, where reducing the number of turns to the tapping point causes
ultimately  causes
primary-to-secondary insulation to breakdown with the appearence of
  "racing" sparks
(?) ; the problem disappears when the terminal size is increased.

Jolyon
Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, September 22, 2002 5:27 AM
Subject: Re: Another capacitive transformer TC


> 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
>
>
>
>
>