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,

For the Ping circuit a 555 astable will be used
driven from 9 volt battery.
R1 will mainly control frequency and R2 will mainly control the "ping"
length.

I anticipate R1=100k
R2=1K
C1=10nF
that should give
Time high =0.7*(1e5+(2*1e3))*1e-8 = 707 uS
Time low = 0.7*1e3*1e-8 = 7 uS
Frequency 1400.560224 Hz.

Is this OK? I understand the "ping" is produced during the "low" period. Is
this due better current sinking than sourcing capability with a 555 or
faster switching time on the "low" than the "high" period?

Would variable frequency/ "ping" length be desirable?

Can Pin 3 be used for the direct excitation of circuits -without any
amplification or short-circuit protection for the IC or will this have to be
provided- any suggestions?Also, will a ground clip be necessary to act as a
return path for the signal?

I have a Telequipment D67 oscilloscope
(25 MHz dual-trace , analog not digital, with no storage capability) will
this suffice for observing the results of the ping test?
how are the test leads connected between the ping tester, the circuit to be
tested, and the oscilloscope?

Finally, could the "ping" tester also double as a lamp tester (with
antiparallel LEDs in Pin 3 output) to determine the resonant frequency
through the brightness of the LEDs?

Jolyon.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, September 28, 2002 8:54 PM
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>
> >
> > 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);
>
> When building my capacitive transformer coil I never had to measure
> this capacitance. I just tuned C2 and C3 simultaneously by looking at
> the voltage waveform over C1 while operating the circuit at low power
> (with a "ping" circuit made with a 555 timer in place of the spark gap).
> The element values listed in the web page were obtained by designing
> a network that fits the observed experimental waveforms (the mode)
> and the known elements C1, L1, and L2. The elements calculated for
> the directly coupled coil can be always used. The tuning relation
> for the directly coupled system is L1*C1=(L1+L2)*C2, and for the
> capacitive transformer version is L1*(C1+C2')=L2*(C2'+C3).
> With practical values, C2~=(C2'+C3), and any distribution of the
> terminal/L2 capacitance between C2' and C3 results in a working
> system (but with different numbers of cycles for energy transfer).
>
> > I have a meter capable of reading capacitance
> > down to 1pF -would this be of any use?
>
> It's difficult to measure C2 and C3, because they involve the self-
> capacitance of L2. In an approximate way, C2 and C3 can be measured
> with a capacitance meter between the influence ring, the terminal,
> and the ground, with the elements in their usual positions and
> insulated from everything. The capacitance of the meter leads must
> be discounted (discount the reading of the meter with the leads in
> the position where the measurement will be made, but disconnected).
> The self-capacitance of L2 would be then split in two and added to
> the measured values. The result will be a bit larger than what
> actually appears. You can also measure the self-capacitance of
> a coil, approximately: suspend it high above anything else,
> connected only to the meter, and measure its capacitance to ground.
> The self-capacitance is one half of what you measure.
>
> > 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?
>
> Ok, but if you increase C2 the voltage gain of the system decreases.
> No free lunch.
>
> > Wouldn't an inverted-cone -shaped induction ring be more effective in
> > maximising C2 and minimising C3 than a flat ring?
>
> Possibly yes. The ideal would be to eliminate C3, but keeping C2 as
> small as possible to have large voltage gain. A cage around the
> terminal would be a curious possibility.
>
> > Also does it not suggest that the terminal size be increased
proportionately
> > to the elevation of the ring -again to prevent arcing or corona?
>
> This would also reduce the voltage gain. Ok if you can add more primary
> capacitance to compensate.
>
> > 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.
>
> The voltage gain decreased.
>
> I am making available a program that designs the directly coupled
> coil and the capacitive transformer version (calculates the elements).
> See at the end of the page about the capacitive transformer coil:
>
> http://www.coe.ufrj.br/~acmq/tesla/mres4ct.html
>
> Antonio Carlos M. de Queiroz
>
>
>
>