Re: Res cap size charge

```Original poster: Bart Anderson <classi6-at-classictesla-dot-com>

While the gap conducting?
The ringdown following quench maybe.

Take care,
Bart

Tesla list wrote:

>Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
>
>You would also have to take into consideration capacitor charging due to
>reflected energy since in most coils first notch quenching isn't happening.
>The energy coming back across the spark gap due to the collapsing sec
>magnetic field would certainly make for faster cap charging than is
>predicted by the classic 5RC value.
>
>Dr. Resonance
>
>Resonance Research Corporation
>Baraboo   WI   53913
> >
> > I guess I have to disagree. The time constant doesn't fall apart. The time
> > constant is very relevant to cap and transformer selection for breaking at
> > a particular rate at a particular voltage. The voltage at any point in
>time
> > can be derived with the time constant. Yes, of course the voltage is
> > changing (it's AC). The time constant isn't based on the voltage, it is
> > based on the capacitance and impedance. For accuracy, it helps to compute
> > the complex impedance, but even a bulk impedance is very helpful.
> > Regardless, it's "when" to look at the time constant that is relevant and
> > helpful. The breakrate is an obvious time to look. Suppose I had a cap of
> > 5uF and used a little 9/30 NST to fire across a 9kV gap at 120 bps? The
> > answer via the rc time constant (and in real life) is "you can't" because
> > the voltage is only 71 volts at the cap. It's the time constant that makes
> > this information available before you go to all trouble only to find out
> > had you equated the cap voltage in the first place, you would have seen
> > that 71 volts isn't going to do much for you.
> >
> > This is how the time constant is "useful". Yes, there may be issues with
> > resonant rise, inductive kick, but when that is the case, the complex
> > impedance in those situations must be used for precision numbers, but even
> > a close approximation is still very useful in the design stage.
> >
> > Take care,
> > Bart
> >
> > Tesla list wrote:
> >
> > >Original poster: "Luke" <Bluu-at-cox-dot-net>
> > >
> > >I was looking around the list archives and making up a spread sheet for
> > >joules of the cap after charge time of 1/4 cycle and voltage on the cap
> > >and number of rc time constants in the 14 cycle etc............
> > >
> > >When I ran across a post on the archives pointing out the obvious. :(
> > >The voltage is always changing so the rc time constant thing kind of
> > >falls apart.
> > >
> > >Thanx for the info.
> > >
> > >
> > >Looking at the infor on the first link you sent I ran across something I
> > >would like some opinions on.
> > >
> > >Seems a good value for c would be 1.357 times c res.
> > >That is where you hit the 120bps mark.  Going below this obviously gets
> > >too close to c res and going above this slowes down the bps while also
> > >giving less real power on the cap.   Why is the rule of thumb them 1.6
> > >times c res for a static gap?
> > >Luke Galyan
> > >Bluu-at-cox-dot-net
> > >
> > >-----Original Message-----
> > >From: Tesla list [mailto:tesla-at-pupman-dot-com]
> > >Sent: Wednesday, January 21, 2004 7:29 PM
> > >To: tesla-at-pupman-dot-com
> > >Subject: Re: Res cap size charge
> > >
> > >Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
> > >
> > >Hi Luke,
> > >
> > >At 06:41 PM 1/21/2004, you wrote:
> > > >I know it is not recommended to use a resonant size cap and that is not
> > >my
> > > >intent.
> > > >
> > > >Using ohms law for the impedance of an NST of 15KV 60mA gives 250k ohms
> > > >Using the capacitive reactance formula there the capacitance at 60Hz is
> > >
> > > >0.0106mfd
> > >
> > >Yes.
> > >
> > > >
> > > >Using 250k ohms and 0.0106mfd the RC time constant would be 2.65ms
> > > >Since the time to charge a cap is ¼ of the wave the time for cap
> > >charging
> > > >at 60Hz is 4.17ms.
> > >
> > >Nope.  It get's real messy now...  Although the time constant thing
> > >gives
> > >sort of comfortable numbers at first.  It is all screwed up in this
> > >case.
> > >
> > > >This works out to the cap going through 1.57 RC time constants for each
> > >
> > > >charge cycle.
> > > >This is about 75% charged and 75% of 15KV is 11.2KV.
> > > >
> > > >So using a resonant sized cap will give max voltage of 75% (11.2KV in
> > >this
> > > >case).
> > > >
> > > >Does this mean setting the spark gap (static) to fire at 11.2KV would
> > >give
> > > >the same voltage to the system as if the gap were set to fire at 15kv?
> > > >Since the 15kv from the NST would fire the gap but only 11.2KV would
> > > >discharge from the cap into the primary.
> > > >
> > > >I know that the amount of energy is not the same as the amount of
> > > >voltage.  Energy is will be related to joules which is dependent on
> > >both
> > > >voltage and cap size.  I am only talking about the amount of voltage
> > > >present not the amount of energy.
> > >
> > >When F = 1/ (2 x pi x QSRT (L x C)) , or, 250k = 1 / (2 x pi x 60 x
> > >C),  all kinds of factors start dividing out and things "theoretically"
> > >get
> > >explosive as infinite amounts of energy are transferred.  But in
> > >reality,
> > >resistances and losses keep the mess under theoretical control.  At that
> > >
> > >point, simple equations we learned at school start to fall down and we
> > >need
> > >to crank the mess through the computer to get results that reflect the
> > >"real world".  Here is a nice thing that deals with all this here, that
> > >a
> > >surprising amount of theory is based on, but nobody realizes it :o)))
> > >
> > >http://hot-streamer-dot-com/TeslaCoils/Misc/NSTStudy/NSTStudy.htm
> > >
> > >You "might" also want to see:
> > >
> > >http://hot-streamer-dot-com/TeslaCoils/OtherPapers/TeroRanta/CurrentLimitedT
> > >ransformers/NSTModel.htm
> > >
> > >http://hot-streamer-dot-com/TeslaCoils/OtherPapers/TeroRanta/NSTCapMatching/
> > >ResonantCapacitorMatch.htm
> > >
> > >but this is getting into areas that makes my brain hurt too -at-:o)))
> > >
> > >Cheers,
> > >
> > >          Terry
> > >
> > >
> > >
> > > >
> > > >Luke Galyan
> > > >Bluu-at-cox-dot-net
> > > >
> > >
> > >
> > >
> > >
> >
> >
> >
> >
>
>
>
>

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