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=?iso-8859-1?Q?Re:_Ed=B4s_Amps_(was_cap_failure...)?=
Tesla List wrote:
>
> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
>
> Hello Ed, All
>
> You wrote:
>
> >Original Poster: Ed Phillips <evp-at-pacbell-dot-net>
> >
> >Example:
> >
> > The reactance of an 0.1 mfd capacitor at 100 kHz is about about 16
> >ohms; if the Q is 100, the ESR will be about 0.16 ohms. If the RMS
> >current in the circuit is 100 amps (a pretty high value), the total
> >power loss due to ESR would be 160 watts. This shouldn't heat a
> massive capacitor very fast. Real high-power experts - comments please.
>
> Why do you say 100 amps of primary current is a lot? I would say this
> is pretty low for coiling circuits:
>
> I am presently running:
>
> 1.) a 25.5nF cap
> 2.) a 7.5kV/75mA NST
> 3.) Primary inductance is:37.85µH
>
> Eq1:) J=0.5*C*V^2
> Eq2:) J=0.5 *L*A^2
>
> solving for A:
>
> A = V* SQRT(C/L)
>
> Vgap=7500*1.414 (peak V)
> Lpri=37.85µH
>
> A = 10606 * sqrt ((25.5*10^-9F)/(27.85*10^-6H))
> = 10606 * sqrt(9.15*10^-4)
> = 320.8 Amps
>
> With a 7.5kV 75mA NST, I am certainly not running a high power coil.
> My arc length is around 41". My final setup will be running 4500VA worth
> of 7.5kV NSTs and a 100-120nF cap into a primary designed to resonate at
> ~98Khz. A rough calculation leads to around 1.5kA for this design.
> So, I would DEFINATELY NOT consider 100A of primary current "big".
>
> BTW:
> My arc length pretty much fits John Freau´s calculation of spark length
> = SQRT(VA)*1.7. This would be 53" in my case (not quite there yet).
> On the other hand 41" is ceiling heigth at the moment (so I don´t know
> if the arcs might be longer) and I am not running the max primary cap
> possible (which would be around 32nF). And my toroid is too small
> (4.3" x 10"). I get multiple streamers all the time. There is no pointed
> object necessary to provide breakout. I get a 41" roughly every 15-30
> secs of run time. These 41" discharges are white hot.
>
> This once again leads me to believe a low voltage high current design
> does NOT lose against a high voltage low current (of the same VA)
> design.
>
> Coiler greets from germany,
> Reinhard
I agree with you. Intended to say that 100 amps was a pretty
conservative number for the value during the discharge cycle. My coil
here is also small, runs from a 12 kV 60 ma NST, and uses an 0.01 mfd
primary capacitor. Assuming it charges only to the RMS secondary
voltage before the gap fires, that gives a current of about 300+ amps
during the first part of each discharge. The discharge rate is of the
order of only 240 per second, however, so the net RMS current over any
set of charge/discharge cycles is no where near that high. I'm too lazy
to figure it out, but know that the primary (which is wound with #10
solid wire) doesn't even get hot after minutes of running.
Ed