Re: Re[2]: Capacitor Size

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>


The safety gaps in the Terry filter prevent this very problem from occuring.

Dr. Resonance

I disagree on two points.

1) The width of a static gap should NOT be set to
achieve 120BPS.  While I agree that adjusting the
static gap width does permit one to adjust the
BPS to almost any desired value, it ignores the
most important consideration in setting gap
width.  The width must be such that the breakdown
voltage does not exceed what's safe for the
NST.  In my earlier post today where I cited
measured BPS measurements for my mini coil, the
BPS was between 157 and 257, depending on the
tank cap size.  The gap width was fixed and had
been set by connecting only the NST to the gap
and adjusting it just wider than where it began
to arc.  Had I adjusted the gap wider still to
where the BPS measured 120, it would have been
operating at a higher and unsafe bang voltage.

It's not clear what voltage you consider the plus
and minus peaks to be.  Depending upon how close
to mains-resonant the cap is and if you're
saturating the NST core, mains-resonance will
occur to varying degrees.  If it didn't, nothing
would happen when the Variac was at 50%.  The
point is, the NST & cap will achieve 60 Hz
resonant rise to the point of the gap breakdown
voltage, and if the gap is set to 30kV, a 15kV
NST can easily ring up to that.  So it's not like
a 15kV NST can't charge a cap to greater than
SQRT(2)*15kV and that's what the gap must be set for.

2) A static gap firing more than 120 times per
second is not uncommon, it's the norm.  I base
this opinion on scope measurements of my
coils.  On what do you base your opinion?

Think of it another way.  For any given NST size,
the recommended cap size for a 120BPS sync gap is
about twice the value as for an LTR static
gap.  The goal for both cases is to achieve the
largest bang as is safe, so the bang voltage must
be comparable.  If both cases are to process
comparable amounts of power, the only way the
static gap can do so with a cap half as big is to fire twice as often.

Regards, Gary Lau
MA, USA




> Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>
>
> It's done with the setting (distance) of the
> spark gap itself.  It is adjusted such that the
> gap can only fire when the AC waveform hits its
> plus and minus peaks, thus insuring it fires at
> 120 pps.  We usually use 7-8 5/8 inch dia. tubes
> with a total gap setting of 0.310 inch (divide
> this by the number of gaps in your system).  We
> use a 90 cfm fan to blow thru the 6 inch ID PVC
> tube.  This works fine up to 120 ma.
>
> If the gap is set too close together it could
> re-fire more than 120 times per sec but this is uncommon.
>
> Dr. Resonance
>
>
> Is there a formula to calculate the BPS of a SSG?
>
>
> I'm curious, what speed did you measure?
>
> Best regards,
>
> Sebas.
>
>
> Thursday, October 6, 2005, 10:08:55 PM, you wrote:
>
>
>  > Original poster: "Lau, Gary" <<mailto:Gary.Lau@xxxxxx>Gary.Lau@xxxxxx>
>
>
>  > Hi DC:
>
>
>  > I assume you meant to say "0.016 at 60 mA".
>
>
>  > Have you actually scoped a coil with a static gap
>
>  > that operates at 120 BPS? Every static gap coil
>
>  > that I've scoped ran at a far higher rate than
>
>  > that.  I probably could have achieved 120
>
>  > (chaotic average) BPS, but I would have had to
>
>  > open the gap to an unsafe setting.  Since I tend
>
>  > to use a 2X mains-resonant cap size, I would see
>
>  > an even higher BPS had I used a 1.57X cap.
>
>
>  > In my early naïve days of coiling I thought that
>
>  > 120 BPS was the natural and normal mode of
>
>  > operation for a static gap.  I know better now
>
>  > and don't wish to perpetuate that misunderstanding.
>
>
>  > Regards, Gary Lau
>
>  > MA, USA
>
>
>
>   >> Original poster: "D.C. Cox"
> <<mailto:resonance@xxxxxxxxxx>resonance@xxxxxxxxxx>
>
>
>
>
>
>   >> Erms resonant value times 1.57 for best effective C value.  With 30
>
>   >> mA its near .008 and doubles to 0.16 at 60 mA.  This works best with
>
>   >> a static copper tube sparkgap firing 120 pps.
>
>
>   >> Dr. Resonance
>
>
>
>
>
>   >> >Original poster: "Lau, Gary"
> <<mailto:Gary.Lau@xxxxxx>Gary.Lau@xxxxxx>
>
>   >> >
>
>   >> >The mains-resonant cap value for a 15/30 NST with 60 Hz power is
>
>   >> >.0053uF.  It was once thought that this would hit a performance
>
>   >> >sweet-spot, but I don't think this is so.  Non-linear behavior
>
>   >> >(ferroresonance) of the NST core makes the mains-resonant cap value a
>
>   >> >moving target.
>
>   >> >
>
>   >> >The rage these days is to use a Larger
Than (mains) Resonant cap value.
>
>   >> >The calculated mains-resonant value multiplied by the square root of 2
>
>   >> >(or was it 3?) is often cited as the optimum value.  Personally, I've
>
>   >> >found that 2X the mains-resonant value
works well.  I doubt there's any
>
>   >> >kind of sharp sweet spot, so any of these factors will all work.
>
>   >> >
>
>   >> >One thing that is clear is that streamer
length is proportional to bang
>
>   >> >size.  So if your static gap fixes the bang voltage, you can get a
>
>   >> >bigger bang and longer streamers at a reduced bang interval by using a
>
>   >> >bigger cap.  But if your wife favors
your existing cap, you might get a
>
>   >> >bigger ba...  OK, I'll stop there.  Always a compromise...
>
>   >> >
>
>   >> >Regards, Gary Lau
>
>   >> >MA, USA
>
>   >> >
>
>   >> >
>
>   >> >
>
>   >> > > Original poster: "Dirk Stubbs"
> <<mailto:dirk@xxxxxxxxxxxxxx>dirk@xxxxxxxxxxxxxx>
>
>   >> > >
>
>   >> > > I have a question about sizing of a capacitor. My power supply is a
>
>   >> > > NST 15kV at 30mA. I originally planned on using 10 doorknob
>
>   >> > > capacitors which are rated at 30kV with 0.006 uF total(each was 620
>
>   >> > > pF). However I have a question about the needed capacitance for my
>
>   >> > > TC. Most of the references such as websites  and calculators said
>
>   >> > > that I need .0053 but I see people saying you need .008-.009 uF.
>
>   >> > >
>
>   >> > > What size is correct?
>
>   >> > >
>
>   >> > >
>
>   >> > > What will happen if I use my current capacitor setup?
>
>   >> > >
>
>   >> > >
>
>   >> > >
>
>   >> > > I would like to use my current setup to save money. The wife has
>
>   >> > > about had it with the TC as it is . J
>
>   >> > >
>
>   >> > >
>
>   >> > >
>
>   >> > >
>
>   >> > > Thanks,
>
>   >> > > Dirk
>
>   >> > >
>
>   >> > > -
>
>   >> > >
>
>   >> >
>
>   >> >
>
>
>   >>
>
>
>
>
>
>
> --
>
> Best regards,
>
> Sebastiaan
>
>
>