Re: Safety gap issues

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Jason,

At 03:55 PM 11/27/2005, you wrote:
> YOU SAID:
> "A very good equation that works well to find a coils peak output voltage is:
>
> Vt = Vf x SQRT (Cp / (2 x Cs))
>
> Where:
>
> Vt it the peak top voltage
> Vf is the spark gap firing voltage
> Cp is the primary capacitance
> Cs is the effective secondary capacitance
> SQRT square root function "
>
> * if i know the distance, can you tell me the sparkgap firing 
> voltage? it is 7.5 to 8 mm, at 30MA. 8000v?

Hmmm...  I think you are using copper pipes in your spark gap so we 
will just assume they are about 2.5cm in diameter and use that data 
from this chart:

Hmmm... That gives 25 kV peak which sound way to high for your 12000V 
NST...  It would normally be about 12000 x SQRT(2) = 17kV.  But your 
primary cap is near resonant so maybe you are getting a bit 
more...  Hard to say without a high voltage probe and all...  Lets 
just average the two ;-)

(25 + 17) / 2 = 21kV  That is probably as close of guess as we can 
make from here.  So your coil is firing at about 21kV as far as we can guess...



> * primary capacitance? you mean just the capacitor? 7.8nF (.0078 uF)

Yes.

> * secondary capacitance, with toroid, is 18.6 pF (.0000186 uF)
>
> wtf? that means my coil only makes 117.3KV!!!!?   Cant be true. I wont buy it

Vt = Vf x SQRT(Cp/2Cs) = 21000 x SQRT(7.8e-9 / (2 x 18.6e-12)) = 
304kVpeak.  that is probably pretty close.  If everything we exactly 
perfect, that would give about 32 inch streamers.  I think you said 
that yours are about 16 inches so maybe something is not perfect.

You mentioned 8000 volts for Vf.  That would give:

8000 x SQRT(7.8e-9 / (2 x 18.6e-12)) = 116kVpeak and about 20 inches 
in a perfect system.  It is possible the firing voltage is rather low 
but I would be super careful about trying to raise it.  If something 
else is wrong, raising the firing voltage might blow the NST up...

Most Tesla coils run in the 250 to 500kV peak range.  There are a few 
coils that get past 1 million voltage but they are vary rare.  Here 
is one a little under 2,000,000 volts ;-)

http://www.lod.org/Projects/electrum/testing/pages/Levine23pwr.html

http://www.lod.org/Projects/electrum/index.htm

It is 38 feet tall!!!

Cheers,

        Terry



> > From: "Tesla list" <tesla@xxxxxxxxxx>
> > To: tesla@xxxxxxxxxx
> > Subject: Re: Safety gap issues
> > Date: Sun, 27 Nov 2005 10:02:21 -0700
> >
> > Original poster: Terry Fritz <vardin@xxxxxxxxxxxxxxxxxxxxxxx>
> >
> > Hi,
> >
> > A very good equation that works well to find a coils peak output voltage is:
> >
> > Vt = Vf x SQRT (Cp / (2 x Cs))
> >
> > Where:
> >
> > Vt it the peak top voltage
> > Vf is the spark gap firing voltage
> > Cp is the primary capacitance
> > Cs is the effective secondary capacitance
> > SQRT square root function
> >
> > This assumes the coil is well tuned and running well without any problems.
> > As far as I could ever tell, the size of the toroid really does not 
> > affect voltage that much.  But larger toroids do have larger 
> > streamers.  I think that is do more to electrostatic field effects 
> > rather than higher voltages.
> >
> > Cheers,
> >
> >         Terry