Re: Safety gap issues

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

I cannot help but chuckle... the new guy calling Gerry (one of our
best) "wrong".  Your 12kV transformer could indeed output 22.5kV (ya
know that thing called resonance that occurs with series LC circuits?
Better read up on that), but I'm willing to suspect that your gap is
firing at less than 22.5kV (again, depends on geometry... this is one
fact you seem to acknowledge and ignore at the same time?).  Since you
arent using very large spheres as the spark gaps, the 30kv/cm figure
will not apply, because its more likely that your E-field is strongly
non-uniform, allowing premature breakdown.  But as many have
commented, a ruler is no method for measuring voltage!

So, spend a few bucks and buy/build a HV resistive divider and just
MEASURE the voltage (not with tank cap hooked up, but just NST and
spark gap) with a volt meter, preferable one with a 10Meg input
impedance.  If you need advice as to how to make a divider, just ask.
I or many of the other list members have built their own and would be
able to offer up exact parts used.

And JT, please calm down a bit before you embarrass yourself even more
;-).  You seem to  try to call other's bluff before you get the facts
straight, I personally find that insulting.  You are working with
people who have been doing this for years and years, dont forget that.

>From your other post:

"I too have wondered if my calculatioons are way off, but half of my
calculated voltage? Oh god that sucks- a mere 195KV output. Hardly a
tesla coil at all."

Perhaps you are accustomed to hearing those claims of millions of
volts from sparks a few feet in length?  That was before people gained
a true understanding of the physics going on in a tesla coil, those
people were just plain wrong.  Only a rare few tesla coils actually
exceed 1MV output.  Even DC.Cox's big bruiser was said to be measured
at 850kV if i remember, it makes 25 foot sparks:

http://www.tb3.com/tesla/ch2005/pages/IMG_comp.html

Just for reference, that coil is 16-18 feet tall i believe.

Steve Ward

On 11/25/05, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "JT Bowles" <jasotb@xxxxxxxxxxx>
>
> You said:
> "The breakdown for air is approximately 30KV per cm.  This is a local
> field strength and if the field is uniform (constant) then you can
> measure the distance to find the total breakdown.  The 25KV per inch
> you found probably assumes a geometry and applies to a short range of
> distances. "
>
> Well holy crap, that throws ALL my measurements with high voltage off
> a lot. My sparkgap for example is set at 7.5 to 8 mm. That means my
> sparkgap is set at 22.5kV? NO WAY; MY TRANSFORMER OUTPUTS 12KV ONLY.
> SO, IF IT WERE SET AT 22.5 KV, IT WOULDNT FIRE WORTH CRAP.
>
> THIS MEANS THE FORMULA:  1cm=30KV   cannot be correct
>
> Thanks a ton for the help, but I THINK you're wrong buddy
>
>
>
> >From: "Tesla list" <tesla@xxxxxxxxxx>
> >To: tesla@xxxxxxxxxx
> >Subject: Re: Safety gap issues
> >Date: Fri, 25 Nov 2005 08:00:02 -0700
> >
> >Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
> >
> >Hi JT,
> >
> >>Original poster: "JT Bowles" <jasotb@xxxxxxxxxxx>
> >>
> >>Use a counterpoise? You mean putting large amounts of al foil,
> >>spread on the ground, as an RF ground? WTF no way dude, that ruins
> >>the aesthetics of my coil.
> >
> >Counterpoise was for indoor operation.  If you are outdoors and have
> >a rod in the ground, GREAT.  Keep the NST with the coil and ground
> >the NST, secondary base, and strike rail to a common point and run a
> >heavy short wire between this common point and the pipe in the
> >ground (RF ground).
> >Your target for sparks should be grounded to RF ground at the common
> >point (not the pipe end).  This keeps strike return current out of
> >the heavy wire to the pipe and will help keep RF ground noise to a
> >minimum.   Ground your variac and line filter to mains ground.
> >
> >The breakdown for air is approximately 30KV per cm.  This is a local
> >field strength and if the field is uniform (constant) then you can
> >measure the distance to find the total breakdown.  The 25KV per inch
> >you found probably assumes a geometry and applies to a short range
> >of distances.
> >
> >Gerry R.