Re: Safety Gap

["Tesla list" <tesla-at-pupman-dot-com>]

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

Hi Luke,

Actually, Javatc gives you the answer to the pipe gap question. Click on 
the "help" next to the inputs (the text is in BOLD font). Multi-segment 
pipe gaps are another one of those areas where the arc voltage is probably 
going to fall off. If only two pipes, then it will be a better 
approximation, but as the number of pipes increase, so does the deviation. 
The reason is simply the greater number of variables. Even if someone here 
performed a multi-segment pipe gap breakdown test (as Dr. R did with the 
flat electrodes), the next person who built a similar gap may have 
completely different breakdown voltages. The pipe diameter, the pipe ends 
(sharp, rounded, etc), how truly parallel the gaps are, the number of 
pipes, etc.. etc.. Just a lot of variables. Even with the simply 2 
electrode static gap, there will be some deviation (temp, barometric 
pressure, etc., minute surface features, ROC, all those little subtleties 
add up).

There just haven't been enough real breakdown testing passed to the list. 
This is for all types of commonly used spark gaps. It's fine to theorize, 
but in my mind, only real breakdown test with the commonly used spark gaps 
can allow us to closely approximate the breakdown voltages (and we are in 
need of that information). I plan to do my own testing this year and 
purchased a transformer for this purpose. Javatc isn't going to help much 
with multisegment static gaps or with needle gaps.

On your second questions, the two small point electrodes would work as a 
safety gap as long as the distance exceeded the main gaps breakdown. 
However, should the safety gap fire, the small ends may heat up 
substantially from the lack of material. The heat would cause lower 
breakdown and you may end up with the safety gap taking over (and probably 
burning up if it does).

I have used horn gaps in the past that worked fine, but the wire size was 
like #6 solid copper.

Take care,
Bart

Tesla list wrote:

>Original poster: "Luke" <Bluu-at-cox-dot-net>
>The gap I used was not for use as the safety gap. I was just trying to
>get an idea as to what spacing I did need for the gap. I knew shape had
>a little to do with it but didn’t think that much.
>
>But for the sake of getting the feel of it, let me ask this.
>
>If I were to use
>1: standard style main static spark gap consisting of copper pipe
>parallel to each other and spaced at about 0.29" as JavaTC says is about
>right.
>
>2: Used a needle gap for a safety gap set at just over 3/4" so gap
>was just large enough to prevent the NST from arcing.
>
>Would the safety gap still perform its task?
>I would assume yes but what are some thoughts on this.
>I do intend to use rounded electrodes in the safety gap but what would
>be the input on the above?
>
>Luke Galyan
>Bluu-at-cox-dot-net
>
>-----Original Message-----
>From: Tesla list [mailto:tesla-at-pupman-dot-com]
>Sent: Saturday, February 07, 2004 3:35 PM
>To: tesla-at-pupman-dot-com
>Subject: Re: Safety Gap
>
>Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
>
>Hi Luke,
>
>Absolutely! What you basically have is a needle gap. The influence of
>electrode shape and size plays a major role defining the arc voltage for
>a
>given gap width. For larger electrodes and the narrow gap spacing used
>for
>the typical spark gap configuration, the numbers should be pretty close.
>
>The reason is that the electrodes appear planar. But as you start
>decreasing the electrode size where the gap width is larger than the
>electrode size, the shape and curvature come into play. And with that,
>if
>the gap width is "much" larger, the electrodes begin to appear like a
>point
>or needle gap.
>
>Dr. Resonance last year tested flat electrodes with a 30kV supply
>varying
>the gap width and measuring the voltage at which the gap conducted.
>Javatc
>follows those actual arc voltage measurements pretty darn close
>throughout
>it's range. Thanks to Dr. R's measurements, I had some actual data to
>work
>with. However, if a needle gap such as you have set up is used, then all
>
>bets are off. However, what you have provided here is another good piece
>of
>information that can be jotted down for review regarding a needle gap
>setup
>with a 15/30 NST could arc across 3/4", which is certainly believable.
>
>Take care,
>Bart
>
>Tesla list wrote:
>
> >Original poster: "Luke" <Bluu-at-cox-dot-net>
> >Yup no caps.
> >Just an NST and a Spark gap.
> >The spark gap in this case was nothing more than two pieces of copper
> >wire cut and pointed toward eachother. So it wasn’t rounded balls or
> >anything like that. Does that make a huge difference?
> >
> >Luke Galyan
> >Bluu-at-cox-dot-net
> >
> >-----Original Message-----
> >From: Tesla list [mailto:tesla-at-pupman-dot-com]
> >Sent: Friday, February 06, 2004 6:34 PM
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Safety Gap
> >
> >Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
> >
> >Hi Luke,
> >
> >What are using as electrodes and what are the dimensions of the
> >electrodes?
> >BTW, is this test with only the NST and the sparkgap? (no cap in
> >there?).
> >
> >Let me know.
> >Thanks,
> >Bart
> >
> >Tesla list wrote:
> >
> > >Original poster: "Luke" <Bluu-at-cox-dot-net>
> > >I was working out how I wanted to make my safety gap and happened
> >across
> > >something that has me confused.
> > >Using the JavaTC program with a static spark gap and a 15KV NST, if I
> >set
> > >the total gap spacing to anything over 0.3” I am informed that the
> >voltage
> > >needed to jump the gap is greater than the peak voltage of the NST.
> > >
> > >I was assuming that the safety gap would be set at close to this
> >distance
> > >as well. I started playing with a 15KV 30mA NST. I can set a gap of
> >almost
> > >¾” and still get an arc when I energize the NST. This seems to be
>close
> >to
> > >the cut off point since it sometimes will and sometimes will not jump
> >the
> > >¾” gap.
> > >
> > >Yes I know the peak voltage is around 21 or 22KV. And just to avoid
>the
> >
> > >questions no I am not using a variac. I just have a cord with a cord
> >cap
> > >on it and I plug it in, then poof an arc jumps the ¾”.
> > >
> > >Is JavaTC telling me something other than what I think it is? Is
>there
> > >something I am missing? Any comments.
> > >
> > >Luke Galyan
> > >Bluu-at-cox-dot-net
> > >
> > >
> > >
> > >
> > >
> >
> >
> >
> >
>
>
>
>