Re: 3/4, 1/4, or 3/4 copper tubing? Is a Strike Rail needed?

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Terry,

On 4 Nov 2002, at 8:15, Tesla list wrote:

 > Original poster: "Terry Blake by way of Terry Fritz 
<twftesla-at-qwest-dot-net>" <tb3-at-att-dot-net>
 >
 > Hi Adam,
 >
 > I have not used a strike rail yet, but I am thinking about it.  I have not
 > had anything bad happen, but when my primary gets hit, it tends to fire the
 > safety gaps.  That bugs me for two reasons;
 >
 > 1) I have to back off the power to quench the gap
 >       (maybe I should use one of those horn gaps).
 > 2) There is clearly a surge going to my transformer. That makes me worry.
 >
 > Here is my HUGE coil primary taking a hit.
 > http://tb3.phpwebhosting-dot-com/tesla/hugecoil/powerup2/P6280028.jpg
 >
 > Here are the filters and safty gaps.
 > http://tb3.phpwebhosting-dot-com/tesla/hugecoil/powerup2/P6290024.jpg
 >
 > Here is all about my HUGE coil.
 > http://www.tb3-dot-com/tesla/hugecoil/hugecoil.html
 >
 > I guess if you have protection for your transformers, it may not be a
 > problem.  But it is relatively easy to add this protection.  My real concern
 > is when I take a hit to my secondary.  That really hurts.
 >
 > What do other people have to say about the strike rail?

Following past list discussions, I think there is a general concensus
that if the coil is inclined to send arcs to the primary, a strike
rail is a good idea. The reason is not obvious but intuition shows it
to be valid. What happens is that a common mode spike races back
towards the transformer terminals elevating *both* momentarily,
compromising insulation between the transformer secondary and primary
and/or core.
     A lot would depend in the electrical layout of the primary system
- whether one side of it is grounded and to which ground (RF or
mains) for example. If one side is  grounded, then the spike may put
a high differential voltage across the transformer secondary (higher
than the cap firing voltage) depending on which part of the primary
is grounded and/or hit.
      If you have a primary gap that is firing correctly and a safety
gap rigged up, you can, under the "right" circumstances, see the
safety gap firing with quite low energy sparks indicating that it is
not the primary cap overvolting. Long leads between the transformer
and Tesla primary are a good way to boost such voltages as are
"filter" chokes. With the risetimes involved, these components can
act like transmission lines and little Tesla secondaries all by
themselves. I lost a NST about 8 years ago observing all this. A year
later, I had to partially rewind an entirely different transformer
running with long leads the the primary gap and tank circuit which up
until that time, had been used with connecting leads only a couple of
feet long and never had a problem previously.

Regards,
Malcolm






 > Terry Blake
 > Coiling in Chicago.
 >
 >
 > ----- Original Message -----
 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > To: <tesla-at-pupman-dot-com>
 > Sent: Sunday, November 03, 2002 2:35 PM
 > Subject: Re: 3/4, 1/4, or 3/4 copper tubing?
 >
 >
 >  > Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
 > <dhmccauley-at-spacecatlighting-dot-com>
 >  >
 >  >  > I am in the process of building my new coil, but wondering if I should
 > use
 >  >  > 1/4, 1/2, or 3/4 inch copper tubing for my primary. My power supply
 > will
 >  > be
 >  >  > 2 12/60 nst's (1440W). Also, what size tubing should I use for my 
spark
 >  > rail?
 >  >  > Thanks
 >  >  > Adam
 >  >
 >  >
 >  > You'll get a lot of different opinions on this, but 1/4" copper tubing
 >  > should be just fine.  I run two (2) 15kV/60mA NSTs using only a
 >  > 1/4" copper tubing and it barely gets warm even during long run periods.
 >  >
 >  > Strike rail???  A strike is good for looks.  Functionally, its basically
 >  > worthless in my opinion.   In my experience, the same people claiming you
 >  > need
 >  > a ground system consisting of six hundred, geometrically spaced, 20 foot
 >  > rods in the earth are the same people who are going to tell you you need
 >  > a strike rail.
 >  >
 >  > Heck, my grounding system now is just tying my braided rf ground lead 
with
 > a
 >  > single loose-fitting overhand knot around my gas line going into my 
house.
 >  > Works great!!!!
 >  >
 >  > Dan
 >  >
 >  >
 >
 >
 >