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RE: Geek Pig! :)



Original poster: "David Dean by way of Terry Fritz <twftesla-at-uswest-dot-net>" <deano-at-corridor-dot-net>

Hi

> >I have used a pig to power a 2 3/4 inch dia. coil before, and
> normally is
> >it
> >for my four inch coil.
> >
>
> That's quite a bit of overkill isn't it?

Well...The 2 3/4 " sec didn't last very long, it had a splice about 1/3 the
way up the coil and the solder blew off. I have blown solder off the top and
the bottom connections on the 4" coil before too, but have it fixed now so
that can't happen. Actually the pig can be used just like a NST at lower
power levels with proper ballasting. The 4" coil will deliver 39 to 40"
streamers at about 1.2KVA and hit 60" at just over 2KVA. When you use a sync
rotary spark gap you can not put in more energy than the 0.5C*V^2*BPS and
the V depends on the voltage the transformer can develop, at the peak, and
the firing position or angle. With a 48nF cap I was able to get one long
spark 80" by the tape measure, but 60" is about the reliable limit for that
coil. The winding length is 20".

>
> Is it possible to toast a secondary with that much power? I would
> think it
> would damage it easily.
>

The thing is that just because a transformer is rated 5KVA (mine) or 10KVA
(yours) does not mean that it has to deliver that much power. Sure I could
over power my coil, but to do that I would have to increase the BPS or the
bang size. The bang size is fixed by the cap size for a given voltage. That
is another advantage to running a small coil with a pig instead of a NST,
you don't get the resonant rise thing going unless you get into the range
with the primary ballast.  As it is I can not get enough ballast to reduce
the gap losses with what I have (small cracker box welder) when using the
smaller caps. When I use the 48nF cap things start to get better for the
gap, but I have to limit the voltage to stay in range for the power handling
of the coil. If you have the coupling and the tuning set right then you
really do not have much to worry about as far as destroying a secondary. If
you get too much power in, then you get too long streamers and they start
striking the primary and anything else they can find.


> Where can I get a variac big enough for this beast? I can't find them
> locally so I'll have to get one donated...how big do I need? I'm hoping I
> don't have to hunt down a full 50A...but I have a feeling I will.
>
I have no Ideas about that. I did run for the first year I had the pig
without a variac with no problems. It is just a bit wild to tune with only
full power available.
>
> > > We also got 3 large 12kV lightning arrestors (they're about 6"dia and
> >18"
> > > tall) and 2 small ones (the usual ones, about 3"dia and 10"
> > > long), plus some
> > > HV switchgear for our Project Thumper and the (as yet unnamed) Marx
> >bank.
>
> The Marx bank is now named Project Groucho (yes, really)
>
> Can the smaller (3"dia X 10"L) 12kV arrestors be used for
> protection of the
> Pig?
> Do Pigs NEED protection?

Not really, at least at reasonable power levels.


 The Lightning arrestors we have are all rated at
> 12kV, but the Pig is rated at 13.8 and I KNOW the arrestors were
> hooked up
> to it when in service. What is the actual firing voltage of the arrestor?
> Does anyone know the internal construction of the arrestors?
> Especially the
> large ones (about 6"dia X 18"L), they are a large grey ceramic insulator
> with the bottom  having much smaller ribs and encased in a 4"
> deep aluminum
> base. Mounting is by 3 bolts on the bottom. There is something akin to
> Creosote holding it in place and sealing it to the base. It's black,
> brittle, Glass like....but has a bad-smelling powder when beat on
> or filed.
> I need a Dremel.....I can accomplish anything with a Dremel and the right
> bit.....:)
>
> >What is the high voltage rating? 7.2? 14.4? switched? other?
>
> 13.8kV at 10kVA, 208 Lbs
>
> >Yes. Put 240V into the outer two bushings, with adequate current
> limiting
> >of
> >course, and remove the strap from the center bushing. Be sure to
> check the
> >LV windings with an Ohmmeter after removing the strap to make
> sure there is
> >no continuity to the case. Leave the center terminal N.C.. To use the
> >single
> >bushing pig with a Tesla coil, connect the case to RF ground, also the
> >inside turn of the primary to RF ground.
>
>
> Ok....you want me to make a direct connection between my primary coil's
> inner turn and the base of my secondary? i.e. have them BOTH going to RF
> ground?

Yep.

> Doing so I've JUST made something akin to an Oudin coil haven't
> I?

Nope. An Oudin coil would be made by connecting the bottom turn of the
secondary to the HOT end of the primary. Like an autotransformer. There all
the high freq high voltage is connected directly to the 60Hz sec. of the
high voltage transformer. Some will pass to ground through the primary coil
itself, but some will try to go through the secondary coil of the HV
transformer and though attenuated by the higher inductances there, will tend
to couple back into the primary of the HV transformer thereby increasing the
load on the filter (mains) and increasing the risk of getting HVHF into the
mains, the operator, whatever. Also if one were to be hit by a secondary
streamer the output of the HV transformer would have a direct path through
the secondary coil and the streamer to the - well, in this case let us just
say victim.

> Or have
> I just induced a nice 60hz harmonic into the (now deadly) output of the
> coil?

I would consider the output potentially deadly anyway. And you really
haven't added anything to the secondary, ground is still ground. It would be
safer than leaving the case of the pig floating.

> This doesn't make any sense.....please explain. Because to my
> (and my still
> learning brain) connecting the pig case, and primary coil inner
> turn to RF
> ground (i.e. the same wire that runs outside (or to the cage)) and to the
> base of my sec, is a bad thing.
>

By cage you mean Faraday cage? Are you saying that you connect the base of
the secondary to the same ground as the cage itself? That could be
problematic in itself. The base currents are reported to be quite high (I
haven't tried to measure) and any impedance in the conductor or connections
or even the impedance of the grounding system itself could result in
relatively high voltages being produced. That could result in a potential
difference between the cage and any other grounded object which might happen
to be connected to a different ground. I guess it depends on what the cage
is for. If it is there to suppress RFI then the ground to the same RF ground
as the coil might be the best way to go. But if the cage is there for the
safety of spectators, etc. as in to prevent a shock hazard, _I_ would think
that it should have its own ground, or be connected to mains ground, or
something like that, but not to the same RF ground as the coil. That is
something that I have never used, or given much thought about, so I will
just leave it for those with some real life experience to deal with.

> Hey....it WOULD stop the arcing problem though....at least I think it
> would......hmmmmmmmmm
>
>
> The high voltage output from the
> >bushing to one end of the tank cap, the other end of the cap to the outer
> >tap on the primary coil. The spark gap of course connects
> between the high
> >voltage bushing to tank cap connection and ground.
> >
> >ASCII ART follows, use fixed width font (courier) to view:
> >
> >                         Cap
> >    *------------*--------||------*
> >    |            |                |
> >   pig           0                3
> >   HV     spark     gap           3 TC pri.
> >   out           0                3
> >    |            |                |
> >    *------------*----------------*
> >                 |
> >                ===
> >                 - RF ground
> >
>
> It came out here :)
>
> Looks great...feels wrong.
>
> Christopher A. Boden Geek#1
> President / C.E.O. / Alpha Geek
> The Geek Group
> www.thegeekgroup-dot-org
> Because the Geek shall inherit the Earth!
>
>
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