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Re: Grounding. Oh joy.

Yuri

I have heard this method and I think there is a slight misunderstanding
here - the plate is not actually on the *base* of the secondary, which
would indeed be a disastrous shorted turn. It is a small piece of copper
foil glued to the side of the secondary, but before you do this you hammer
out the base secondary wire until it is thin and flat, solder this to the
foil, and then sand the form to provide some 'key' and epoxy this plate in
place. Then a grounding strap or wire can be attached simply with a rubber
band - makes for a high current connection that is easy to remove - Richard
Quick's idea, if I'm not mistaken.

I don't think we should underestimate base currents on a secondary. As I
have heard, they can be several amps up to tens of amps (I am sure that
there must be some heavy transient peaks as well, especially where coupling
is high.) At such currents the base of your secondary is going to be
elevated to fairly high potentials if your RF ground is more than a few
hundred ohms, and this could spell bad news for the secondary! R. Quick's
work on counterpoises show that an inadequately sized counterpoise (ie 3-4
feet square) is overwhelmed at not much more than 1kW input, and a little
higher than this causes heavy, high-current discharges to the ground under
the elevated ground plane, and at this point the top discharges stopped
growing no matter how much more power was put into the system. I have
noticed a great difference in performance between a poor ground (outside
standpipe only) and four buried ground rods and a large conterpoise of alu
foil laid in a star shape on the ground. My discharge increased nearly 1
foot when I added this 'bottom load'. A big counterpoise on its own is
effective, but for safety's sake you should still connect this to true
earth, poor or otherwise.

The problem with waterpipes indoors (and even outdoors) is that you never
know if the metal pipe extends all the way into the ground itself - with
modern building techniques much more plastic is being used. You could
basically be setting up a huge antenna to radiate vast amounts of RFI
around your house and your neigbours. Cue some heavy bangs on your front
door....

I would say that the iron well lining would be an incredibly good ground -
the combined effects of the huge surface area and the wet earth and rock
should make for a *very* good ground. I would kill to have something like
this in my garden! The corrosion of the iron may even enhance this - the
soil around the well is probably heavily doped with Ferric salts, reducing
resistance even further. *Go* for this one - make a heavy connection with
flat copper strap (cleaning all corrosion off the iron first) and you will
have something special - and hopefully big sparks!

good luck

Alex Crow


----------
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: Grounding. Oh joy.
Date: 24 July 1999 00:35

Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>

Hi Yuri,

At 12:36 PM 7/23/99 -0700, you wrote:
>1. I have heard that it can be a good idea to epoxy a flat piece of copper

>to the base of a secondary to serve as a ground terminal. Would a piece of

>aluminum tape work also?

I have not heard this.  Be carful not to make a shorted turn that would
look like a short circuit and drain power from the primary to secondary
coupling system.  I have heard of using a thick copper strap at the base of
the secondary as a nice connection point but those are never complete
loops.  Apparently, top terminals that form a solid loop are far enough
away from the fields not to have much problem with the shorted turn effect.

I would skip this copper plate thing.  Sounds like a load of trouble...

>2. I have heard that I can use something vaguely like chicken wire called
RF 
>Grounding Strap to ground the secondary. Where do I get this? THe local 
>hardware store? Home Depot? Or the ends of the Earth?

Chicken wire may have some use for building a Faraday cage to contain the
RF noise, but as a grounding wire, it would be terrible.  Thick copper
strap, Litz wire, the braid from a coax cable (not super good) all work
well.  However I just use 14 gauge wire and it seems to work fine for me...
 I just got a roll of Litz so I'll probably change to that now.

Perhaps they meant to put the chicken wire on the floor as a ground plane
for the coil?

>3. I have heard that I should not ground the secondary to a water pipe.
Why? 
>I'd like to know, because I don't feel like diging a six-foot-hole when 
>there is an iron well in the backyard that goes a whole lot deeper than
six 
>feet.

As long as you are sure the water pipe goes straight out into the ground
from where you connect to, it should be an excellent ground.  Hot water
pipes are usually insulated at the water heater to prevent electrolysis
effects from eating up the heater so hot water pipes are very bad.  There
is a chance that your house wiring is grounded to the cold water pipe too
(mine is) so RF could get into the AC.  However, I don't seem to have a
problem with it.  The iron well would work fine too.  Any conductor that is
in good contact with the round should do fine.  The current is low, it is
at RF frequencies, and the voltage is high so grounding a TC is fairly easy
compared to some things.  Any lighting or standard ground rod should do
fine.  If you system is really high power you may want more...

>
>4. I have heard of coils "failing" when they are not properly grounded. Is

>this failing as in "not doing anything," or as in "blowing up beyond all 
>hope of repair and forcing me to wind another three pounds of magnet wire
on 
>another ten dollar PVC pipe?"

It the secondary were not grounded, the same high voltage at the top of the
coil could appear at the loose end on the bottom.  This could cause a power
arc from the primary to the secondary.  If a streamer were to hit a
grounded object at this time the damage could be great.  It could also
present a fairly dangerous electrical path.  All this could occur if there
were NO ground.  However, even a "poor" ground should prevent this.  A poor
ground typically diminishes the output power and adds to RF noise to the TV
and such...

>
>Thanks for advice.
>
>-Yuri Markov
>Who has heard



Cheers,

	Terry