Re: BIG counterpoise

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

Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-qwest-dot-net>" <mbroker-at-thegeekgroup-dot-org>

12/8/2002 11:20:00 PM, "Tesla list" <tesla-at-pupman-dot-com> wrote:

 >Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>
 >
 >Hi Mark,
 >
 >At 10:17 PM 12/8/2002 -0600, you wrote:
 >>I have a similar grounding issue.  The coil I built and left my physics
 >>department has gone
 >>through 2 transformers, with properly set safety gaps and
 >>TerryFilter.  (Ok, so the ground
 >>wasn't attached to the TerryFilter the last time.)

Upon further thinking, I think that the other failure was due to improperly 
set safety gaps -
the MOVs virtually melted :o  As far as I can remember, I've lost 3 NSTs, 
the first was due
to stupidity - no secondary, no safety gaps, no filter....  The other two 
as described to the
best of my recollection.

The third NST had an unusual failure mechanism that I couldn't really 
identify.  The NST
acted as if the CT had been open circuited, and one LV terminal had been 
shorted near the
end of the winding.  :(  One of the LV ceramic terminal housings was broken 
(worked that
way for quite a while), so I just dumpstered it.


 >I am a little surprised anyway.  The "me" filter :o) should have still
 >provided some protection even without a ground.  You may want to add input
 >fuses if you don't have them already.  I worry about the NST shunts
 >saturating and the NST drawing very high currents.  Since your running it
 >LTR I don't think over voltage should be a problem (the filter should still
 >protect against that anyway).  It could be RF ripping through the
 >ungrounded filter, but I would add a fuse and see if the NST is going
 >nuclear on input current.  This may be really true if the coil's power were
 >turned on without the gap running.  But, the safety gaps should still keep
 >it under control...  I guess I don't see what is hurting the NSTs here...

It seems to me that I'm one of the only reported people to ever go through 
NSTs with your
filter design being used?

I haven't blown a 20A fast-blow fuse in a while.  The last time I measured 
input current was
a long time ago.  I think it was about 15A average, hitting about 17A when 
the voltage was
turned up until the safety gaps fired.  I have 300uF (I think) of PFC 
(15/30 NSTs) installed.
That is approximately in line with the NST PFC spreadsheet I found a long 
time ago on
Terry's site.

The most interesting thing about this latest failure is that no one has 
used it but me since it
was last used (March, 02 until November, 02).  It worked then.  Nothing was 
out of place,
and the safety gaps were still spot on.  But when I fired it, 
nothing.  After about 15 minutes
of head scratching, I decided to check the NSTs.


 >"Flexible" (big spiral) galvanized steel (bad skin effect RF conductor) may
 >not be a great RF ground especially at the higher RF noise
 >frequencies.  But probably "ok".

That's the type, about 1.25" in diameter.  It was removed, tho, when the 
primary lecture
rooms were updated.


 >The concrete floor is filled with rebar and is connected to big iron
 >beams.  It is "sort of" conductive, but a counterpoise (just a little one)
 >to contain the RF stuff should do great here.

Good :)  I suppose connecting it to a water pipe would still be of use?

I'm still contemplating the idea of building a much smaller, more portable 
coil that will fit
better in the new lecture hall.

Thanks for the feedback,

Mark Broker
Chief Engineer, The Geek Group