RE: Metal Screws and Salt Water Caps

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

Original poster: "Steven Ward by way of Terry Fritz <teslalist-at-qwest-dot-net>" <srward16-at-hotmail-dot-com>

I would have to say that sounds pretty good.  Im not using an RFI filter, 
but i do have a large PFC bank.  The safety gap is tied to mains ground as 
well as the cores.  But the breakdown does not always occure with a safety 
gap firing.  My safety gap does not fire all that often with the vacuum 
type gap.  It only fires if the arcs hit some part of the primary circuit 
that the strike rail cannot stop.  So from what Sean and Gary are telling 
me, what could possibly be a solution?  Would an RC filter help?  OR do i 
need better grounding?  I will go and add more insulation to the NST core 
(note that only 1 transformer has the problem, and it always arcs at the 
same spot).  I just added a layer of electrical tape , and it seems to have 
broken through it, so i need something better.  It just occured to me WHY 
only one has this problem!  When i rebuilt the NSTs, i put one of the 
primaries the wrong way, so i had to wire the primary coils opposite, to 
get correct phasing.  That means that one primary has a neutral at its 
inside windings, and the other is HOT at the inside.  Im guessing that the 
hot is the one breaking down becuase there would be more potential.  Or i 
could still be wrong.  Well, its too cold to run the coil anyway, so it 
will have to wait until spring time.

Steve Ward.






>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: tesla-at-pupman-dot-com
>Subject: RE: Metal Screws and Salt Water Caps
>Date: Sat, 11 Jan 2003 12:04:19 -0700
>
>Original poster: "Lau, Gary by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><Gary.Lau-at-hp-dot-com>
>
>Hi Sean:
>
>I think you hit the nail on the head.  The primary winding is 169V 
>above/below mains-ground.  But if the NST core is tied to RF ground, 
>depending upon how good that RF ground is, that could be hundreds, maybe 
>thousands of volts above mains-ground.  This is why:
>1) EMI filters are used between the NST and the mains, and
>2) A good RF ground, particularly with higher powered coils, is important.
>
>Is it possible that the RF ground at the Teslathon was less robust than 
>usual, and once that primary-to-core breakdown was made, subsequent repair 
>efforts were largely ineffective?
>
>Gary Lau
>MA, USA
>
> >>Original poster: "Sean Taylor by way of Terry Fritz 
> <teslalist-at-qwest-dot-net>" <taylorss-at-rose-hulman.edu>
> >>
> >> IF anyone knows why the primary core or coil is generating enough 
> potential
> >> to form an arc through at least 600v of insulation, please let me know!  I
> >> do not have any protection but a safety gap.  Maybe i need an RC type
> >> filter?
> >>
> >> Steve Ward.
>
> >Hi Steve,
> >
> >I don't KNOW :-) but I'll venture a guess . . .
> >
> >You're primary of the NST is at ground level (well, or at +/-169 V max from
> >the AC line voltage).  Depending on what you have grounded where, you're
> >coil MAY be pulling the ground potential far away from that.  If the core of
> >the NST is ground to AC line ground, ie earth ground, then you may be
> >dumping considerable power into that ground, pulling its potential up
> >relatively high, wrt the AC hot/neutral, and blowing through the insulation.
> >Also, if this is true, you may have your safety gap tied to the earth
> >ground.  If so, every time the safety fires, your sinking a lot of energy
> >into that ground, probably pulling the potential quite high (of that
> >ground), again, blowing the insulation between the primary and core.
> >
> >If the core is tied to RF ground, then that maybe be floating above/below
> >the earth ground, and AC reference, causing a large differential, and
> >blowing the insulation.
> >
> >I hope that actually made sense :-)  Any one else have any ideas about what
> >I said? or do my thoughts only make sense to me?
> >
> >Sean Taylor


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