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RE: NST phasing questions
Original poster: "Lau, Gary by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Gary.Lau-at-compaq-dot-com>
Original poster: "Bill Vanyo by way of Terry Fritz <twftesla-at-qwest-dot-net>"
>I don't know about voltage diffs, but I did get a 15/30 and 15/60
>properly. One odd thing though was that I couldn't get them to phase
>I hooked the primaries in series (as has been suggested on somebodies
>Tesla coil page) - *neither* side of either secondary was nearly in
>phase with *either* side of the other secondary. But with primaries in
>parallel, it worked fine.
Running two 120V NST's on 240V with primaries wired in series will only
work (i.e. the 240V will divide equally between the two)if the two NSTs
are identical. In your case, they were not, and one was getting much
more than 120V, and the other much less than 120V.
>I'd like to see this one answered definitively. I'm using line
>but not backwards, as a recent discussion here suggested that the
>purpose of a line filter *IS* to protect the line, and not the
>equipment, though to me that doesn't seem logical (one faulty device
>pollutes the line, and everything else is unprotected). Recent
>discussions also said most EMI filters are symmetrical so that it
>wouldn't matter anyway, but mine (Sprague) are not - and not being such
>a wiz with electronics, I can't figure out from the schematic which
>they are protecting - line or load, or whether the assymetry even
All of the EMI filters that I've come across are asymmetrical, and the
asymmetry matters a great deal. I have a page on my web site that
addresses this confusing issue. See
The backwards or not question depends upon which ground, RF or mains,
you connect to the case of the filter. The best approach is to locate
the filter at the variac with the mains ground tied to both the variac
and filter case, and with the filter wired "backwards" - LOAD terminals
to variac output, and LINE terminals to the cord going to your NST. For
other cases where the filter is at the NST, refer to the web page.
>The more interesting question to me is what to ground where. Take a
>look at everything that needs a ground connection:
>1) Secondary base.
>2) Strike rail, if present.
>3) NST case/secondary midpoint.
>4) NST protection filter and/or safety gap.
>5) Line filter.
>One web site called it a "deadly" mistake to ground the NST case to the
>RF ground. Right now, I have 1 & 2 above hooked to RF ground, and 2, 3
>& 4 hooked to a seperate spike in the ground (2&3 to one spike, 4 to
>another) - just a really big nail (10") in damp earth. Not that I
>recommend that - I'd like to hear what the experts recommend.
This is a complex question and I don't think a perfect solution exists
(though people do it several ways with no apparent problems). I don't
think it's a good idea to have more than one RF ground. You should just
try to make one as good as you can. The basic problem is that no RF
ground is perfect. This leads to there being high voltage spikes on
this "ground" relative to your mains ground, and also relative to your
mains hot & neutral lines. I would recommend items 1 thru 4 all going
to a single good RF ground, and the EMI filter case hooked up according
to where it is located according to my web page.
Regards, Gary Lau