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Re: Variac arcing = kickback? (fwd)
---------- Forwarded message ----------
Date: Thu, 15 Jan 1998 15:16:29 -0700
From: Bill Lemieux <gomez-at-netherworld-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Variac arcing = kickback? (fwd)
Adam wrote:
> absorb the impact before it hits the line filters. Then finally, a MOV
> across the mains input to the whole setup.
Keep these factoids in mind about MOV's:
1. MOV's are sacrificial components with a finite amount of energy they
can absorb
over their lifetime. Every time they take a surge, the "use up" some of
their
life. The bigger the hit, the more the unit's life is shortened. I am
not making this up- ask an MOV manufacturer.
2. When MOV's finally fail, they _never_ do it politely. In the case of
so -called "surge arrestors" (more are actually shunt-mode surge
divertors), this almost always results in the unit catching fire. More
than few houses have been burned to the ground as a result of surge
arrestors catching fire, and as a direct result, federal regulations and
more stringent UL testing requirements are being developed.
3. MOV's _do_not_play_well_ in a high-energy noise (ie, HV RF)
environment- they fail very early.
4. When an MOV in a surge arrestor turns on, it diverts current to the
ground- this can be bad if you happen to have equipment around that
needs a quiet ground plane (think LAN's). Not usually a problem for
most coilers, since most of us have the sense to unplug our sensitive
electronics when we're operating a TC within 100 yards of any
electronics we own. :-)
It is for the above reasons that I have replaced the shunt-mode surge
arrestor on my computer system with a Brick Wall from Price Wheeler-
currently the only manufacturer I know of who make a no-MOV surge and
noise _blocking_ unit, ie, a series-mode surge arrestor. I still have a
Tripp-Lite unit on my stereo equipment, but that is slated to be
replaced by another Brick Wall when $ permits.
Fortunately, I have somewhere else to do my TC development work, miles
away from my home. :-)
> Another question: Should the line filter's ground go to the RF ground?
Yes. The RF inductor portion will block some RF, but it is the job of
the capacitor section to conduct any remaining RF to
"somewhere-else-not-the-power-line" via ground.
> And what about my second safety gap- would this also benefit from a
> grounded center terminal?
Urm, tell me again where that second gap is in your circuit topology?
-Gomez
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