RE: Neon unpotting dilemma (high power factor)

To: tesla-at-pupman-dot-com
Subject: RE: Neon unpotting dilemma (high power factor)
From: "Lau, Gary" <Gary.Lau-at-compaq-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Tue, 07 Mar 2000 11:50:34 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

I would guess that your diagnosis - the PFC cap shorting out for some
reason, is dead-on.  The proof will be when you power it up, minus the bad
cap.

Too bad they don't insulate these things better to support running at the
rated (open-circuit) secondary voltage.

Regards, Gary Lau
Waltham, MA USA


>Original Poster: "Adam" <adamsmith-at-mediaone-dot-net> 
>
>I have just finished soaking my unpotted France 12/60 H.P.F. parts in
>gasoline for a week.  I've got all the parts cleaned off enough to tell
what
>they are, and now I have a bit of a complicated post mortem situation.
>
>The unit failed when I fed it 140 instead of 120VAC. For 10 minutes or so,
>it was not giving any output.  Then, when it cooled off, it resumed high
>voltage output, but now it was humming loudly and pulling 25+ amps from the
>mains instead of the 4 to 5 amps it should take.  It also got really hot,
>really fast.  My initial diagnosis: shorted primary coil.
>
>BUT... when I opened the unit, I see that the situation is a bit more
>complex.  The primary seems to be tapped, with a PFC capacitor across only
>part of the coil.  Could a failed PFC cap have been the actual cause of the
>primary short? I'm thinking now that the HV may have arc'd to the PFC cap
>(which was near the HV wires) and killed it, effectively shorting the
>portion of the primary in parallel with this capacitor.
>
>Unfortunately, cooking the NST on a hotplate totally killed the PFC cap ,
it
>bulged and leaked.  So I'll never know if this cap had really failed, but
>the primary coil seems intact.
>
>Any thoughts?
>
>-Adam
>adamsmith-at-mediaone-dot-net