Re: NST filter failure?

["Mark Broker" <broker-at-uwplatt.edu> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Terry,

These messages continue to show up in the middle of the "Avalon lockout safety
thread"....  I guess I'll just have to move that thread to my Avalon
archives.  :-)



> I ran models today of this and shockingly they do not predict fuses
> blowing.  I think this odd saturation thing is at work here because that is
> one thing the models do not predict.  I "think" I have all the other bases
> covered...  Apparently, there are conditions where NSTs will draw huge
> amounts of current.  I know form the noise and the lights dimming that what
> ever is the cause, it is "bad"!

I was told that the lights in the building dimmed slightly even when it was
firing
well.  I believe Walker said the lights dimmed more when it wasn't working
well.


> I wonder if the motor is fine but the current draw from the coil is so
> great that it is affecting the AC power and that is causing the motor to
> loose sync.  Check the motor very carefully before saying it is bad.
> They're is very little that can go wrong with a motor.  Maybe the coils and
> the motor are "talking" to each other on the input AC and it is more a
> matter of getting a lower impedance AC line to them both.  Were you using a
> long extension cord or any other higher resistance feed line to the coil
> and the motor?  If the motor is fine except when the coil is running, the
> AC line input to the motor must be seeing some major disturbance.

>
> The motor could simply have a loose connection in it somewhere which is
> opening when it gets hot.  It should be easy to find any such problems in
> the motor if you open it and have a look around.

Yes, we were using Chris's kludged extension cord, which was about 50 feet or
longer for JUST the motor.  But, it appears that the NSTs and the motor were
running on the same circuit, which they weren't really designed to do
(unless it's
a 20A line).  Chris and I ran the "standard" setup that "failed" (minus one PFC
cap) on his door step with both the motor and NST running off the same
power cord
(standard 10A "garden grade" orange extension cord), but we were running
off a 20A
fuse, with a short length (maybe 20 feet) of 12 AWG Romex between the
outlet and
the breaker box.

When "testing" at school before summer, I was running everything off of a
single
(assuming 20A) line that emerged from the ground in the middle of the
courtyard at
school (probably same length of wire between the TC and the circuit box).

The motor will stay synced down to about  80V.  We were loosing sync at the
demo
despite overvolting the motor (~140V).  I cannot imagine that the "house
wiring"
caused that much of a voltage drop.

I'll look at the connections.  They could have wiggled loose, despite the metal
junction-box clamp (I forget the technical term), which could have caused just
enough added resistance....  The case of the motor was perfectly cool, but
I didn't
check the wires.....

I also think that my RFI filters are backwards.  I have them line-to-line,
load-to-load, and I think that's backwards.  I really didn't think that it made
much difference, tho, judging by a quick inspection of the circuit
diagrams.  I'd
like to place them after the variacs, anyways (getting small shocks from both
variacs ever since I first got it running well).


Since it's being stored at my apartment (house that I rent) at school, I
may set it
up there, and "play," as I'm moving in a week early, and will have a bit of
spare
time before classes start....  Scare the stuffing out of my neighbors, and my
landlord (who is a neighbor)  >:-)

Thanks for the info, Terry.  Will keep everyone posted.

Mark