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Re: First Light at Last! (update)



Gary, Bert, and others,

Just as a clarification, and another question.

I have a safety gap across my RSG (re-designed: see "NST saturation post").
 The
RSG was set to "just about right" when it happened.  The motor is at least 4"
from any NST terminal, and there  is no way possible that the arc from the gap
jumped to the motor (I *REALLY* wish that I had a web page so that you
could see
it).

I am running the motor on a variac (not the NST variac), which I only use to
start the motor.  I set it to 120 after the motor spins up.  My "control panel"
is set up such that the NST and motor can be run from totally seperate "house"
circuits, since I was thinking that I'd end up drawing about 22A total....

If the motor failed at it's weakest link, then why didn't a insulation on the
turns fry?  Or, why didn't it arc across the connection terminals, which are
only about .5" apart in air?  (The arc from the thermostat was about .25"
through some tough, thermoset plastic.)   I certainly hope that I don't further
mess the motor up when I add another NST (with a corresponding increase in the
LTR cap).

Thanks!

Mark

Tesla List wrote:

> Original Poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com>
>
> It sounds like you had your sync motor on the same variac as your NST?  You
> probably shouldn't.  First, the current draw of the motor increases
> considerably with increasing voltage.  Additionally, it had been mentioned
> on this List that the phase of a sync motor may be varied by running it
> through a variac.  Perhaps the phase was such that the cap voltage was near
> a minimum at gap presentation time and not fire, and this allows the cap
> voltage to ring up on subsequent cycles to hazardous levels, perhaps enough
> to arc to the motor?  This would be consistent with the arcing through the
> plastic bottom.  You should have a safety static gap across your RSG to
> protect against just such a scenario.
>
> Regards, Gary Lau
> Waltham, MA USA
>
> >Original Poster: "Mark Broker" <broker-at-uwplatt.edu>
> >
> >Hello, all,. just an update
> >
> ><snip>
> >
> >> Then, the motor
> >> blew while I was turning up the voltage on the NST bank (happened around
> >> 130V on the NST variac).  Disection will ocurr tomorrow and Wednesday.
> >
> ><snip>
> >
> >It turns out that the motor's thermostat blew.  It was packaged in a
> thermoset
> >plastic case that was press-fitted against the outer can and the winding
> >block.  There was heavy weld marks on the quick-connect terminals and the
> >termostat terminals inside the plastic case.  What is curious is that the
> thing
> >arced THRU the bottom of the plastic box to the winding block....  What is
> even
> >more curious is that the motor was room temperature when this happened
> (total
> >run time to this point was less than 5 minutes spread across 5 or 6 runs).
> I
> >replace the thermostat with a piece of wire as a fix (motor shouldn't get
> hot
> >enough to make a difference)
> >
> >So, the question still remains, what on earth happened to this thing?   The
> >motor was old, but I know for a fact that the thermostat was fine when I
> >modified it for sync operation.  The only explanation I have is that
> somehow
> >the "weird and unusual" electric and magnetic fields present beneath the TC
> >(mounted just below the primary) somehow affected it.
> >
> >Mark