Re: SRSG motor - HELP!!!!!

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Greg,

Normally sync motors run forever in this relatively light duty.  I don't
remember ever hearing of one failing.  Here are the possibilities I can
think of.

1.	The motor was defective or damaged during the sync conversion.  If the
windings were shorting and arcing, that could do a lot of damage.  If there
was metal dust or "chunks" of metal from the conversion grinding around in
there that could cause problems too.  If the starter switch in the motor
failed, the starter winding and start cap would blow up pretty quickly.

2.	The flats were too big and the motor overheated.  But it would smell and
smoke long before it actually blew up.  Perhaps the motor was barely
designed for intermittent duty to begin with.  Unequal flats could cause
poor starting and maybe even some odd voltage and/or current spikes.  In
this case, the windings would show signs of prolonged heat damage too. Try
to make them even next time ;-)

3.	Is it possible that the primary current jumped the insulation and
grounded to the motor shaft?  Normally that current would go through the
bearings into the grounded motor case.  But if the case was not grounded,
it would arc into the AC wiring causing some pretty wild damage.  Check the
insulating disk really well and ground the motor case well.


Next time...

First, I would check over the blown up motor really well search for clues
as to what may have happened.

Second, check to see if the next grinder motor is for intermittent duty or
of poor quality.  Maybe run it hard first before converting it just to be
sure it is sound.

Convert it carefully.  Here are my notes about converting a motor with an
angle grinder (cheap and easy).

http://hot-streamer-dot-com/TeslaCoils/Misc/sync_motor.txt

Be sure the motor case is grounded and the insulating disk is sound and not
arcing over to the shaft.  Also if it has a centrifugal switch, be sure it
operates correctly.  It should turn off the starter winding after the motor
reaches about 500 RPM.  The starter windings and starter capacitor normally
only run about 1 second during startup.  If they stay engaged, something
will blow up but it is usually the starter cap.

I would think the above would almost guarantee the motor will not fail
again.  There just isn't that much to go wrong so I would guess something
was very wrong the first time.

Cheers,

	Terry




At 01:33 AM 6/10/2002 +1000, you wrote:
>Hello all,
>
>Today I was running my coil and getting solid 8 foot arcs, when
>suddenly, and rather destructively, the SRSG motor died. The motor is a
>1HP bench grinder, which I had modified to run in sync. I think it is a
>capacitor run motor. Upon inspection, some of the windings were melted,
>and the entire motor was full of carbon. I saw no reason for it to fail.
>No sparks hit it while operating. It all happened rather suddenly. I
>have had some funny problems with this motor. Often, when applying
>power, it would just sit there and vibrate back and forth, as if it
>didn't know which way to spin. Could this just be because I stuffed up
>when grinding the flats (off centre, unequal size, etc)? Could this and
>the failure be related (was the motor drawing excess current, causing
>the wires to melt etc)? Before I go and buy a new grinder, are these
>motors suitable for this pupose, or are they doomed to fail?. It was
>definitely running in sync ok. Has anyone else successfully used one of
>these motors for sync operation?
>
>Cheers,
>
>Greg Peters
>Department of Earth Sciences,
>University of Queensland, Australia
>Phone: 0402 841 677
>http://www.geocities-dot-com/gregjpeters
>
>
>