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Re: SRSG motor anomoly

Thank all for your suggestions.  I thought that I'd post an update.

The motor is a 1/3 HP split phase motor (don't recall manufacurer) pulled out
of a furnace.  The GRade LE rotor is 10" (overkill - should have made it 8")
with 4 thoriated tungsten electrodes on an 8" diameter.  I used an aluminum
ring on the backside (motor side) to connect the brass bolts I used to hold the
tungsten.  For the record, I will be running a 15/120 NST system with an MMC
cap.

I took someone's suggestion to machine the flats a little larger.  I milled off
about 5 mils, so the flats are now about .75" wide.  With the electrodes
installed, I can no longer apply sufficient force to the disk with my fingers
to get the 90degree shift.  I can still (with somewhat more effort) get a small
~5 degree shift.

I hooked up a 10A variac to the motor to test the locking voltage.  After
frying the fuse (appeared to have virtually exploded) by flipping the power
switch with the rotor set to 120V.....  After slowly increasing the voltage to
120V to get the motor started, I was able to turn the dial down to about 80V
before the motor started to make "weird" noises.  The rotor never lost sync
while turning the dial down to 75V (at which point the growling made me a
little nervous).

The good news is that I think that it's "fixed."  The bad news is that it pulls
a significant amount of juice to start it up (takes ~1 second when plugged into
the wall).  I was unable to scrounge up a ammeter that went past 10A and
without a "bananna plug" connection to find the current draw.  My RF filter for
the motor is only rated at 5A, so I hope the steady-state current draw isn't
too much higher than 5A...  Might need to add a PFC cap to the motor :-)

Once again, thanks for the feedback!

Mark B.


Tesla List wrote:

> Original Poster: "Mark Broker" <broker-at-uwplatt.edu>
>
> Hey,
>
> I finished machining 4 flats into the armature of a 1725 RPM 1/4 HP (or
> something close) motor recently.  Today, I attached my G-LE rotor (no
> electrodes yet :-(  )  to the motor and fired it up.  Ran pretty smooth
> after balancing.  I grabbed an old stroboscope and clocked it at 1800RPM!
> I was happy, despite there being no way with this scope to test for rotor
> position vs. the AC cycle.
>
> Then, I applied a little load to the rotor by gently pressing on it with my
> hand.  The rotor position rotated about 10 degrees, then a full 90 degrees
> (to the next pole).  It took surprisingly little pressure to cause this.  I
> was wondering if I need to grind a little more off the armature?  I
> machined 4 flats .675" across, which is the distance between the two "dead"
> poles in the winding.  That is according to the directions I found on
> Terry's site.  Is it possible that the motor is crap?  It was replaced in a
> furnace.
>
> Thanks
>
> Mark B.