Re: SRSG motor anomoly

To: tesla-at-pupman-dot-com
Subject: Re: SRSG motor anomoly
From: "Finn Hammer" <f-hammer-at-post5.tele.dk> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Tue, 21 Mar 2000 16:32:07 -0700
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Mark!

I think you are lucky, really, and have not yet taken enough off the
armature.
I have seen this behaviour too.
Try to run the motor up with a variac, with a amprermeter in series. A
analog amp. meter is needed for this.
What you need to observe, is the hunting that takes place before the
motor locks into sync. mode, and the voltage that this happens at.
In your case, the locking probably happens too close to full line
voltage, therefore there is not enough power to hold it in sync mode.

Try to shave, say 4 mills more off each flat (this is thickness, not
width of the flats) then reassemble the motor and try again. You will
see that the motor now locks in at a slightly lower voltage, and draws a
bit more current at sync speed.

The tradeoff now is to stop shaving off material, before the motor draws
too much power at full line voltage, but still is able to pull the rotor
with the electrodes.

Hope this helps!

Cheers, Finn Hammer

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.