RE: can this motor be made sync?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Colin Dancer" <Colin.Dancer@xxxxxxxxxxxxxxxxxx>

Interesting opinion, but I'm afraid you're wrong.  Period :-)

I can absolutely assure you that grinding flats on the rotor can and
does convert normal induction motors to sync operation.  I've done this
a number of times, as have many other people. The result is easily
verified with a zero-crossing locked strobe (or a gas discharge light).


Slip is not required to magnetize the rotor.  The rotor is mainly soft
iron laminations, with helical slots normally filled with cast aluminium
and joined at the rotor ends  Under normal conditions (as manufactured)
the slip induces significant currents in the aluminium "windings" and
this strongly magnetizes the core.  The strongly magnetized core reacts
against the "rotating" field generated by the two phase shifted windings
in the stator and this drives the rotor.

When you grind the flats, you stop the slip and with it most (if not
all) of the current in the aluminium winding.  However, you still have
the soft iron core and it is now asymmetric.  The poles of the stator
magnetize / attract the extremities of the soft iron rotor in just the
same way that a nail is attracted to a permanent magnet.  The rotating
field in the stator therefore still generates a torque in the rotor, but
it is now exactly synchronized to the rotating field. Imagine putting a
pivot through the middle of a nail, and then pulling it round the pivot
by attracting the end(s) of the nail using a magnet(s).

The downside, and the reason that this isn't how industrial sync motors
work, is that the induced (ferro)magnetism in the core is much weaker
that the induced (electro)magnetism when the rotor is slipping and
current flows in the winding.  As you say, small industrial sync motors
tend to have permanent magnet cores, with larger units having slipring
driven rotor windings.

Colin.

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx]
Sent: 06 October 2005 22:32
To: tesla@xxxxxxxxxx
Subject: Re: can this motor be made sync?

Original poster: "Dan" <DUllfig@xxxxxxxxxxxxx>

What makes an induction motor a-synchronous, is the fact that the
armature is not magnetized. Period. if the armature does not slip with
regards to the rotating magnetic field, there would be no induced
magnetic field in the armature. That is why induction motors run slower
than synchrony. It's not because it has no flats.
Manufacturers would have thought of that already, if it acutally worked.
No amount of flats is going to fix that. I don't know where that idea
came from, i've seen it before on some website. I just chuckled.

The only way would be to somehow magnetize the armature, but since it is
mostly aluminum, I don't see how you would do that.

Dan

----- Original Message -----
From: <mailto:tesla@xxxxxxxxxx>Tesla list
To: <mailto:tesla@xxxxxxxxxx>tesla@xxxxxxxxxx
Sent: Wednesday, October 05, 2005 7:13 PM
Subject: can this motor be made sync?

Original poster: tesla popp
<<mailto:teslas_lab@xxxxxxxxx>teslas_lab@xxxxxxxxx>

ignore the blank message i acedentally i sent...

I have obtained a source of motors for $2 each.  i tried the flats thing
to no effect.  I slowly ground down the armature until the edges nearly
met, but no luck what so ever.  i figured they would be good for a
"terry blake propeller style rotery gap"

my question for you is:  can this type if motor be made synchronous???

here are some pics

<http://www.amasingscience.com/teslacoils/flats>http://www.amasingscienc
e.com/teslacoils/flats
on
motor.jpg

<http://www.amasingscience.com/teslacoils/motor.jpg>http://www.amasingsc
ience.com/teslacoils/motor.jpg