Re: Problem with Synchronous Motor and Timing Light

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

Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-qwest-dot-net>" <bigfoo39-at-telocity-dot-com>

Tesla list wrote:

>Original poster: "Daniel McCauley by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>
>
>Okay, so I picked up a strobe light from Radio Shack this evening and with
>Terry's modifications, made me a 60Hz timing light.
>
>I got my SRSG and the timing light, turned the lights off, and tested away.
>
>However, I do not know too much about how synch motors really work, but here
>were my results:
>
>1.  The timing light worked great.  Basically froze the rotor to free time
>so you could see the position of the rotor in respect to the 60Hz input
>power.  However, the problem is that if I briefly touched the side of the
>rotor to slow it down just for an instant (yes, it does burn my finger), the
>rotor locks in speed again, but in a slightly rotated position and will
>continue to move about everytime i slow it down for an instant.  Is this
>normal for a synchronous motor???  I was under the impression that once
>attached securely to the shaft that it would maintain its relative position
>forever unless you rotated the rotor about the motor axel.  What are your
>thoughts??
>
>Thanks
>
>Dan
>
>
>
>
>
>
Hi Dan...

what you are seeing is the effects of "rotor slip". The rotor is made in 
such a way that the core ( rotor)  has rods running the length of the 
rotor, all or the rods are connected to each other via a ring on each 
end. ( kinda like the running wheel used for hamsters). This design 
allows a magnetic field to be created in the rotor when voltage is 
supplied to the field windings.


Anyway...   the fields created by the motors stator ( field windings)  
"lock" onto these rod sets and "push/pull" the rotor around. When you 
slow the rotor (disc) the magnetic field looses its lock on the set of 
rods it originally "grabbed" hold of.  The field will then lock onto the 
next available set of rods in the rotor, thus shifting the grab point 
and giving you the results you are seeing.


Scot D