Re: How to modify a motor for sync, was Design Problem

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Kidd6488-at-aol-dot-com>

Hi John, CJ, all 

I was thinking about the syncmot.zip file on hot-streamer and how it said 
don't make the flat to shallow, or too deep. I think I have a way to find 
perfect depth. Find the length of the dead-pole and trace it on to the rotor 
so it looks like two parallel lines. Then, instead of filing length wise, 
paralell to the rotor, file it perpendicular, until the flat is wide enough. 
then you should have exactly enough left. Unless I'm wrong, the flats should 
be that: "flat" right? Not like a canyon, with "walls". You guys know what I 
mean right?!?! 

Jonathon Reinhart 


In a message dated 7/8/01 01:16:00 PM Eastern Daylight Time, tesla-at-pupman-dot-com 
writes: 


>
> CJ, 
>
> You can easily modify your motor with a large simple hand file, to 
> make it synchronous. 
> For your motor, you need to file 4 flats equally spaced around 
> the squirrel cage rotor in the motor.  Open the motor, remove the 
> shaft with the rotor, and carefully measure the rotor diameter. 
> It's probably about 3.3" diameter.  Make each flat about 1/4 or 
> 1/3 the total diameter.  For a 3.3" dia rotor, you could make 
> the flats 3/4" or 7/8" wide for instance.  Wider flats will make 
> the motor run hotter and draw more current, so there's no 
> point in making the flats wider than needed.   There is a dead 
> pole concept for modifying these motors, but many small 
> motors don't have dead poles, so the concept should be ignored 
> in those cases.  I don't think it helps anyway.  Measure 
> carefully so the 4 flats are all teh same width and and equally 
> spaced around the rotor.  You can put the rotor into a vise to 
> hold it while you're measuring and filing it.   
>
> After the motor is modified, you can test it by observing a line 
> drawn onto a sheet of cardboard and taped to the shaft.  Use 
> fluorescent light to observe the line.  The line will form an 
> unmoving pattern when the motor is locked.  Raise the voltage 
> gradually via a variac, and you'll first see the pattern spinning, 
> then slow, and lock as the voltage is increased.  The sound 
> will change too and become very steady.   Just before locking 
> the motor will make an unsteady hunting sound. 
>
> John Freau