Re: better sync motor mods & questions

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

Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>" <FutureT-at-poodle.pupman-dot-com>

In a message dated 1/11/01 7:15:35 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes:

> I seem to have observed that the motors here in europa tend to have long
>  rotors of small diametre, compared to american types?

Finn, all,

I notice that motors that have no run or start cap, tend to be
often large and bulky.  Motors with a run cap tend to be smaller
in overall diameter.  The addition of the run cap makes the motor 
more efficient, compared to the split-phase method centrifugal
switch start-winding type.  I don't know why the europeans use
a long slender rotor.  I would expect to see that in a high speed
motor.  

>  
>  Anyway, the kind of motor makes a difference too:
>  I have just, for the first time, modified a motor with a start cap and
>  centrifugal switch. 0.25kW -at- 1500 rpm. Without further considerations i
>  started out with 4 flats, 1/3 as wide as the rotor diametre. 

1/3 the diameter does not seem very narrow though.  I'm beginning
to think that 1/4 the diameter is better for at least some 4-pole 
motors? 

>  Result: A
>  motor that locks in at a modest 95 volts, and doesn`t loose it before
>  the voltage drops to 65 volts, driving the same 11 inch rotor. Starts to
>  sound bad from 200 volts, and up, although the current is not exeeding
>  the (RAT)ed 2,1 amp.
>  So it seems that motors with start cap need smaller flats, compared to
>  motors with only the run cap.

Here's a speculation:  Maybe a small flat is best when the motor is
locked already (lots of torque).  But a wider flat helps the starting?
So a cap-start motor has more start-torque anyway... so it can tolerate
the smaller flat for starting, and gains an advantage while running?

By the way, do at least some of those motors have any dead poles,
with field slots with no wires though them?  Maybe motors with dead
poles, can tolerate or require wider flats?

I will not be doing any more of these tests, but I look forward to the
results from others of such comparison tests of flats, V cuts, etc.

My questions:
1.  Is a V cut any better than a flat cut?  How much better?
2.  Does a V cut need to be narrower than a flat cut?
3.  How critical is the shape, depth, etc of a V cut?
4.  Does the best width of the flat depend on the motor loading?
5.  How much does the needed proportional width of cut vary for
     different types and/or sizes, and why?
6.  Do motors with dead poles need wider cuts?
7.  Do 3600 rpm motors need wider cuts than 1800 rpm motors?

John Freau 

>  
>  I have 3 more of these motors
>  250W -at- 3000 RPM
>  370W -at- 1500 and 3000 RPM, and I will take more care when I modify these.
>  
>  Cheers, Finn Hammer
>