In message , Ian White
writes
raden wrote:
In message , Andy Dingley
writes
On Tue, 04 Sep 2007 00:10:34 GMT, raden wrote:

Total ******** - more volts - faster rotation

the shaded pole is the pair of thick copper wires on the laminations,
its there to determine the direction of rotation, it has no effect on
the speed

Shaded poles motors may be synchronous or non-synchronous, depending on
how their rotor is constructed. For the small low-torque models used to
drive timers, they're almost universally synchronous.

You have looked at the photo he linked to, I presume


Evenm the non-synchronous ones are pretty insensitive to increased
voltage, as they're limited by the magnetic saturation of the core.

I should have said "within a range" up to where they approach
saturation ...

Of the boiler fans which run at two speeds (purge and full), most are
voltage controlled - its cheaper than having a second winding

Thanks for all the comments. The source of my confusion about numbers
of poles was that I have two shaded pole motors, one that runs at about
2500rpm (about 80% of synchronous speed) while the other motor runs at
about half the speed. On closer examination it seems that the rotor and
stator construction is actually the same in both motors, and the slower
speed is due to one of the stators operating at lower magnetic flux.

The rotors and stator/winding parts of the 'fast' and 'slow' motors are
mechanically interchangeable, so I tested all four combinations at
230V. One stator/winding could make both rotors run at about 2500rpm,
while the other made them both run at about half that speed.

All four combinations could be slowed down by reducing the voltage, so
it looks like the general case is more magnetic flux = faster rotation.
Or to put it another way, more magnetic flux = less slippage under
load, and a closer approach to synchronous speed.

Thanks also for the suggestions about shimming up a 6mm shaft to
0.25in. One layer of PVC tape worked surprisingly well, as the balance
at 2500rpm was not as critical as I'd expected.

However, the project then hit another snag, as the faster motor is
clearly not designed for continuous operation and gets uncomfortably
hot after about half an hour. I will grateful to take up Peter Parry's
offer, and try to find a better motor (will contact you by e-mail
tomorrow with dimensions).

You can buy cooling rotors at some rip off price (several pounds) from
your local HRPC or Partcenter. They are 6mm but you could quite easily
drill one out to 1/4 inch. You just need to push the shaft through far
enough to accept it

If you're near Watford, I could prolly do it for you (we're just down
the road from Peter)


--
geoff