Two small complications:
* It must be 2500rpm nominal (it's to replace a 1250rpm motor)
* The shaft needs to be 0.25in diameter (not 6mm) and about 2in long.
These used to be bog-standard items, but they all went to hide when they
saw me looking.
AIUI there is no way to modify the existing 1250rpm motor, because the
speed is determined by the number of 'poles' in the rotor construction.
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
as I said, the rotational speed is a function of the applied voltage,
you totally misunderstand what is meant by shaded pole
I have approaching a thousand, but with 6mm shafts
>Total bollocks - 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
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.
Evenm the non-synchronous ones are pretty insensitive to increased
voltage, as they're limited by the magnetic saturation of the core.
> * It must be 2500rpm nominal (it's to replace a 1250rpm motor)
> * The shaft needs to be 0.25in diameter (not 6mm) and about 2in
2-pole shaded pole motors are readily available,
but only with a 6mm shaft these days.
To get a 0.25" shaft might mean looking in old electrical
> AIUI there is no way to modify the existing 1250rpm motor,
> because the speed is determined by the number of 'poles' in the
> rotor construction.
Many (many) years ago there was a way of getting a 2:1
speed switch with 4-pole motors which had a coil on
For 1500 rpm (off load) the coils were energised in a
N-S-N-S 4-pole configuration and for 3000 rpm (off load)
the coils were switched to a N+N-S+S configuration, to
get an effective 2-pole motor.
Any chance with your present motor?
Notice the 'off load' distinction. These shaded pole
motors do run with a large slip on load, and your
'1250 rpm' 4-pole motor is really a theoretical 1500 rpm
sync speed motor running at 17% slip.
> 2-pole shaded pole motors are readily available,
> but only with a 6mm shaft these days.
> To get a 0.25" shaft might mean looking in old electrical
Router collet shim from a cheap router 8-)
Along with grinding the 6mm cutters into trammel points or doorstops,
it also helps to reduce the risk of ever using one of these dangerous
6mm cutters in your 1.4" collet.
If you can only get 6mm then a couple of layers of ali from a coke can
might shim it out OK.
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
>Please can anyone help me find one of these? It looks similar to
>http://tinyurl.com/3xykj3 but maybe with a deeper stack of stator
I've got a box full of unused 30 year old ones made by ECM Motors of
Schaumburgh with 0.25" shafts, however, all have reduction gearboxes
giving 200RPM at the end. Perhaps you could transpose the rotor from
yours and build one out of the bits you have plus one of them? What
are the dimensions of the one you have?
Or drift the shaft out and replace it with a bit of silver steel
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).
If you're near Watford, I could prolly do it for you (we're just down
the road from Peter)