Andy Dingley wrote:

On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
wrote:

In the 'old' days; mains powered clocks (squirrel cage, synchronous)
were common.

This is Usenet isn't it? There'll be complaints....

Of course not all clock motors are shaded pole. The Warren Model A
was, back in 1916 (I think the first synchronous clock motor)

However the well-known Westclox / Sangamo design of the '30s and
onwards
used an induction rotor - effectively a "squirrel cage". This gave
good starting torque, but obviously had the slip problem. To keep it
locked and synchronous there was also a permanent magnet rotor. This
gave adequate torque at synchronous speed, without slip, but wouldn't
have been able to start the clock unaided.

Some British designs used a single permanent magnet rotor and required
a mechanical pushbutton, or an extra winding for starting.

I have an old Smith Sectric electric clock that was, I think, new in
1942. It maintains time accurately as compared with a radio clock, so
long as the power doesn't fail. When I was very young I remember being
the only person in the house who could get it going again after a power
cut. One was supposed to set the time and jab in the setting knob to
start it, but that seldom worked. At about the age of five I discovered
the best way was to remove the motor cover and spin the wheels inside.

Edgar