21 Feb
2007
21 Feb
'07
4:27 p.m.
>
> Does anyone remember that the oldest of said wall clocks required the
> owner to start the motor manually by spinning a little knurled shaft
> located on the back?
I've enver actually used one, but I've seen them, and read about them.
Another method that was common over here was to have a spring-loaded
lever that was operarted when you pusehd or pulled the set-hands knob to
set the time. Releasing said knob caused the lever to give a 'kick' to
the motor's rotor to get it going in the right direction. These little
synchonous motors were symmetircal and could run either way, so you might
end up with a clock that runs backwards :-).
Mroe recent clocks have a mechanism that detects if the motor is turning
backwards and if so, stop it and kick it back again, thus getting it
going the right way. On a clock fitted with a second hand, you will see
it run backwards for a few seconds sometimes when you connect it to the
mains until said device operates and getis going the right way.
I seem to recall a rumor where the power companies were offering to replace at
no charge those clocks that needed to be mamually started (before my time.) The
reason had something to do with using power that didn't register on the power
meter. Anyone here know if this is fact or fiction?
Soundsl ike fiction to me. Electricity meters, at least in the UK have
(by law) to record true power only. Now, 'reactive power' (an oxymoron
IMHO) is disliked buy the power companies because they don't get paid for
it, but the extra current does contribute to I^2R losses in the power
cables, it does mean heavier cables are needed, and so on.
But, I can't see whay yhr power factor of a self-starting clock would be
necessarily any different to that of an older clock. In any case, the
total current trhugh such a clock motor is tiny anyway, for a normal
house with a few such clocks it is not going to cause any problems.
-tony