OT Re: Is this true?? (TI & watches)

Tony Duell ard at p850ug1.demon.co.uk
Wed Feb 21 18:27:51 CST 2007


> > 
> > 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



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