[time-nuts] Building a mains frequency monitor
Ron Bean
time at rbean.users.panix.com
Mon Apr 11 15:36:03 UTC 2016
>> A more modern name for a synchronous motor is a permanent magnet stepper
>> motor. Any PM stepper, and a couple of microfarad capacitor becomes a
>> synchronous motor when connected to the power line.
I've seen a data sheet for a motor that's actually spec'd for both uses.
I don't know how common that is.
>The old pre-digital way of generating a rotating field for a synchronous
>motor was a shaded pole. They worked well for low torque applications like
>clock motors. I saw plenty of them when I was a kid. The rotor was hidden
>in a package with the first layer of gears. I assume it was a permanent
>magnet but never took a package apart to verify that.
You're thinking of the Telechron clocks (also branded GE, Revere, and
Herschede). Some good pics of the motors here:
http://telechronclock.com/
https://clockhistory.com/telechron/
Also, lots of pics of the clocks themselves:
http://www.telechron.net/main.htm
There are people who rebuild the rotors, for a fee (usually they'll swap
yours for a rebuilt one). I've fixed one clock this way, and I have a
couple of others that need it.
The other major manufacturer was Sessions, they had a bayonet system
that allowed you to replace the whole motor easily (not including the
gears), but they weren't as durable as the Telechrons.
A friend of mine has an early Sessions clock where the motor is held in
with #5 screws. I'd never seen these before, it took me a while to find
the right wrench to take it apart.
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