[GreenKeys] Why Dual Coil Electromagnets?

[Brooke Clarke]

Hi:

I seems that for most of the 1800s in telegraphy, stock tickers, district 
alarms, and clocks (probably in more places that I haven't looked at yet) the 
electromagnet is formed by placing two coils side by side and connected in 
series with the fields aiding.

Do the early Teletype machines use dual coil electromagnets?

It seems that more modern electromagnets are single coil.
Are there any patents that point to why it was done with two coils then?
Maybe it relates to efficiency?  For example I have a Self Winding "Western 
Union" clock that uses a pair of coils for the self winding vibratory motor and 
another bigger pair of coils for the hourly synchronizing electromagnet.  The 
winding motor runs from 3 volts (two 1.5 volt batteries).  It sounds like a 
small air compressor that might be driven by a fractional horsepower motor, yet 
the batteries are supposed to last a year.  I'll know in a year, but for now 
think it must be a very efficient motor.

http://www.prc68.com/I/SWCC.shtml
-- 
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com