[GreenKeys] Starting Up an Old Debate

[WA5CAB at cs.com]

Bob,

I don't know too much about M28's or the later rubber band and door spring 
machines but if you are talking about M14/15/19 sets, I think you are confusing 
pulling magnet selectors and holding magnet selectors.  Pulling magnet 
selectors work on 60MA only.  It was only the holding magnet selectors that were 
switchable 20/60.  The big round pulling magnet selector solenoids are already 
wired in series to operate at 60MA.  The smaller almost square holding magnet 
solenoids take less power to operate because they don't operate across an air gap 
like the pulling magnet ones do.

Also, I vaguely recall a post earlier today that mentioned operating selector 
magnets in saturation.  You don't normally operate iron core electromagnets 
or transformers with their ferromagnetic component driven to or past saturation 
(saturable reactors, mag amps, CV transformers, etc. are special cases - lets 
not go there).  The reason for using the iron core in the first place is to 
reduce the NI (ampere-turns) required to do whatever it is you are trying to do 
(and to help confine the mag field to a smaller volume).  When you saturate 
the core, its mu goes to 1 (the relative permeability of air) and crudely put 
it "quits helping".

In a message dated 5/30/2004 9:13:36 PM Central Daylight Time, 
letourneau at wiktel.com writes: 
> >The question is: since we don't work for the phone company .... why not
>   >use a 40 ma parallel loop? It should work just fine. It would use a
>   >lower power power supply than a 60 ma loop. Think of all the energy we
>   >could save :) ...  It would be something new to try with 70 year old
>   >machines ....

Robert Downs - Houston
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