[GreenKeys] Starting Up an Old Debate

[Bob Camp]

Hi,

You are right. The only parts I am talking about are those that will 
run from both 20 ma and from 60 ma. A model 15 printer is a good 
example (or at least all of mine were). Of course we have already 
established (based on my weird model 28's) that judging the world by 
the collection of machines in the basement can be a bit dangerous ...

The saturation thing is still an open question. I have no idea if the 
20 ma magnets saturate at 30 ma per magnet or not. The materials used 
in the core would have to be pretty carefully selected to make it 
happen. If they wanted to Teletype certainly had the horsepower to do 
it . I wouldn't want to bet any major money on saturation though. It's 
certainly a very unusual way to run a core.

I'm not sure that saturation would keep the selector from working 
though. As you run a coil up into saturation you stop getting more 
energy storage as the current increases. Last time I looked it seemed 
like you still kept the energy you had already put in. More or less the 
magnetic field stops getting bigger but it does not get any smaller. 
Magnetic core memory on computers worked that way. Haven't seen many 
core boards recently ..... The great debate over ferrite versus 
powdered iron in switching power supplies runs in circles around the 
details of saturation effects in inductors. Saturation is not an 
absolute state often cores are run in a region that is near the maximum 
flux density but not over it. In that region the inductance is dropping 
but has not gone to zero. Needless to say that only makes things more 
complex ( one more state to worry about ...).

	Take Care!

		Bob Camp
		KB8TQ



On May 30, 2004, at 11:53 PM, WA5CAB at cs.com wrote:

> 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
> <http://www.wa5cab.com> (Web Store)
> <wa5cab at cs.com> (Primary email)
> <wa5cab at houston.rr.com> (Backup email)
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