WAYNE CHIRNSIDE wrote in a message to ROY J. TELLASON:

-=> ROY J. TELLASON wrote to WAYNE CHIRNSIDE <=-

 RJT> WAYNE CHIRNSIDE wrote in a message to ROY J. TELLASON:

 WC>  

 WC>  You might need to adjust the torroid core parameters

 RJT> I wouldn't even begin to know where to start with that one.

 WC> Actually thinking it through again I cannot see this being a
 WC> problem at all.  Why would a core care if the amps were on one
 WC> side, the other or both?  As it stand those cores carry a LOT of
 WC> amperes on the secondary.

 RJT> Yep,  and lots of amps means heavier wire --

 WC> And lots fewer turns on the primary.

True.

 RJT> where are you gonna put it?  I'd bet that there isn't room for it 
 RJT> in existing cores,  so you're talking about rebuilding the 
 RJT> transformer into something a bit bigger than what you started 
 RJT> with.

 WC> I'd not actually think so.

It'd be my guess,  but...

 WC> As I've said before I'd salvaged a torroid from an expired high 
 WC> powered car stereo, 300 watts, and it was quite close to the size 
 WC> of the torroids in computer power supplies I've seen.

That's the other thing -- I've only ever seen toroids in computer power
supplies used as a part of the output filtering,  never as the transformer
that's in the middle of things.  Which may or may not mean a whole lot, 
since there's a lot of ways to build stuff and I'm no way claiming that
I've encountered even a significant chunk of it.  I can only go by what
I've seen, though.

There happen to be two dead ATX supplies here,  and I just looked in both
of them.  Both have regular E&I lamination transformers in there, 
roughly the same size.  I don't remember ever encountering anything else in
there.  Even the ones that used a transformer for regulatory feedback used
one of those too,  although it was a smaller one.

 WC> It may have been the _exact_ same size as it looked to be so but I
 WC> never actually measured it.

 WC> Anyway that transformer _was_ carrying similar amperage as 
 WC> required and the wire fit nicely with even a bit of room for 
 WC> another winding.

Ok.

 WC> I'm still annoyed that I tossed it when last I moved :-(

It's like that tagline:

"Junk = stuff we throw away, Stuff = junk we keep",  or something
pretty close to that...

 WC> Still I've a spare 150 watt AT supply I could play with.

I'm planning,  once I get things a little better straightened out in here, 
to go get myself a bunch of junk power supplies to see what can be done
with them.  If nothing else I can at least use the boxes for some projects,
 and get some useful parts out of them.

 RJT> Not something I'd care to tackle,  but then I never did get along 
 RJT> all that well with inductors...

 WC>  One day I needed a 24 volt center tapped transformer but was 
 WC> stone cold broke, separated the laminations, unwound the wire, 
 WC> rewound half, tapped it and finished up with a coat of shellac. 
 WC> Took a bit of time.

I guess it would!  :-)  Lucky for you the secondary winding was on the outside...

 WC> Snip.

 RJT> I actually did stumble across one site (Russian?) where they provided a
 RJT> schematic of an ATX power supply and an explanation of how it worked.
 RJT> I can email it to you if you like.  Unfortunately it doesn't match what
 RJT> I have on hand here to try and figure out...  :-)

 WC> Don't bother, I can search for same if I care to.

Ok.

 WC> I merely was referencing a project I did when I very successfull 
 WC> employed a color T.V. flyback transformer where I applied an 
 WC> external winding, powered it from a stiff 12 volt supply with
 WC> spectacularly successful results.

 RJT> Yeah,  but on those you have a lot more core to work with -- and those
 RJT> cores have a gap built into them so they won't saturate,  I don't know
 RJT> if that's the case with switching power supply inductors or not.

 WC> Yes you're right about the gap.

I don't know why,  but the repair.faq documents I was reading seemed to
feel it necessary to mention that a bunch.  I think in one place of several
that they mentioned it they said something about taking the core apart, 
but the last time I did that with a flyback was with some 1960s vintage
stuff.

 WC>  As I say from that salvaged torroid there was plenty of room for 
 WC> the high current winding.

Ok.

 WC>  As to saturation I don't think it would be a problem at the same 
 WC> power levels at the high frequencies used.

I just don't know.  That's a part of it -- I don't know all that much about
doing stuff with inductors.  About the only ones I have anything to do with
at all are the small transformers I use for power supplies,  and that's
it...

 RJT> What wattage were the units you saw?

 WC> I believe around 85 watts which is way to light.

 RJT> Yep.

 RJT> Smallest PS I have here is one I took out of an old P-B that was
 RJT> getting tossed,  it's marked at 100W max output.

 WC> My smallest is 150 out of a P.B.

Probably around the same size box,  I bet.

 WC> Seems manufacturers can make such supplies for those huge wattage
 WC> car stereo amplifiers and they are pretty darn cheap.

 RJT> Sure,  but those are only designed to put out _one_ voltage,

 WC> Two, one I salvaged was center tapped for + and - 48 volts, had
 WC> extra room. add to this the 12 volt windings need not carry heavy
 WC> amps...

Good point.  If you're gonna go there at all,  then this wouldn't be too
much trouble.

 RJT> and there's no telling what the other specs are,  in terms of how 
 RJT> tight the regulation needs to be,  etc. -- probably not very.

 WC> I'd think once you were in the ballpark the controlling duty cycle
 WC> switching power supply wouuld take care of the regulation nicely.

Yeah,  probably,  with some feedback.

 RJT> While there's *some* comparison I don't think they're exactly 
 RJT> what you could call parallel.

 WC> That's where the duty cycle switching control chip enters the 
 WC> picture. IIRC it's regulated to the 5 volt output with the other
 WC> rails regulation being tied to that. I STILL say it should be 
 WC> quite simple.

 RJT> Ok.

I did get a data sheet on that 494 (?) chip,  which in and of itself wasn't
all that helpful,  but I also snagged some app notes and if I can find
those and the time to review them it might help.

 WC> Have not done it but have done similar as above.

 RJT> Well,  if you go ahead and build one I'll sure be interested in hearing
 RJT> about how well it works.  :-)   

 WC> I'd _like_ to attempt it, 6 - 7 years ago I would have attempted it
 WC> but unfortunately I don't see it happening these days when my last
 WC> reserves are expended just trying to maintain independence and keep
 WC> a reasonably clean apartment.

Well,  maybe after I get to messing with some of those power supplies I'm
supposed to get a hold of I'll have a somewhat different perspective on
this stuff,  we'll see.

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