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

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

 

 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 --

And lots fewer turns on the primary.

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

I'd not actually think so.
As I've said before I'd salvaged a torroid from an expired
high powered car stereo, 300 watts, and it was quite close to the size
of the torroids in computer power supplies I've seen.
It may have been the _exact_ same size as it looked to be so but
I never actually measured it.

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

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

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

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

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

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...  :-)

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

 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.

 Yes you're right about the gap.
 As I say from that salvaged torroid there was plenty of room for
 the high current winding.

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


 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.

My smallest is 150 out of a P.B.

 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,

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

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

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

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

 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.  :-)   

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