adams@swbatl.sbc.com (Tom Adams - 235-7459) (09/12/90)
In article <15286@shlump.nac.dec.com> sreekanth@rgb.dec.com (Jon Sreekanth) writes: > >By far the cheapest solution is to buy an XT power supply. Prices are >below $50, if you look around, and the beast is going to supply 135 watts >at least. Could someone explain what a PC power supply needs connected in order to function? I've tried to use old PC supplies on the bench and can't seem to get any voltages out. PC repair books (which all seem to recommend trashing switching PS's when they act up) suggest that there are a monitor lines that need special treatment. -- uunet!swbatl!adams or adams@swbatl.sbc.com Tom Adams: 314-235-7459: Southwestern Bell Telephone Advanced Technology Lab BOOKS WANTED: pre-1930 radio, electrical & scientific topics
wolfgang@wsrcc (Wolfgang S. Rupprecht) (09/12/90)
adams@swbatl.sbc.com (Tom Adams - 235-7459) writes: >Could someone explain what a PC power supply needs connected in order to >function? I've tried to use old PC supplies on the bench and can't seem >to get any voltages out. I have just such a gem here. The trick is that on cheap imports, they just assume that the 5v has some moby load on it. The Taiwan clone "200w" KPI supply I have needs a 1 ohm (25w) load on the 5v to work well. Well defined as the 12v supply actually being within 10% of its rated voltaage. ;-( With no load the thing goes into over-voltage trip mode. With a small load of 1/2A, it does power up. It just has poor regulation on all supplies. You see it looks like there is really only one regulator in this whole box. They just assume that all supplies track, and you will naturely want to draw at least 5A at +5v. aaaaaarrrrgggg! Anyone have a brand name for a PC supply that actually *would* put out 12v @ 3A without wasting 25watts at 5v? -wolfgang -- Wolfgang Rupprecht uunet!{nancy,usaos,media!ka3ovk}!wsrcc!wolfgang Snail Mail Address: Box 6524, Alexandria, VA 22306-0524
depolo@eniac.seas.upenn.edu (Jeff DePolo) (09/13/90)
In article <1990Sep12.142550.9853@wsrcc> wolfgang@wsrcc (Wolfgang S. Rupprecht) writes: >adams@swbatl.sbc.com (Tom Adams - 235-7459) writes: >I have just such a gem here. The trick is that on cheap imports, they >just assume that the 5v has some moby load on it. The Taiwan clone >"200w" KPI supply I have needs a 1 ohm (25w) load on the 5v to work >well. Well defined as the 12v supply actually being within 10% of its >rated voltaage. ;-( > >With no load the thing goes into over-voltage trip mode. With a small >load of 1/2A, it does power up. It just has poor regulation on all >supplies. Many I've seen do this in one way or another. AT&T supplies manufacturered by Altec have a heat-sinked resistor across the 5v supply. However, they will -sometimes- power up without any load, though I haven't looked at the output on a scope. Most IBM supplies, particularly from AT's work fine without a load. However, the old AT's had a heat sinked resistor between 12V+ and ground that was used if there was no hard drive installed. I've used an AT power supply to power 12 volt devices (HT's, test equipment, etc.) and have never had a problem even though I had no load on the 5V side. By the way, BEWARE OF OLD AT SUPPLIES! There are quie a number of them still out there. If you turn them off and then turn them back on quickly, they seriously lose regulation. I learned this the hard way, but not before doing it twice. First time it cost me a hard drive controller and an EGA card, the second time the system board :-( I've heard many other horror stories to the same tune. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104