I decided to make a new power supply tonight outa some old AT power supplies i just got my hands on. Two were burnt out, but one, a 200W one was still functional.

Im planning on putting some metering in and wrapping it all up in a bigger box, with bananna plugs.. but i was surprised by just HOW MUCH LOADING you need to put on the 5V -> ground, just to get the +/- 12 V DC balanced and running at what they say they are!

I check on a web page, and it said approximately 2A on 5V. Wow! Do the math here and you get 2.5 Ohms, 10 Watts! Just as an internall operating load (so you can then after connect at will for test benching!).

Too be honest, im hard pressed to find any resistors that low and at that wattage. I even tried (only as a test) to connect a 100W light bulb to see if it will load the 5V rail enough to get 12V up to par.. It got me to 11.5V and -10.8V... still not close enought. (( Looks like im off to the AutoMotive shop tomorrow to buy some resistors ;) ))

Thought i would post it for converstation.. nothing more ;)

:alright:
NaN
Posted on 2003-06-01 00:25:16 by NaN
hi NAN !
nice idea !
about the PC Power Supply, i think it's one of the first trouble of today PC crashing.
If to many peripherals are attached it can sit down, and pc can go in to paralizing.
Same thing if power supply come old, 3/4 year of working, electrolitic capacitor can go into leakages, lsome voltage could be no more really stabilized, you can be at risk.
More than one time i've discovered paralizing troubles disappear replacing PS with a new one.

Some time ago i've try the following solution. Two 200W power supplies 220V serial connected: i've fixed them in front of the case (where CDROMS stay, it's quite the same width (PC has a great look/scene :) ). So then i've attached some peripherals to the first one, MB and others HD to the second one. Obviously, grounds connected togheter and same neutral pole. It works pretty good. :) :)
Posted on 2003-06-04 02:39:31 by Bit7
you'll be my hero if you make a perfectly silent one (fanless) :grin:
Posted on 2003-06-04 04:02:52 by Hiroshimator
Hi, NaN,

Unfortunately there isn't much you can do to improve the cross-regulation on this kind of supplies.
I could tell you how to do it, but that involves modifying the power supply, and we are talking big modifications.

That is a really complicated thing, so I think you are better off with just adding a couple or automotive bulbs to the +5V output.
Posted on 2003-06-04 11:45:15 by VVV

I check on a web page, and it said approximately 2A on 5V. Wow! Do the math here and you get 2.5 Ohms, 10 Watts! Just as an internall operating load (so you can then after connect at will for test benching!).

Too be honest, im hard pressed to find any resistors that low and at that wattage.
Resistors that low and at that wattage exist in wirewound form.
Posted on 2003-06-04 16:39:07 by tenkey
Thanks for the advice everyone. I dont think i will put light bulbs on the supply :) , but i will get a good high power resistor. Next time im out at the computer recyclers or something..

I personally was more or less surprised that a computer will pull this much current load by defualt. Its no wonder that the CPU gets so hot, i guess i just never truely put one and one together in this respect ;)

:alright:
NaN
Posted on 2003-06-04 22:53:30 by NaN
You might also use several resistors in parallel if you just can't find high-watt resistors...

In fact the 'test' for the power supplies we built for school projects was 10 10-ohm resistors in parallel, all of them 1-Watt resistors (little white rectangular ones).
Posted on 2003-06-13 11:27:31 by AmkG
Actually that was what i did to initially test it. I twisted a roll of 10 Ohm 1/4Watts into a tootsie roll, and used alegator clips to test with. Even then they were getting hot (but i didnt leave them connected long enough to damage them).
Posted on 2003-06-14 20:47:06 by NaN