EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: IllNate on May 01, 2018, 02:31:51 pm
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If you're having trouble with this kind of project, you may find that the purple wire (5V always on), needs a miniumum load. The OCZ 600W supply I used required a load here to 'trick' the supply into turning on, without a motherboard attached.
Now that I've completely exposed my lead, I'll explain. I'm actually not making a benchtop supply (since I have an adjustable one already). I'm using it to power a 3D printer I recently purchased. But I wanted to see how well it regulated the +12V line under load. But I could not get the supply to turn on. I found a data sheet which suggested minimum loads for the different rails, which I dutifuly followed. But nothing worked. I eventually gave up. Then an old computer was getting scrapped, so I hooked up the PSU to that, just for my own sanity. That worked, so time to revisit it again. While I was trying various combinations of load, I noticed the +5V always on line, stayed high for quite a while after switching the supply off. As I wanted to repeat my sequence from a truly off state, I threw a 10 Ohm load on there as well, and voila, it worked. No minimum loads required on the other rails at all, unless you want good voltage regulation. For example I found that after loading down the 12V lines with 120W each, I required a load on the 3.3V rail, otherwise the 12V rail would droop (probably meeting some 3.3V overvoltage condition).
Other caveats: Short green to ground to turn on. Brown wire is 3.3V sense, so connect this to orange wires.
Anyway, I ready many tutorials on benchtop ATX conversions looking for hints and did not come accross this hint. So I'm posting here (as well as a few comments on these tutorials) in the hopes it will help someone else.