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I have an old PSU, model LPK9-4P. I'm trying to power an Arduino project with it, but it doesn't work as expected.

PSU is wired with a switch between signal and ground, and powers on well. Measures shows voltage in every line. But 12V line, with just 2 fans on it, just works few seconds before falling down.

5V line is stable and working, powering arduino and a bunch of sensors.

Is this about load requirements? A malfunctioning PSU? I'm kind of stuck with it, and it's just a testing power source!

Photo of PSU label

Photo original on Google Drive The photo is the only data I have about this psu.

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  • \$\begingroup\$ What does the data sheet for the power supply tell you? No data sheet = no help unfortunately. \$\endgroup\$ – Andy aka Nov 11 '16 at 17:24
  • \$\begingroup\$ Have you connected the PS_on Line to ground? the green wire in the ATX harness. \$\endgroup\$ – ambitiose_sed_ineptum Nov 11 '16 at 17:30
  • \$\begingroup\$ Yes, it's connected with a switch to easily on/off. \$\endgroup\$ – David P. Nov 11 '16 at 17:33
  • \$\begingroup\$ drive.google.com/file/d/0B9zqdJulDgw1UmhrdmlZZHVpTVU/… this is the only data I have about this psu. I can't find nothing online. \$\endgroup\$ – David P. Nov 11 '16 at 17:37
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[...] 12V line, with just 2 fans on it, just works few seconds before falling down.

5V line is stable and working, powering arduino and a bunch of sensors.

Is this about load requirements?

It is impossible to be sure without a proper datasheet. However, this might be the problem, because some PC PSUs do require a minimum load on their +12V rail for correct operation. The two fans you mention as the only load on the +12V rail, would not meet the minimum load requirements for some of the PSUs which I have seen.

Without whatever minimum load a specific PSU requires, the +12V rail may fluctuate or may even rise enough to trigger over-voltage protection, and other rails (including the +5V rail) may also be out of regulation.

To test this possibility, connect a car headlight bulb (e.g. 50-60W) to the +12V rail to draw around 5A and see if the bulb remains lit. If it does remain lit, then that confirms your specific PSU requires a minimum +12V load.

Update: Of course, another possibility is that your PSU has an internal fault.

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  • \$\begingroup\$ Tried. And it doesn't work, same problem. Thanks for the tip, I will keep in mind to test future scavenged psu's \$\endgroup\$ – David P. Nov 12 '16 at 19:54

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