as the title suggests I am trying to use an ATX power supply (Seasonic modular X-1050) as a stand-alone power supply. I have roughly followed guides available online, the best of which I have found to be this one on Instructables.

I have PS_ON (green) grounded to 0V (black). Once this is grounded, I switch on the PSU and the fan spins up and it briefly outputs +12V and +5V (I haven't checked other outputs) for less than 1 second. I have also tried this with PS_OK connected to +5V. The PSU then turns off until I unground PS_ON and reground it.

I have also tried the above, with the addition of a load on the +5V rail, namely two USB devices I had lying around (iPod touch and AA battery charger) and 1 laptop HDD. I estimate the load to be ~1.2A or equivalent to a ~4.2Ohm resistance.

How do I get my power supply to stay on? Do I need additionally loads on +3.3V or +12V? Thanks

  • \$\begingroup\$ I can't speak for one that's torn open like this, but when I'm using one as an actual PC power supply I just use a paperclip to bridge the two pins in question and it'll stay on the whole time. It may be that having the 24 pin ATX connector still attached actually adds something to the equation. \$\endgroup\$ – Shinrai Jul 22 '12 at 19:43
  • \$\begingroup\$ Also, I'm not sure you'll get a very good answer on SU...maybe Electrical Engineering.SE? \$\endgroup\$ – Shinrai Jul 22 '12 at 19:43
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    \$\begingroup\$ The USB devices won't start drawing their full current even if you connect them directly. Instead, they'll try to negotiate for current and that won't happen. The apple devices also won't accept current from unidentified chargers. Try using high power resistors to provide a load for the power supply. \$\endgroup\$ – AndrejaKo Jul 22 '12 at 20:53
  • \$\begingroup\$ I think this post is talking about exactly what you said :) doayee.co.uk/getting-an-atx-power-supply-to-run-outside-a-pc \$\endgroup\$ – user26895 Jul 29 '13 at 22:35

The problem was that I shorted PS_ON to ground without the cables connected to the power supply (it is a modular PSU). The voltage sense wires were not connected to their corresponding partner because the cable was not in place. Hence, the PSU thought the voltage was off and shutdown.

The solution was to look at the pinout, and see which +3.3, +5, +12, and ground pins overlapped on the ATX cable. I shorted those to each other (+3.3 <-> +3.3, +5 <-> +5, etc) and now it works great!


Most likely the case is that the PSU in question requires a load on its rails to function normally. As AndrejaKo mentioned, you should try using high-power resistors to supply a load for the PSU instead of other devices. Definitely load the +12V rail and the +5V rail (can't hurt to load the +3.3V rail as well).


Most switching power supplies require a load to stabalize. Try to put a light bulb or something on the output, it should work.

  • \$\begingroup\$ Thank you for the response. This was not the answer. As I mentioned in the question, I tried attaching a load. The answer ended up being that the voltage sense wires were disconnected \$\endgroup\$ – Streblo Mar 19 '13 at 1:11

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