Monday, 4 March 2013

My PSU Project.

I decided that it was time to set up a cleaner, more permanent solution for providing 5V and 12V in my server rack. Here's some photos with details outlining where I'm at so far.

4 x 20A rated terminal blocks. 2 of them are for +5V and +12V. The cable I used is auto stuff rated for 10A. I split common ground (GND) over 2 terminal blocks so I don't overheat cabling. Also saves device cabling from reaching.

Rear shot of where terminal blocks are secured in rack.

550W ATX PSU with +5V, +12V and GND feeds. The PSU is getting 240V straight from my UPS (to the left). Those terminals off the feeds are high quality gold plated banana type terminals with plastic covers.

I need to clean up the wiring a little bit. A few additional things to do:
  • Get 10A in-line fuses for +5V and +12V. Although PSU is current limiting (shuts off when over current), I really don't want to get to this stage.
  • Put a permanent resistor on the +12V circuit. Although I'm constantly pulling something of +12V, I noticed very weird behavior on the +5V when there is nothing doing so. I believe this is related to the PSU needing current draw on +12V in order to function properly.
  • Get a cover for the terminal blocks and some sort of support for device cabling.
  • More cable clean-up.
  • Shunt for reading current draw on +12V and +5V circuits.


  1. Hi Daniel.

    I totally understand the need for this project (another story).

    Sorry to appear dim but I don't understand some of the following (highlighted by chevrons) >>> "Although I'm constantly pulling something of +12V <<< I noticed very >>> weird behavior on the +5V when there is nothing doing so. <<< I believe this is related to the PSU needing current draw on +12V in order to function properly."

    What are you running off the 12V rail? Although that should not be important ...
    What kind of weird behaviour on the 5V rail do you mean?

    FWIW I suggest using that PSU on a "proper" PC running e.g., Windows and something like Speedfan that gives total visual GUI info about voltages etc etc?

    Cheers, Ray

  2. Hi Ray,

    Running a router off the 12V.

    I believe the weird behavior is voltage drop. Haven't tested. I believe most ATX PSUs need current draw on 5V or 12V in order to function properly.

    RE: PC for monitoring voltages - That's a good idea.



  3. Hi Daniel.

    I've only ever seen serious 12V voltage drop when I used a really poor ATX PSU and when things are getting heavy-duty - like running a Gallatin flat-out and/or a heavy duty graphics card @100%.
    The 5V line seems pretty constant. See where image "Idle" vs image "Busy" means nowt for the +5V line & serious vdroop on the +12V line (ignore the -12V & -5V readings as they have never been accurate using this motherboard.)

    Kinda lateral thinking but anyway ... I saw a 12V-to-5V DC adapter somewhere on £bay. Would that solve the ATX PSU 5V-needs-a-12V-load issue, if there is such an issue???

    HTH, Ray

  4. Hi Daniel.

    I said "I totally understand the need for this [PSU] project (another story)."

    Here's a quick follow-up on that other "story"
    The 5V 10A PSU that I suggested seemed OK. I then ordered another 2.
    Before I set up the 2 newer PSUs the first failed (it lasted about a month. On enquiry the supplier "engineer" said these PSUs would fail after a month if left on 24/7.

    Preposterous/hilarious - take your pick.

    After about two months I can confirm that the 2 newer PSU's are currently 100% OK running 24/7.
    One detail - the failed PSU motherboard upper surface is 100% green - the newer PSU motherboards are both 100% beige (I swear they were 100% red when delivered(!?).

    I hope your 5V 20A PSU is OK :)