Newbie Help - ATX PSU for multiple devices

Discussion in 'The Projects Forum' started by cannonjack, Apr 9, 2014.

  1. cannonjack

    Thread Starter New Member

    Apr 9, 2014
    Hello all, I am a newbie to electronics and require some guidance.
    I have been working on organizing my wiring closet and would like to streamline the nest of wall warts to the myriad of devices I have for the house and my computers.

    The goal is to power 10 DC devices with a spare ATX PSU I have lying around.
    The devices and the rated power requirements as per their labels are as follows:

    kvm switch - 5v @ 0.5a = 2.5w
    dlink router - 7.5v @ 1a = 7.5w
    dlink nas - 5v @ 3a + 12v @ 3a = 51w
    coax splitter - 12v @ 0.5a = 6w
    5x40mm fans - 5 x 12v @ 0.25a = 15w
    qnap nas - 12v @ 5a = 60w
    voip modem - 15v @ 1a = 15w
    cable modem - 15v @ 1.2a = 18w
    lcd monitor - 19.5v @ 3.8a = 74.1w
    poe injector - 48v @ 0.35a = 16.8w

    total power load

    I will have to measure the actual voltages and amperage of the devices to verify these figures.
    Can I power the 5v and 12v devices straight from the atx psu or will they require additional conditioning?
    For the devices with other voltages than 5v and 12v I am thinking of using boost converters as per below:

    From my limited understanding, boost converters momentarily increase voltages to the desired level.
    Will these be safe to use on devices that require a constant voltage?

    Some of these converters have a max input current as well.
    Will connecting to a 12v 18a psu rail fry these converters that have, lets say a 10a input max or is it based on the amperage draw from the load?

    The atx psu I am planning on using is a 560w supply.
    +3.3v @ 34a = 112.2w
    +5v @ 35a = 175w
    +12v @ 18a = 216w
    +12v @ 18a = 216w
    -12v @ 0.5a = -6w (is this correct?)
    +5vsb @ 2a = 10w

    amps = 107.5
    watts = 723.2

    Am I missing something, are the 2x12v rails actually one rail?
    Even if this is the case, the total watts would become 507.2w (560w-507.2w=52.8w).
    Where did the extra 52.8w go? I am guessing I will also have to measure actual Volts and Amps of the PSU.

    Even with a 500w ATX PSU I should theoretically have enough Watts for my devices, overages included. (just not all from the 12v rail)

    Thoughts and suggestions greatly appreciated.
  2. #12


    Nov 30, 2010
    Lots of questions!

    1, yes.
    2, boost converters aren't momentary.
    3) no.
    4) The power supplies use multiple wires to deliver current for a single voltage because there is a limit to how many amps you can send through one hole in the thin copper in a circuit board.

    aaand...there is a minimum load on one of the voltages. Somebody else will tell you which one and how much.
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
    I'd just like to add that I hope it's a decent quality ATX power supply because you open yourself up to multiple device damage should it fail!