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
    1
    0
    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
    163VDC
    20.6A
    248.4W

    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:

    http://www.ebay.ca/itm/LM2577-DC-DC-Boost-3-30V-4-35v-Adjustable-Step-up-Power-Supply-Converter-Module-/300984906623?ssPageName=ADME:L:OC:CA:3160

    http://www.ebay.com/itm/10-32V-to-12-35V-6A-Step-Up-Voltage-Charger-Power-DC-DC-Boost-150W-Converter-/321345043216?ssPageName=ADME:L:OU:CA:3160

    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

    total
    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

    Expert

    Nov 30, 2010
    16,257
    6,757
    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
    611
    120
    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!
     
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