12V 1A from ATX supply?

Discussion in 'The Projects Forum' started by Chip2786, Sep 14, 2010.

  1. Chip2786

    Thread Starter New Member

    Sep 14, 2010
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    Hi, Ive been building Pc's for years but never really dived into the minefield of PSU's,

    My question is... Is it possible to get a 12v 1A draw from an ATX PSU and if so, where/ what cables can I take it safely and what components do I need?


    Here's why, I have a external network card that requires its own power source (Input 100-240V-50/60Hz 0.35A, Output 12V 1000mA) but I would rather it ran off my pc's supply as im mounting it inside my pc (dont ask why just fancied a project)

    any help would be amazing

    Regards,

    Chip
     
  2. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Very easily done. Do you have a spare HDD power plug coming from your PSU? If so the yellow wire is +12V and black is GND. You can just use those with an old mating connector (i know you have heaps laying around....don't we all) hooked up to the DC socket of your network switch.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    Here is a link to the cable pinout - http://wiki.xtronics.com/index.php/ATX_Pinout As to being able to pull an additional one amp is unknown. It will depend on the existing load and the PSU's rating. Your hard drive and DVD drive both use +12 VDC already, as do chassis fans.
     
  4. Chip2786

    Thread Starter New Member

    Sep 14, 2010
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    See thats exactly what I thought but.. I tried it and it killed my router lol, luckily i have a spare :)

    Unless I put 12v to -ve on the router by accident?

    hmmmm

    ill go play and report back asap :)
     
  5. Chip2786

    Thread Starter New Member

    Sep 14, 2010
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    The PSU is rated at 700W not sure on ampage tho but ive only got 1 case fan, 1 hdd and 1 dvd drive to run so it hopfully will be ok what fuse shall I use so as to not break another router, will 1amp do? or will I need less? im guessing a fast-blow would be safest?
     
  6. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    I would probably go for a 2 amp slow blow or 3 fast blow. I honestly think if you have got the polarity right it should be fine. Did you check your wiring?
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    If the router's input polarity isn't clearly marked on the back of the unit and you have no access to a schematic I'd open it up and trace down which input pin is + and which is -

    Chances are one of the first things the power input lines hit is a polarized electrolytic cap.
     
  8. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Also if you have it opened up the negative is "generally" the track that goes to the largest area. If you can find the negative terminal of any component (polarised capacitor is easiest to find) buzz it out with your multimeter.
     
  9. sceadwian

    New Member

    Jun 1, 2009
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    Chip... You don't have to dive into anything, try reading the label =\ An ATX supply will have the listings of what current's it's capable of on what rails right on the case.

    I have an older 350W ATX I use as a bench supply, the 12 volt rail will do 16amps. Modern ATX specs rely on 12V more and you can get some pretty dramatic amps off the 12V lines of those. It definitely sounds like a reverse polarity with the router, too cheap to add polarity diodes on the DC power input =)
     
  10. windoze killa

    AAC Fanatic!

    Feb 23, 2006
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    Good point about the diode. I always put one in line with all my new projects because humans are dumb animals (gee, I think I have said that somewhere before) and will make mistakes. Nobody is perfect and those that say or think they are really are just FIG JAM. Anyway back on to the subject..... I have actually made up a power distribution box that has a heap of outputs all passing through 20A schotky diodes. This has avoided the arc welding results I have seen in the past.
     
  11. Chip2786

    Thread Starter New Member

    Sep 14, 2010
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    0
    Hello people, It was just the polarity. I opened the router up and solderd my psu direct to the board (via a 2 amp fuse) and it worked :D cheers for all your help ur all stars

    Love chip
     
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