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Guide How To: Bench PSU from ATX PSU

Discussion in 'Modding' started by JazX101, 24 Feb 2007.

  1. JazX101

    JazX101 What's a Dremel?

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    Lo!
    Jaz's Modded Bench Power Supply!
    Standard disclaimer; you loose body parts, senses, equipment, life etc. while attempting any of the following it's not my fault, and you should have been more careful. Rite, that said...
    Dirt simple mod really:
    Find an ATX PSU, find a piece of wire and put one end in the green wire pin on the 20 way ATX connector, stuff the other end in a black wire pin (ground). For those technically minded shorting pin 14 to 3, 5, 13 or 15. There are others but they are right next to each other so its easier! For those who want pixxies!!
    Put some tape over it so it doesn't accidentally short against anything else.
    [​IMG]
    Plug the PSU in and turn the power on whilst keeping a safe distance lest it explode, burst into flame, or other things that are bad for short-term not-dying-horribly.
    If the fan comes on and none of the above mentioned bad things happen then you have you're self a PSU that works, and will work as a bench supply, though at low load the lines may be a little off.
    Unplug it from the mains and give it some time to discharge. Easiest way I've found is to leave a fan or something on one of the Molex plugs, and it sucks the last of the power.
    Open the case and note where the capacitors are, for future reference AVOID TOUCHING THEIR TERMINALS as they can still hold a charge that will make you wish you hadn't, if not something notably worse. The capacitors are the black cylinders towards the front left.
    [​IMG]
    Unscrew the mounting screws holding the circuit board (PCB) in place. You might find a short black wire attached between one of them, this is important as it grounds the case to the circuit, safety and what have you.
    Looking on the circuit board its self, you should find some writing, R then a number etc. These are the component ID numbers. Look towards where all the wires join to the board, you should see markers for ground (GND), +12V, +5V, +3.3V. Elsewhere on the board you should see one for -12V, at the base of a brown wire if you want a hint.
    [​IMG] [​IMG]
    If you're unlucky and the board is blank, then the ATX spec matches wire colour with their voltage.
    Ground is Black, +12V is Yellow, +5V is Red, +3.3V is Orange, -12V is Brown, -5V is Blue. If you cant see anything even vaguely like I'm describing you have your self a PSU that was made too cheaply, go find a slightly better one!
    The easiest way is to unsolder all the wires of the existing cabling, then just attach those to you're connectors directly to the board. You really don't want to be messing about with sticky tape and bent wires in here, as bad things will happen, and that is usually expensive.
    For connectors, you want something that is not connected to the mounting. I noticed that a Maplins had some 2.5mm mono panel mount sockets going for silly cheap prices, and they were ideal. Solder you're newly reclaimed pieces of wire (sticking to appropriate colours if possible, in case you want to tinker at some point in the future) to the insulated contacts of your connectors.
    [​IMG]
    Mark out and drill holes for your connectors and on switch. Make sure they will not foul the heat sinks when you close the case, as they are usually grounded ( lots of sparks, no juice out and a dead PSU). Mount you're connectors, then solder the other ends of you're wires to the correct power pads on the board, as you identified earlier by one way or another. I suggest adding one of the Molex strands in again, as it can be really handy to attach to devices outside the case.
    [​IMG]
    Solder the green wire to one terminal of a SPST (on/off) switch, and a black wire to ground to the the other, this will replace you're bent paper-clip or whatever it was that you tested it with. This will give you 2 “power switches”, which I find quite handy. If you don't want a second power switch then solder the green wire to ground, that way the power supply will turn on as soon as you throw the power switch.
    Make sure you label you're connectors so you know what voltage you are getting out when you connect stuff. I used a engraving bit and had a bit of a play (not all that successful but it does well, and unlike a sticker or pen it wont wear off)
    [​IMG]
    Screw the entire thing back together again, including any ground/earth connections. Make sure that both (or not) power switches are off. Plug it in, then throw the switch. Preferably do this with something non conductive, as if you accidentally attached the case to one of the rails, juice will flow into you, which is not nice!
    If all looks good, find some old hardware, or the fan you were playing with at the start and plug it into the Molex to test if things are all going to plan.
    Its usually pretty obvious if things have not worked, but you may occasionally find that one connector doesn't work, which is probably due to soldering. Easiest way to test is with a multimeter, if you have one, and if not, why are you making a bench PSU if you don't have a multimeter?? Go get one!!
    Enjoy you're new desk based power supply.
    If you want to change the fan, either use the solder pads that the old fan used, or hook it to +12V and ground, (red for +12V and black for ground, the yellow is a sensor wire, so just snip it off)
    I've used mine to power circuits, test stuff for automotive use (motorbikes not cars, who needs all those extra wheels), power a haxxed LCD monitor that had eaten 2 power blocks, spin up hard disks without cases on (they were dead already, and are certainly dead now, but was a lot of fun) and all sorts of other things.
    Keep a Molex cable, its REALLY usefull!
    [​IMG]
    Same as having 2 power switches (less nasty surprises)
    [​IMG]
    Testing new indicators for my motorbike.
    [​IMG]
    No pix of the haxxed monitor yet, but soon :)
    Jaz_knos
     
  2. GuardianStorm

    GuardianStorm Minimodder

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    nice guide :)

    MY Bench PSU
    with a guide now, maybe more people will build them :)
     
  3. mattthegamer463

    mattthegamer463 What's a Dremel?

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    How so?

    Heres my Bench PSU mini-project log.
     
  4. JazX101

    JazX101 What's a Dremel?

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    Do you own one?? have you experiacned the warm fuzzy feeling of not having to hunt for batteries to test something :D
    Try the dark side.... you might like it.
    Jaz_knos
     
  5. JazX101

    JazX101 What's a Dremel?

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    Just found this again so:
    for those of you who want to test start you're PSU in the most professional and safe way possible, this product may be for you.
    LMAO
    Jaz_knos
     
  6. Duste

    Duste Sierra my delta, bravo!

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    If you read my first post, I made a simple statement, and two people asked me questions, and I elaborated. I did not intend to trash this thread, and still do not.


    Then let me suggest you STFU. Next bit of trolling and you go stand in the corner.
     
    Last edited by a moderator: 3 Mar 2007
  7. Argonautz

    Argonautz What's a Dremel?

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    nice, that is handy! Good work dude!
     
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