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need help converting an ATX PSU to bench power supply.

Discussion in 'Power Electronics' started by driftstardude, Dec 8, 2014.

  1. driftstardude

    driftstardude

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    Dec 8, 2014
    Hi I'm trying to convert a ATX to a bench power supply. the ATX that I'm using is:
    RAIDMAX Cobra RX-400AF-B 400W ATX 12V v2.3/EPS 12V SLI Ready CrossFire Ready 80 PLUS BRONZE Certified Raidmax RX-400AF-B Power Supply

    I cut all the wires and currently the orange to brown and blue to black are connected via buyt t connectors and wrapped with electric tape.

    Im waiting on supplies and wanted to know what to do next.

    I'm a tad confuse about the yellow wires. Some have a black stripe on one side.

    Thanks!

    This is to power up a lipo battery charger to charge a Rc car. A hitec 4channel lipo charger
     
  2. davelectronic

    davelectronic

    1,079
    12
    Dec 13, 2010
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,192
    2,694
    Jan 21, 2010
    Check that your power supply will work without load. Some note their *minimum* load. If it says something to the effect of "Minimum load 0A" then you can just use it. If it doesn't, you may have to experiment with loading one or more rails to ensure that they all go into regulation.

    Also, my preference is to leave the connector attached and use a mating plug for it. This allows you to change out the power supply easily if you need to later on.
     
  4. driftstardude

    driftstardude

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    Dec 8, 2014
    I'm a bit confused. How will I know it can work without load? Never tried this before. Y know it says something dash 18v on the lipo charger. Can I combine all the red wires together? Its a lipo charger designed to charge four batteries together simutanleously.

    Are any of the color wires negative? It seemed odd that a few yellow wires have that stripe.
     
  5. Bluejets

    Bluejets

    3,519
    714
    Oct 5, 2014
    Turn it on.
    If the internal cooling fan runs, then you are away.
    If it just give a slight "kick" and then stops , there will be additional mods to do.

    A photo would be helpful, top and bottom.
     
  6. driftstardude

    driftstardude

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    Dec 8, 2014
    The only purpose I have making a bench power supply is to power up an rc lipo charger. The psu has matching colors with the car, which I liked lol.
    [​IMG]

    Using butt connectors, the orange wire is connected to the brown and one of the black wires are connected to the green wire.

    Here in my hand are the yellow wires with the black stripe on them:
    [​IMG]

    This is what the specs said on the back of th[​IMG]e psu box:

    This is what it says on the side of the lipo charger:
    [​IMG]
     
  7. Bluejets

    Bluejets

    3,519
    714
    Oct 5, 2014
    I do believe you have your connections completely wrong so..........

    Show what you have connected and for ****** sake, don't power anything up just yet............

    Note that pics of your model car, however taken you are with their appearance, does not help here.
     
  8. driftstardude

    driftstardude

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    Dec 8, 2014
    I was following a YouTube video and I wasn't sure if it was the right thing to do. What's connected are the two wires.
     
  9. driftstardude

    driftstardude

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    Dec 8, 2014
    One orange wire is connected to the brown wire. And one black wire is connected to a green wire. Everything else have been clipped. No other wires are connected.
     
  10. Bluejets

    Bluejets

    3,519
    714
    Oct 5, 2014
    Sounds to me like you are connecting into mains wiring which is potentially fatal.
    I asked you to show what connections you have made but if you cannot then I can only comment that you leave it to an electrician with experience.
     
  11. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Please note that the high voltage wires that come in from the socket in the side of the PSU should be avoided at all costs! Don't cut them, join them or touch them.
    The only wires you need should be bundled together and sent outside of the case.
    Identify these wires and ONLY use them, don't grab any other wire that resides inside the case.

    Please note that 'brown' is not a very common color on power supplies.. it is on some.. but unless you make sure you know what the wire is, don't tie it to anything.
    Do you still have the connector for the power supply? The part that mates to the motherboard?
    You can verify the colors by looking at a pinout for that connector. Colors are not a reliable method.

    The wires you should need are as follows, and will be part of the wire bundle that exits the PSU and goes to the largest connector.
    Yellow - 12V (Ignore the Yellow/Black stripe for now)
    Black - Ground (0V)
    Green* - Commonly green, not always! Labelled as 'PS-ON' when you google an "ATX pinout"
    Please grab a meter and test these wires before using them. They are common colors... but you must always be certain.

    I won't give more details until you provide more details.
     
  12. driftstardude

    driftstardude

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    Dec 8, 2014
    This is the youtube v
    ideo I was following, , but after awhile I decided to stop and came here to see what to do. Their are three brown wires, one short one leading from the socket to the power switch. Then a second short brown wire from the power switch to the circuit that has a 'L" next to it. The brown wire I used (as told in the video) leads to something covered in glue. +something vs. That brown wire is conected to an orange wire leading to the +3.3V section.

    The green wire appears to be relating to power, it leading to a part of the circuity that is covered in glue. somehitng j37 and "on" on the bottom.

    here are some pictures:
    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  13. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    OK. well, one of two things will happen... You have either grabbed the wrong brown wire and you're in for some serious potential damage / injury... or you grabbed the correct brown wire.
    Can you please confirm that the brown wire used, was the one that went to the large ATX connector for the motherboard?
    That's my biggest concern right now.

    As far as the green wire is concerned, please check for the same... ensure it was the same wire that went to the connector you were told to chop off.

    What you're doing is pretty dangerous... especially when following the youtube video you linked. That guy seems to know just enough to be dangerous.
    The voltages present inside that case are 110V, but there are also some pretty large capacitors that can store more than enough energy to kill you. When you dive into anything electronic, be sure to do as much research as possible, and please don't assume it's safe if you see it on youtube.

    If you can please confirm and be certain about the questions I have asked, then you should be good to go. Otherwise if you're not sure, hesitant, or not 110% certain you grabbed the correct wire from the ATX connector that you disconnected, then please put that power supply aside and don't continue until you can get a little more information.
     
  14. driftstardude

    driftstardude

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    Dec 8, 2014
    The green and brown wire were from the main cable that plugs directly into the computer. After I connected those wires and the next two wires, I begain disconnecting everything, meaning I cut them all down into wires. That was when I stopped following the video, because I wasn't sure if what he was doing was right, and I wanted more help in the matter.

    I used butt connectors and crimp them togehter abnd wrapped with electric tape, I am considering soldering them instead.

    Their is only one green and one brown wire that was part of the other cables leading out of the box. The oteh brown wires are connected directly to the switch and circuit internally.

    Curiously, what is the worse thing in that video? Their's another guy on youtube using a paperclip at the end of the atx cable, that worried me the most.
     
  15. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    The part that concerned me in the video was from slight mistakes as he described the unit. It convinced me to a great degree that he know 'just' enough to use it as a 12V source... The video itself was sound, and to be honest, I literally just finished testing a 12V LED driver with an old power supply I had laying around... I simply stuck the wires into the end of a molex connecter, then used a small piece of wire and crammed in in the end of the ATX connector to join the green and black wire.
    The wire's he has you messing with are low voltage sense wires. Green is 5V I believe and when pulled to ground the power supply turns on. The brown wire could have been connected internally and if that was the case I would be greatly concerned to be certain you have the correct brown wire. However, because the brown wire you are using was originally tied to an orange at the ATX connector what you have done is solid.
    Finish your project and enjoy, just make sure you can isolate the yellow wires from the case. Those little rubber grommets used in the video may wear over time as you use it. If it shorts to the chassis, the power supply will most likely 'fault' and shut off.
     
  16. driftstardude

    driftstardude

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    Dec 8, 2014
    Im still waiting on a few items to arrive. My concern is that the item I'm gonna to use this PSU for says 18v on the side? But the instruction videos to modify the PSU would say 12v?

    Thanks for everything thus far!
     
  17. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    The video shows a device with an input voltage 'range' that included 12V.
    Take another look at your device.
    Does it say 12V-18V ? Or just 18V?
    The PSU will give you 12V almost exactly... so if your device is set for only 18V there may be an issue. If in doubt, you can snap a pick of the device so we can see the sticker/label stating the requirements.
     
  18. driftstardude

    driftstardude

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    Dec 8, 2014
    The lithium polymer charger says "DC input 11-18v". Its possible to charge four different RC batteries such as nmhi, lipo etc.
     
  19. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    Perfect. So you can use anything with the range of 11 to 18V
    The 12V output of the PSU falls into this range. So you're fine for voltage. Just make sure the input 'current' demand is less than the power supply. (I think you have 20A to play with though... and I doubt your charger is going to put 250W into your batteries.

    You should pretty much be able to wrap it up when you have all your parts and call it done.
     
  20. driftstardude

    driftstardude

    10
    0
    Dec 8, 2014
    Hi,

    I think I finished putting everything together. My soldering iron and other supplies came in. The black strip on the yellow wires was just a 12v2 and the other wires were 12v1. I used 4 reg. 12v1 and solder them together. Took 4 black wires and solder them too. Did the same using 4 5v wires and another 4 black wires. I solder each of the four sets to these bannana connectors. So I have 2 ground outputs, one 5V output and one 12V output.

    The other wires were tapped at the end with electric tape. I'll post pics when I can.

    I do have a question about resistors. I have a resistor connected to a black wire and a red 5v wire. The video I was watching that talked about resistors said a slightly different model. The one I got from Frys says:
    NTE10W010 L F
    10W10 Ω 5% 143B

    Is this a good resistor to use? Thanks!
     
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