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Converting Computer ATX Power Supply to Lab Bench Power Supply

Discussion in 'Electronics Videos' started by ElectroMaster, Dec 16, 2011.

  1. ElectroMaster

    ElectroMaster Administrator

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    Converting Computer ATX Power Supply to Lab Bench Power Supply

    Description

    Small tutorial on Computer ATX Power Supplies. How to use them, how to connect them in series, in parallel. What is 12V rails? Is it possible to connect 12V rails together? ATX connector wiring explained. What is difference between old computer power supplies and new ones? And finally how to make Lab Bench Power Supply from Computer ATX Power Supply.



    By JumperOneTV.
     
    Last edited: Sep 10, 2013
  2. mvs sarma

    mvs sarma Well-Known Member

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    Very educative, ElectroMaster. Thanks.
    Especially the bit of info that modern ATX come with higher capacity on their 12V rail. Good Video.
     
  3. cr0sh

    cr0sh Member

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    This was a great video, but I do have one big issue with it: His drilling "technique":

    1) You should -never- use a power drill while holding the part being drilled by hand. If the drill should catch or slip on the material, things could get nasty (I've learned that lesson the hard way more times than I can count - I guess I am a slow learner!)

    2) When modifying a case, you should remove all electronics from the case first, then reassemble after modification (I don't know how none of the chips/swarf from drilling out those holes didn't short out the power supply, but by disassembly, you can make sure the supply is clean of this debris before re-assembly)

    I did like that small heat-gun (or SMT resoldering station? Couldn't tell) he was using - I wish I had one for my bench...
     
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  4. dave

    Dave New Member

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  5. RCinFLA

    RCinFLA Well-Known Member

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    Couple of little bit falls. He talked about placing a minimum load dummy resistor on either the 5v or 12v rails. This is because the primary feedback for voltage regulation is accomplished on these rails (5v old, 12v new supplies). Without them the power supply will likely be unstable.

    He did not mention the other rails' voltage is solely based on the transformer turns ratio of each winding of the secondary. There is no individual regulation control on these other lines. The primary control voltage regulation is only on the 12v supply for new power supplies. This make the voltage regulation on the other voltage supply outputs rather poor as their loading varies.

    The outputs are rather noisey due to the direct switching regulator output. I would not use them directly for any analog circuitry where power supply noise level is important. The audio circuitry on a computer motherboard has power supply filters and on board linear regulators to create a clean supply.
     
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  6. mvs sarma

    mvs sarma Well-Known Member

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    Perhaps in this case the regulation would be on 3.3V that draws more current, I suppose.
     
  7. harold777

    harold777 New Member

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    Drilling technique apart, it's a good use of an unwanted SMPS - but I'd like to know what noise is on the rails -
    For general use I like to have Plus/Minus 15v rails. That bit more than standard 12v so maybe use several SMPSs and Linear Regs to provide some variable element - but then sudenly it gets a bit larger and more difficult....

    I'm soon building a variable lab-psu and think I shall need conventional transformers - that way I can switch the LV (by turning off the primaries?) so the OP voltage is kept managabe. Heat in Linears is always an issue for long-term reliability.
    I bought some 2A 5v regulators which can beused at higher voltages to cut the noise, then into a 1.2v variable...Hey-Ho.
     
    Last edited: May 26, 2012
  8. Donalddon5

    Donalddon5 New Member

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    I know this is an old post but I think all of these converting ATX Power supplies are way over-rated. I simply just bought a old dvd/cd/video cd sharp dv-740 player from a junk sale for 3 dollars took out the entire first pc board and hook up some alligator clippers to it anytime I need power supply. It is so well built that noise is minimum and best of all it is already ready to go.
     
  9. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    What is your beef with them. I have a nice bench supply but the ATX comes in handy when I need more voltage sources.
     
    Last edited: Sep 22, 2012
  10. Donalddon5

    Donalddon5 New Member

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    No Beef. I have one also. But doing it the other way offer same thing without going through so much trouble. Just take out a couple of screws, plug in and hook up your alligators. Just wanted to let others know there are better alternatives and cheaper. It does make a nice weekend project, hope I did not sound rude.
     
  11. panic mode

    panic mode Well-Known Member

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    drilling with PCB in there? way too many places for metal shavings to get into....
     
  12. 3v0

    3v0 Coop Build Coordinator Forum Supporter

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    I have to agree with panic mode about the drilling.

    When I built mine I cheated and used Sparkfun's kit. The kit is $20 and you can buy the binding posts for under $5 so I would not recommend it if you are price sensitive.

    Instead of a load resistor I mounted a fan on top. As noted in my review of the kit the traces on the PCB could be larger so if you need full current it may not be the best choice. It works well for my use but if I had to do it over I would make a PCB with beefier traces and a switch. Sparkfun provides the eagle files for the PCB so the modification would be easy.

    [​IMG]

    I have a nice bench supply with current limiting that I use most of the time. The ATX supply is only used when I need more then 1 voltage supply.
     
  13. Leezygeezer

    Leezygeezer Member

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    Hi I would like to convert my old Atx power supply too but mine is different to the one in the original video, is has a 3.3v (30a), +5v(36a), +12v1(20a), +12v2(36a), -12v(0.8a), +5vsb(2.5a). It also has a fan and an isolating switch which will mean slightly less work. If I follow the Atx wiring from the video then the orange wires are the 3.3v, the red are the 5v, the yellows are the two 12v rails, black wires are ground, the blue is the -12. The remaining wires are purple, brown, grey and green, one of each. Following the video would indicate green is power on, brown is 3.3v sense and purple is 5v standby and grey is power good. So, which of the wires would be the 5vsb? Would that be the purple?
     
    Last edited: Sep 24, 2012
  14. edeca

    edeca Active Member

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  15. Evson

    Evson New Member

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    quitely great show... !
     

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