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ATX power supply to bench lab supply? help

Discussion in 'Power Electronics' started by AlenZGB, May 31, 2014.

  1. AlenZGB

    AlenZGB

    170
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    Feb 19, 2014
    I could use some tips on how to convert PC power supply to bench lab supply.
    i have some old 450w power supply, and my vision look something like this:

    Convert power supply to max 24V(if it can`t be done since its older one. then 12v is ok) with variable potentiometer and voltmeter lcd.
    So that i can use it to test/fried PIC that i manage to program, and for lots of other stuff.

    Any ideas would be nice.
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
  3. AlenZGB

    AlenZGB

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    Feb 19, 2014
    I try that, but was wondering if anyone have done it already and do something other then google instructions.
     
  4. Sadlercomfort

    Sadlercomfort Ash

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    Feb 9, 2013
    I've seen these tutorials, looks like a great idea. This guy looks like he knows what he's doing, nice quality to his work.

     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    A lot of those power supplies have very little room to safely add additional connectors

    My recommendation would be to get an appropriate "extension" for the power supply main connector then wire your terminals to that. This has the distinct advantage of allowing you to replace the power supply in the future if anything goes wrong.
     
  6. AlenZGB

    AlenZGB

    170
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    Feb 19, 2014
    I come across this construction.
    Just i want to do it without ammeter,only with voltmeter.
    and one only ground and positive connector.
    and potenciometer for regulation from 2v-24v
    cover it with some tape, like sticky carpet, i still got it when i made my subwoofer box.
    cover enough not to look like Bender from the futurama but leave holes for vents.



    [​IMG]
     
  7. davenn

    davenn Moderator

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    1,745
    Sep 5, 2009
    well you would need a boost convertor on either the 12V or 5V rail to boost it to approx. 26 to 28V
    Then another adjustable regulator, as an example, say a LM338 ( 5A max ) to vary that 28V between 2 and 24V

    ohhh and I wouldn't cover any of it with tape, they need all the ventilation they can get

    if you want it to look nice, remove the board, fan and mains connector and mount it in a better looking case
    that's to your liking

    Dave
     
  8. Rleo6965

    Rleo6965

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    Jan 22, 2012
    I'm also in the process of building Lab Bench Power Supply from 300W ATX PSU. I'm going to use it for my Car Electronic projects that the reason I have to modify the PSU circuit to have dc output of +13.8V. I also include the the ATX dc out +3.3V, -12V & +12V for Opamp Supply. Planning to have Variable DC output +12V to 2.5V using LM317 w/ 2N3055.

    Front panel casing was from defective PSU.


    Painted Panel.jpg
     
  9. Kiwi

    Kiwi

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    Jan 28, 2013
  10. AlenZGB

    AlenZGB

    170
    4
    Feb 19, 2014
    Maybe i read it wrong but shouldnt i get 24V when i connect something on -12V and +12V?
    But i wont get more then 3-4A or I read it wrong or the writer is wrong.

    @davenn
    Didnt ment all the ventilation to be covered, just metal parts that dont have ventilation points, it has 2 vents,
    plus they wont turn on all the time, they should turn on only when needed, more consumption of power or am i wrong?

    @Rleo6965
    Looking good, i kinda like this analog thing, but i already ordered the digital ones.
     
  11. davenn

    davenn Moderator

    13,246
    1,745
    Sep 5, 2009
    you are not going to be able to use the +12 and - 12V rails like that as they don't have the same current capability
    the -12V rail is usually very low current ... What is the rating for your -12V rail on YOUR PSU ?

    and added to that ... most adjustable regulators need at least 2V headroom, which is why I said you need the 26 - 28V into the adj reg.

    There may be some switching regulators that will work on 24V in and give ~ 2V - 24V. I haven't checked
    something for you to do :)

    cheers
    Dave
     
    Last edited: Jun 2, 2014
  12. Rleo6965

    Rleo6965

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    9
    Jan 22, 2012
    You can't use -12V and +12V to get +24V and its also low ampere.

    Kiwi
    have a better suggestion that you buy that DC to DC Converter and you connect it to the +12V with High Ampere capacity ( Yellow Wire ).
    http://www.ebay.com/itm/DC-DC-Conve...6A-/261049815695?ssPageName=ADME:L:OU:US:3160
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
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    Jan 21, 2010
    Some (many?) modern PC power supplies have multiple 12V rails.

    It is conceivable that you could take one of these and ground the positive side instead of the negative to get a high current -12V rail.

    This is easy in principle, but probably much harder in practice. You'd have to mess with a large groundplane and possibly insulate rectifiers from the heatsink.

    It would be a great hack though.
     
  14. Solidus

    Solidus

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    Jun 19, 2011
    Most PSUs that I know of at least do cursory isolation of much of their 12V supplies so that they are independent of one another. That's not to say each yellow/black wire is independent, but there are multiple supplies.

    The CPU derives its supply (anywhere from 2.0V to 1.0875V depending on manufacturing process/generation) from the 12V lines (oddly enough, not the 5V lines) and in many cases, use three-phase bucking setups. The isolation, I believe, is for noise purposes, not only for other chipsets on the motherboard but to shield each bucking phase from another - these things have to be very efficient - if phase noise gets to the wrong places in a 40-75A output supply to the processor then you get a lot of heat where it shouldn't be.
     
  15. AlenZGB

    AlenZGB

    170
    4
    Feb 19, 2014
    Looks like ill have to use booster from Ebay.
    Just ordered one. Now the preparations for lab PS case.

    thats some old P4 PSU. nothing special about it. Thats why i want it be gone and serve another purpose :D

    @(*steve*)
    Guess its harder in practice, seen that in my hot air station PCB repair :D
    Kaboom style. i think ill look into it soon :D
     
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