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PC power suplay modification

Discussion in 'General Electronics' started by Tomislav Hajak, Nov 17, 2003.

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  1. Hi!
    I would like to know is it possible to modify pc power suplay so that I can
    change voltage with pot? I hope you understand what i want, some kind of
    adjustable voltage regulator with potentiometer. Anyone done something like
    that? Any links?
  2. Tim Auton

    Tim Auton Guest

    It depends on the design of the power supply whether it's practical
    but it's probably not impossible. I'm not sure how much variation you
    want but ATX PSUs are designed with +3.3, +5, +12, -5 and -12V
    outputs in mind so even if you could alter the output more than a
    fraction of a volt it wouldn't be a good idea.
    Try a search for "psu voltage mod", overclockers do this kind of thing
    quite a lot.

    is one example.

  3. Jeff

    Jeff Guest

    I have made the 3.3 V line adjustable on a ATX supply (it went something
    like 2.1 to 4.5V)

    The 5V line can also be modified to differnt voltages by changing the
    feedback resistor (to a pot in your case). Keep in mind all the other
    voltages are a ratio of the 5 V line, so you change it, you change them all.
    Also keep in mind the maximum votages allowed on the capacitors, the power
    good circcit, and power dissipation in various parts if you go much above

    There is one link on the web where someone made a 13.8V power suppy out of
    an old PC supply. He did make one mistake in assuming the transformer in the
    supply was wound with wire, however he did get good results.
  4. Possible? Maybe. Desirable? Probably not.

    If you're serious about needing an adjustable bench supply, my
    advice would be to build one out of something like the 'Radio Amateur's
    Handbook' or buy one as surplus.

    Trying to modify something like a PC's power supply, which was
    designed to provide fixed voltages and currents from the ground up,
    especially considering the utter lack of schematics for most of them,
    would not be my first choice.

    Dr. Anton Squeegee, Director, Dutch Surrealist Plumbing Institute
    (Known to some as Bruce Lane, KC7GR)
    kyrrin a/t bluefeathertech d-o=t c&o&m
    Motorola Radio Programming & Service Available -
    "Quando Omni Flunkus Moritati" (Red Green)
  5. Nico Coesel

    Nico Coesel Guest

    Could you elaborate a bit more? I've made a similar modification to
    get +/- 25V (50V in total) from a old PC PSU by connecting several
    windings in series.
  6. Ben Pope

    Ben Pope Guest

    What for?

    The 12V and 5V lines are generally regulated with a chip and so increasing
    the voltage may be hard.

  7. Lane Lewis

    Lane Lewis Guest
  8. Nico Coesel

    Nico Coesel Guest

  9. Joel Kolstad

    Joel Kolstad Guest

    What makes you say that? Antec makes decent power supplies, and all they're
    advertising is the ability to tweak the output voltage -- something the
    overclockers like to do to squeeze some more performance out of their CPUs.
  10. Nico Coesel

    Nico Coesel Guest

    I quote:
    "Power is truly addictive"
    "whopping 550 watts"
    "impressive degree of control"
    "Gold plated connectors."
    "Voltage Feedback to maintain accurate voltage to all components: adds
    stability to your system"

    Sorry, but these are the labels on a bogus product. If the PMPO rating
    was still being used, they would rate it at 100kW PMPO.

    The specs aren't that specteculair either; PFC is not mentioned, the
    efficiency is quite poor, load regulation is just within limits, it's
    operating temperature is limited to 50 degrees Celcius (which is
    severly low when taking into account that it has to cool itself with
    an airflow in which 550 Watts got dissipated already).
    I suspect this is an ordinary PC PSU (given the fact that it still has
    a combined maximum output which implies one switcher / output
  11. Ken Taylor

    Ken Taylor Guest

    Marketing spiel.
    550W is 'whopping' (at least in marketing terms) in PC supplies.
    Given the normal degree of control (~0) this is at least pretty good.
    Normal for connectors of any worth.
    Marketing blah blah's, but true.
    Without a CE certification, its PFC is probably shit, but then again what's
    new? What's your beef with the power dissipation? At worst efficiency
    quoted, it's dissipating about 250W, and it's fans will be drawing in
    external air so the other 550W is irrelevant.

    The product may not be up to your exacting standards, but it's harsh in the
    extreme to label it 'bogus' just because the marketers are at work (as they
    always are).

  12. Tim Auton

    Tim Auton Guest

    Relative to what other PC power supplies?
    The inefficiency of the power supply (too drunk to look it up, let's
    say 75% efficiency) means that 412W was dissipated before it got to
    the PSU, not 550W. PC PSU wattage is rated by consumption, not output.
    It's the biggest number, that's marketing for you. Even that is making
    the ridiculous assumption that the user was following the minimum ATX
    spec and had only the PSU removing air from the case. The combination
    of a user who actually uses the full 412W in their machine and has no
    additional ventilation is so spectacularly improbable that it is
    irrelevant. If the PSU is all you have removing hot air from your
    components and they are using 412W you will have other problems
    (overheating CPU, RAM and GFX card) well before the PSU becomes a
    It's a higher quality PSU than most of the crap out there. If you want
    to compare PC PSUs the compare maximum current on the lines you are
    interested in, from that you can work out the total output. I think
    you'll find Antec are up there with the best in that market. PC PSUs
    are cheap, mass produced items, not laboratory quality devices.

    Show me a PC PSU substantially better than an Antec. If you can't then
    you have found a niche in the market - go and make some and sell them.
    If you're right you'll be rich.

  13. mike

    mike Guest

    YOu'd be a lot better of to start with a real adjustable, regulated,
    metered supply like one of these:

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