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Seperate 12V rails

Discussion in 'Power Supplies' started by Habakkuk, Apr 12, 2018.

  1. Habakkuk

    Hitman

    Joined: Feb 7, 2017

    Posts: 843

    I'm looking for a 500W+ PSU with separate 12V rails - pref. semi-modular.

    Nice to have, not essential - any with optional fan control below 50% load?

    Thanks!
     
    Last edited: Apr 12, 2018
  2. EsaT

    Mobster

    Joined: Jun 6, 2008

    Posts: 3,657

    Location: Finland

    There are no real separate rails, only current limited wire groups.
    And only thing they achieve for normal users is more trouble in balancing load between them.

    Also there are no load percentage based fan controls, they work based on PSU's temperature.
    Anything else would be bad design seriously risking PSU's endurance if in warmer environment.


    There's semi-modular Antec Earthwatts Gold Pro, but fully modular Seasonic Focus Plus has been even cheaper in discounts.
    Antec has same insides, with difference being in cables and Antec giving 7 (vs 10) year warranty.
     
  3. Habakkuk

    Hitman

    Joined: Feb 7, 2017

    Posts: 843

    The Corsair AX series do - they have a hybrid mode to turn the fan off at low loads.

    How do current-limited wire groups differ from separate rails?
     
  4. EsaT

    Mobster

    Joined: Jun 6, 2008

    Posts: 3,657

    Location: Finland

    Only if PSU's temperature is below certain limit.
    Put it into 50C ambient and I bet fan starts about instantly regardless of "user controls", if not that's very bad design.
    That's the amount of fan control every credible PSU would give user.
    (looks like Antec Earthwatts Gold Pro lost that)

    Go count number of fuses in fuse box.
    You wouldn't claim utility company has that many power lines coming into your house, or would you?
    Similarly those "separate" rails are nothing but marketing BS.
    Actual independent 12V sources would have major extra component costs and space requirements.
     
  5. Habakkuk

    Hitman

    Joined: Feb 7, 2017

    Posts: 843

    Good point, and huh - space requirement aside, are there any actual 12V independent rail PSUs?

    That was a really good analogy thanks.
     
  6. EsaT

    Mobster

    Joined: Jun 6, 2008

    Posts: 3,657

    Location: Finland

    Only one or two have had two separate transformer components feeding separate 12V rectifiers and filtering stages.
    But not sure if even those have had actually independent primary switchers with separate controls.
    It was all marketing BS having roots in Intel once using 240VA (20A at 12V) max output per rail limit in their PSU specs.
    http://www.hardwaresecrets.com/everything-you-need-to-know-about-power-supplies/12/
    Instead of PSU brands admitting, that they have current limited wire groups and that user needs to distribute heavy loads between them (just like you can't pull power allowed by main fuse from sockets behind single fuse) they basically decided to lie.

    Intel ditched that requirement for something like dozen years ago and PSUs with higher power single rail are simply classified as Level 6 devices in UL certification.
    Many better PSUs like Seasonics had those current limits printed on sticker just for show:
    http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=3
    There were lots of such PSUs identifiable from that LEVEL 6 text below UL's logo, which looks like horizontally mirrored LR.
     
  7. LuckyBenski

    Gangster

    Joined: Dec 28, 2017

    Posts: 238

    Location: London

    A pertinent question would be, what do you need separate rails for? Ultimately it's safer and easier to have one rail as you only need to stick below its current limit. Multiple rails, as mentioned, require planning of loads to keep them balanced.
     
  8. Habakkuk

    Hitman

    Joined: Feb 7, 2017

    Posts: 843

    Oh - 3D printer, it's easier to have the extruder and stepper drivers on separate rails so there's not current drops when they're intermittently moving.

    The PSU it came with is a no-name ATX one I don't trust.
     
  9. EsaT

    Mobster

    Joined: Jun 6, 2008

    Posts: 3,657

    Location: Finland

    Artificially current limited wire groups won't make any difference to that.
    Just like that power line coming to house has same "voltage regulation" regardless through which fuses you're drawing that current.

    After that difference is made by if current is distributed to many enough wires.
    Same current through higher resistance of fewer wires increases voltage loss.
    With that "multi rail" current measuring done by using low resistance resistors in fact causing little bit extra voltage loss.

    And those old "multi" rail craps are anyway worser in voltage regulation compared to modern PSUs.
    Especially Seasonic has been pulling some crazy voltage regulation numbers for few years.