Computer PSU's in series

Discussion in 'The Projects Forum' started by magnet18, Mar 16, 2011.

  1. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Hey, is it possible to wire two ATX power supplies or general computer power supply uinits in series to create a 24V source with low electrical noise and capable of providing ≈ 4A?

    I know they have a -12V line but it isn't rated for the current. I also know these thigs are really complicated and I wasnt sure if it would be as simple as wiring batteries in series. I can do everything necessary to make it easy to use, I already have one set up as a benchtop supply, but other than what the wires colors mean (purple=standby +5V _ green=power on, input _ gray=power on, output _ blue=-12V _ white=-5V _ black=ground _ orange=+3.3V _ red=+5V _ yellow=+12V), but if both the ground lines are mains-grounded... I become confused.

    Any help's appreciated, thanks :)
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You can't do it safely, because the supply grounds (black wires) are connected to earth ground via the power plug. If you attempted to "float" one supply (not connected to earth ground) and there was an internal breakdown/failure, you could wind up with mains power on the chassis of the "floated" unit, which would be quite hazardous.

    MPJA has a 24v 100W 4.5A switching supply for $32.80+shipping:
    http://www.mpja.com/prodinfo.asp?number=16015+PS

    BG Micro has a 24v 6.5A switching supply on sale for $15.40, but it uses Molex connectors of a type I don't recall seeing. If you can't get the correct connectors, you'd probably have to unsolder the Molex connectors and hard-wire it. The documentation available for it only covers the terminal strip type connections.
     
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  3. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Thats what I was afraid of. :(
    Thanks for the links, but since it only needs powered for a few seconds at a time (plasma speaker), I'll probably just stick with some sealed lead-acid batteries in the garage.
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,094
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    Batteries are simple enough.

    It would also be possible to devise a scheme whereby a large capacitor is charged in parallel to your supply and then switched to be added in series with it, giving you a brief burst of voltage above your supply capability, dropping from 2X to 0X as the cap discharges. It goes to zero because the cap cannot pass a DC current. But the switching scheme can place it back in parallel for recharging once it has fallen to whatever level you want to switch on. The current while discharging would still be limited to whatever your supply is capable of.
     
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  5. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    What's the maximum speed that can be done at?
    Is it possible to set up a switcher to switch rapidly enough to provide an apparent DC voltage if it's smoothed out?
    Maybe if there were 2 caps, one charging while the other discharges?

    Seconds might have been a bit of an understatement for the time this needs to be on, maybe a minuet or so at a go. (I'll probably use batteries, I'm just curious now)
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Last couple I've bought had a wiring harness included. I don't know if this is universal, but the odds are good.
     
  7. magnet18

    Thread Starter Senior Member

    Dec 22, 2010
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    Would it be safe to wire one 12V battery in series with the ATX?

    *unneccessary commment deleted
     
    Last edited: Mar 18, 2011
  8. SgtWookie

    Expert

    Jul 17, 2007
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    1,728
    You could wire a 12v battery in series with the ATX PSU +12v output safely.
     
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