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assistance with modifying pc power supply

Discussion in 'Power Electronics' started by lewisdw, Dec 7, 2012.

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  1. lewisdw

    lewisdw

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    Dec 7, 2012
    Another newbie here. The power supply for my tv went out, so I thought I would use a pc power supply I have. It's a Dell HP-U280EF3, 280W power supply. The tv power supply has a 4 pin cable with 2 24V 6A pins and 1 gnd and 1 12V 3A pin. I planned to use the -12V and +12V from the pc power supply for the +24V and another +12V feed for the +12V. The Dell power supply outputs +5V/20A and +12V/18A and -12V/0.3A.

    I have it all wired and it works with no load, but as soon as I connect the TV, the power supply shuts off. I assume this power supply has some logic that checks for overvoltage and shuts off.

    Can someone tell me what to look for (relay or transistor that can be bypassed to "trick" it into running)? Not sure where I could find schematics for this.

    Thanks,

    wayne
     
  2. BobK

    BobK

    7,682
    1,688
    Jan 5, 2010
    That cannot possibly work. How did you wire it????? What was wired to gnd? The -12V I presume? Then how could it be that one of the 12V lines would supply 24V and the other one only 12V?

    Also the -12V can only supply 0.3A, so how do you expect to get 6A out of it?

    You are lucky the power supply shut off, hopefully before it damaged the TV.

    Bob
     
  3. Rleo6965

    Rleo6965

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    9
    Jan 22, 2012
    Luckily you did not use the +5V dc output. PC power supply shutdown itself if +5 connector have no load.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    As BobK has pointed out, you can't connect the TV between the +12V and -12V outputs because the -12V output can't supply much current at all.

    You can use the +12V outputs from two power supplies, connected in series, IF at least one of the power supplies doesn't have its 0V output rail connected to mains earth. If they both do, then connecting the +12V output of one power supply to the 0V rail from the other power supply will short out the first power supply.

    It's possible to modify PC power supplies by rewinding the transformer and replacing various components, to give different output voltages, but this is definitely not a project for a electronics newbie.

    Also you might be able to find a 12V-to-24V voltage converter that can handle 6A output. Have a look on eBay. Although this won't be much cheaper than a new 24V mains-powered power supply.
     
  5. davenn

    davenn Moderator

    13,838
    1,952
    Sep 5, 2009
    The PC -12V rail only has 300mA current capability
    Because of that, you cant use this rail as part of your 24V supply

    Dave
     
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