1 PC 2 PSU's, no worries or no way?????

OK, so heres the gist, Can I power my PC through the normal installed PSU and my graphics card through a separate PSU lying on top of my PC.

Heres the detail,
I recently installed a second hand (from a good friend) x850xt gfx card, the system runs fine until I start playing games and then I see stutters and then random lock ups, ctd's, reboots etc. ive played around with various drivers etc, checked connections and ive come down to 2 things, either its because I dont have XP SP2 installed (when I tried SP2 a while back it corrupted my sound :x so I reinstalled xp afresh) or its a power supply problem (see below for PC specs n bits). I dont want to risk putting SP2 on until its a last resort (you never know MS may have fixed the corruption problem with patches, hmmmm) and I dont really want to blow over $100 for a power supply to find it doesnt make a difference. I currently have a 350w PSU (generic, came with a cheap case) thats about 3 years old and I thought that to test the power supply theory I could just borrow another ~300w PSU and plug only the gfx card into it.

Now heres the beef, im worried here about floating commons, PSU's fighting to regulate each other etc as im not sure how much the power from the card input is linked/isolated to/from the power on the mother board through the AGP port.

So before I nuke every circuit and PSU in my PC I just thought id ask a group of like minded people the question of,

1 PC 2 PSU's, no worries or no way?????

any comments or discussions welcome.


P.S. I read the faq and see the bit about diagnosing PS problems and, well, it could be!
9 answers Last reply
More about worries
  1. Hmm. I suppose you could do that - since each connector has its own ground going with it, it has a path back to its own power source...

    I dont' know enough about it to say its safe to combine the power from 2 PSUs without some circuitry to keep out backflow current or not.

    Personally, I'd plug the hard drives, CD Roms, and fans (except PSU fan) into the other PSU. That way you don't need to worry about the above, but you still have removed a couple dozen watts of load from the PSU (depending on the hardware of course).

    In case you dont' know how to fire up a 2nd PSU, Short the green wire on the 20/24 pin mobo connector to any black wire.

  2. thanks for the tip about the green wire, didnt know anything about that. that could have been very frustrating lol...

    I forgot to list my machine specs,
    Sempron 3000 cpu
    2 80gb harddrives
    1 dvd burner
    1 cd burner
    2 normal case fans (not sure on size)
    1 25cm fan in case side panel
    x800xt gfx card
    1gb memory
    Sound Blaster audigy something or other PCI card.
  3. Shorting the green wire will turn the PSU on...lol

    Without doing it you will sit there and lose your mind....lol
  4. Ack, :oops: I meant CPU fan in my original post - keep that fan on the mobo so it can be controlled :)

    LOL - Its kindof hard to connect hte psu fan to the other psu, so I guess that was kindof superfluous... :oops: :oops:
  5. heh, well i didnt pick up on your mistake there but i do appreciate the suggestion, it would be best to have the mobo and the GFX card on the same supply,

    I did a run using only the main psu earlier and disconected all but the main hdd and GFX card but it was still failing, thats why I was looking at the gfx card on a seperate PSU but ill do your idea prob tommorow.

    I was wondering if i should get a second power lead for the existing PSU then i can cut the wire and put my meter inline and measure how much current it is drawing, see if it raises greatly when i start a game up.

    hmm things to play with and ponder on.

  6. AT power supply w00t
  7. what the heck was that ???
  8. That may have been a suggestion to pull out an old AT power supply... no need to short a green wire (there isn't one), because the power switch on an AT PSU is really a power switch... (whereas an ATX PSU needs a signal from the mobo (the green wire) to turn on).

  9. Well i seem to have got the GFX card stable without having to play around with the power supply, thankfully looks like i wont have to blow cash on a new PSU now.

    I put the agp down to 4x and turned off fast write to the AGP port (wanted to adjsut the AGP aperture size but bios doesnt have it) and installed the Omega drivers used ATI Tool to control the card fan to keep the gpu at 60 deg C (it actually could only control it to 62 but that should'nt be a problem at all), and played last night, it still had a couple of small pauses in there but nothing to worry about. At least it looks like i wont have to go and buy a new PSU

    As for porformance hits i dont think there was one but i did turn the settings down when i was having problems so il turn em back up again and start return settings back to the normal values and see if I can work out which particular on made the difference.

    fingers crossed ;)

    thanks for the earlier help, I learned a thing or two from that so it was worth while.
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