Using a second power supply to power a GPU

Hi,

Not sure if this is the right forum -- but I'll give this ago.

I want to try to set up a GPU based computing platform try tinker with OpenCL -- a programming system that allows you to send computationally intensive tasks to a GPU.

I have an HP Proliant DL 585 g2 machine ... sadly as I found out it does not have any Molex or other power connections available -- it was designed for cable less operation. And, I was stupid enough not to do enough research and know that GPUs require additional power as they are very power hungry.

I next tried to feed the GPUs using an external PSU hotwired to turn turn on ... I couldn't get it to work though I didn't get the error from GPUs that the power is unhooked.

I didn't ground the power supply to the Proliant -- I figured since they share the same AC power source they're probably grounded.

Any advise?

Thanks.
13 answers Last reply
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  1. Sounds like a recipe for trouble.
  2. phensen said:
    Sounds like a recipe for trouble.


    Really?

    I've seen several articles that seem to combine existing PSUs in serial and parallel but have not found anything that addresses using an external PSU to power devices.

    Thanks.
  3. Sorry for being glib. It sounds like you know power since you've mentioned grounding and parallel and series circuits.

    They do make dedicated GPU power supplies to use in addition to a standard PSU, but they've never been very widely adopted...and it sounds like you're aiming at a homebrew solution using parts you have on hand.

    Here's an article that covers a specific configuration: http://www.hardocp.com/article/2011/01/24/epower_juice_box_450w_auxiliary_power_supply_review/

    I wish you the best in this adventure.
  4. Hi,

    Thanks for the warning -- any insight into why it is a bad idea would really be helpful:

    I have two Radeon HD 4850 that I plan on hooking using a CrossFire Cable.

    Thanks.
  5. It complicates PSU mounting and grounding. It is more complex than a single PSU solution.

    Most of the time people try to make their own startup cables, and in general, they over estimate their soldering skills.

    Generaly they also try to use cheap, generic power supplies.
  6. memmakersorg said:
    Hi,

    Not sure if this is the right forum -- but I'll give this ago.

    I want to try to set up a GPU based computing platform try tinker with OpenCL -- a programming system that allows you to send computationally intensive tasks to a GPU.

    I have an HP Proliant DL 585 g2 machine ... sadly as I found out it does not have any Molex or other power connections available -- it was designed for cable less operation. And, I was stupid enough not to do enough research and know that GPUs require additional power as they are very power hungry.

    I next tried to feed the GPUs using an external PSU hotwired to turn turn on ... I couldn't get it to work though I didn't get the error from GPUs that the power is unhooked.

    I didn't ground the power supply to the Proliant -- I figured since they share the same AC power source they're probably grounded.

    Any advise?

    Thanks.


    How sure are you the "hotwiring" actually turned it on? Also, I don't know, but I would be worried about the timing of the power-ons. It could be that the GPU wants to see idle voltage for a while before it gets the big 12. Turn the second supply on only after the first is up?

    I don't see any other problem with your setup. You are probably right about the grounding, but I would ground the second supply to the case just on general principles.
  7. Thanks for the replies -- I'll try to test these things out today.

    I am using a 250W PSU to drive my GPU -- could that be the problem.
  8. Guys,

    Just as an update -- I was able to the GPU using the external PSU method. As a previous poster has indicated my hot wiring was starting the Fan but not the power I think ...

    I finally got it working for one power cycle -- will test it more extensively today.

    Thanks all for your inputs.
  9. memmakersorg said:
    Guys,

    Just as an update -- I was able to the GPU using the external PSU method. As a previous poster has indicated my hot wiring was starting the Fan but not the power I think ...

    I finally got it working for one power cycle -- will test it more extensively today.

    Thanks all for your inputs.



    Hi memmakerso,

    Are you still using this setup? how is it going - any trouble?

    I have exactly the same problem: GPU(nvidia Quadro 4000) on a server machine with no power cords (IBM system X).

    Are you "hotwiring" the 20 pin (green+black) from the second spu - you said this only turns on the fan but not the power; Did you find a proper method to make it work?

    Thanks,
    I am quite anxious on testing my server/workstation, on the other hand i am afraid not to fry anything - quadro 4000 isn't exactly cheap... :)
  10. Hi there,

    The setup seems to be working ... I'm using my rig for GPU computation ... I have 2 cards so I have hot wired 2 external power supplies acquired from craigslist.

    Now I have not gotten enough hours to be able to say if the rig is stable or whether it will burn anything out :-(

    I have the external PSU's permanently hot wired. The and the server are plugged into an extension cord which I use to switch power on and off.

    Thanks,

    MM.

    cristicraciun said:
    Hi memmakerso,

    Are you still using this setup? how is it going - any trouble?

    I have exactly the same problem: GPU(nvidia Quadro 4000) on a server machine with no power cords (IBM system X).

    Are you "hotwiring" the 20 pin (green+black) from the second spu - you said this only turns on the fan but not the power; Did you find a proper method to make it work?

    Thanks,
    I am quite anxious on testing my server/workstation, on the other hand i am afraid not to fry anything - quadro 4000 isn't exactly cheap... :)
  11. I hate to revive an old thread, but I've been doing this for about 8 years with no issues. I was running dual peltiers with 3 water coolers and a phase exchange cooler on my system. I needed 1600 watts basically. If you look at frozencpu.com they sell 12volt relays. They have power in and a set of normally open contacts which close once 12v is applied to the power sensing end. All you have to do is connect a molex female to the power in and take the greeen and black that you would normally jump together to get the bubbles out of your water cooling rig and attach them to the normally open contacts. I'm using an enermax galaxy 850 for my main system right now with a gtx560 and then using a thermaltake 550 to power an 8800gts for physx and the system fans. Works great and you dont have to worry about mixing power from the two psu's or grounds.
    This time around though, I did notice that even with the power off on the second psu, and completely unplugged except for the pcix cable to the second card, the fan in the external psu continues to spin. That indicates that some power is feeding through the pci x slot and up the cable into the second psu. Scarey thought, but for some reason I have had no issues...and if I turn off the second psu then an alarm sounds indicating loss of power to the second card. Any way you look at it thought, 12vdc feeding into 12vdc is simply like combining rails. So long as you dont cross the polarity you are really just adding amperage to the line.
    Alternatively, and a few bucks cheaper, you can go to the autoparts store and get a cheap 12volt relay. The schematic for the relay will tell you where to apply the 12 volts, use flat crimp connectors to secure your wires and there will be no need for soldering. No need for soldering when using the frozencpu relays either I might add.
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