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Component power use.

Discussion in 'General Hardware' started by JonJ678, 14 Mar 2010.

  1. JonJ678


    Joined: 22 Dec 2008

    Posts: 10,371

    Location: England

    I'm not sure how obsessive I'm going to be with this, depends how interesting the results are I suppose. I've got a DC current clamp, the LH1050. I think it's this thing, but as it's been discontinued it's hard to verify its value. Regardless, it's more than my 6 quid multimeter and I'm in debt to my uni's lab for letting me walk off with one. It should be accurate to 2 or 3% at the values I'm expecting.

    I've also bought some extension cables, as I don't want to strip the braiding from my psu. The plan is to measure the current down the 24 pin, 8 pin and peg cables under various conditions. Tested equipment for obvious reasons is limited to what I have available here.


    i7 920
    Two 8800gt at clockspeeds I can't currently remember
    Gigabyte UD5
    12GB ram
    PC power and cooling psu

    Pinout of an atx cable:
    8 pin and peg cables are much simpler, 12V is yellow and ground is black.
    I'll number the 8 pin atx in much the same way as the pci-e. Stay tuned.

    "Total wattage" includes doubling the 8800GT wattage, as I've got two of them but only one peg extension.

    Idle, cpu at stock
    3.3V 26.4
    5V 29
    12V 40.8
    CPU 26.4
    8800GT 10.8
    Total 144.2

    Cpu load only, cpu at stock
    3.3V 28.7
    5V 40
    12V 45.6
    CPU 62.4
    8800GT 10.8
    Total 198.3

    Turns out my UD5's default settings are unstable. So the rest is being done at my stable 4ghz cpu clock, means comparison between data above and below this comment will be unreliable.

    System idle
    3.3V 27.4
    5V 45
    12V 40.8
    CPU 25.2
    8800GT 10.8
    Total 160

    Both gpu's folding, cpu idle
    3.3V 28.4
    5V 44.5
    12V 94.8
    CPU 26.4
    8800GT 28.8
    Total 251.7

    Both gpu's and cpu folding
    3.3V 27.7
    5V 54.5
    12V 94.8
    CPU 142.8
    8800GT 26.4
    Total 372.6

    Conclusions from this.

    Graphics card draws heavily from the 12V lines in the 24 pin atx connector when under load, cpu load doesn't affect this line.

    Overclocking cpu increases the load on the 5V line. Cpu under load draws heavily through the 8 pin cable. Under full load the system draws 8.5A at 3.3V, 10.9A at 5V. It therefore cannot be run from a pico psu, which was my main interest all along.
    Last edited: 15 Mar 2010