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using external power supply for graphics card

Discussion in 'Cases, Modding & Electronics' started by Geofrancis, Oct 10, 2009.

  1. Geofrancis

    Geofrancis

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    my computer only has a 200w power supply and i want to run a hd4850 graphics card in it.

    now i have a 120w 12v power brick spare now can i use it to power the graphics card? i was going to hook the 120w power supply up to the pci-e power connection on the graphics card.

    my main worry are that the slight voltage differences between the two power supplies will damage the graphics card internaly.

    and will the graphics card keep running even after i power the system down because it still has power?
     
  2. I see SPY!

    I see SPY! New Member

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    Okay, first of all, do you know exactly what you are planning to do? Because that does not seem very safe AT ALL. You don't wanna risk frying your machine, do you?

    The only other thing I can think of is using some software like Rivatuner or Ati Tray Tools to heavily undervolt and underclock the card so that the power supply can feed it, but even then I don't think those 200W will be enough...
     
  3. Geofrancis

    Geofrancis

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    like i said i want to run a external 12v power supply into the pci-e power socket on the graphics card to take the load off the internal power supply.

    i know there is graphics card power supplys out there but i already have this 120w psu here so i want to use it.
     
  4. Reventon

    Reventon New Member

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    I'd just get a new PSU. Sounds dangerous.
     
  5. InTeL-iNsIdE Guest

    is it specifically an external psu for graphics cards or is it an old 120w psu ? does it have pcie i have never seen a 120 w with pcie
     
  6. Geofrancis

    Geofrancis

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    its a 120w 12v power brick that i was using for an itx pico psu.

    i was going to make an adapter so i could plug the psu into the graphics card pci-e socket.

    the computer its being installed in has a 200w propriaty power supply that i cannot upgrade so a second power supply is my only option
     
  7. pantherx12

    pantherx12 New Member

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    Why can't you upgrade it? is it rivited to the case?

    Also you would need to do more then create an adapter, you would have to fiddle with the inside of the PSU itself to make sure its the right voltage etc and it doesn't send to much power to the card etc etc.
     
  8. Geofrancis

    Geofrancis

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    the 120w power supply has only a 12v output. the graphics card pci-e socket only takes 12v i dont see the problem with it.

    the power supply has a different shape to normal atx or micro atx power supplies or i would have upgraded it already.
     
  9. mikek75

    mikek75 New Member

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    It should be possible, however, that 120w PSU would barely supply enough power for the card under load.

    This sounds like a blatant advert but I've got a spare Thermaltake GPU PSU, 250w and 25A would be a much better solution. £25 plus however much it would cost to send.
     
  10. pantherx12

    pantherx12 New Member

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    Why do you bother keeping the case? ha ha
     
  11. Geofrancis

    Geofrancis

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    i found a site that looked at the distribution of power into a graphics card from the pcie slot and the pci-e power cable and a hd4850 takes about 55w from the slot and about 55w from the pci-e power socket so im pretty sure that the power supply will be sufficient.

    my main questions are will the graphics card be ok with the 12v power remaining on after the main power supply is turned off? and will the graphics card continue to use power .
     
  12. sneekypeet

    sneekypeet Unpaid Babysitter Staff Member

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    there is a way to link PSU's together to turn on and off at the same time. I would be more worried if the 120W "brick" had the amperage to push said card, not the wattage.
     
  13. mikek75

    mikek75 New Member

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    Yeah, but your 200w PSU is already running hard running the rest of the rig (CPU, Mobo, HDDs, Fans), its not really designed to run discrete graphics. You have to buy an adapter to couple the PSU's anyway. Then it would shut down with the main PSU (in the same way as the GPU supply)

    Tell you what, in the interest of helping a TPUer out, you can have the GPU PSU for £20 + postage. I guarantee it will be a much nicer solution than the ghetto mod you are proposing!
     
  14. Arrakis+9

    Arrakis+9

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    if you want to think about getting one of those thermaltake external psu's i have one and would be willing to sell it on the cheap
     
  15. pantherx12

    pantherx12 New Member

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    I'd say buy a new case, ebuyer do cheap ones that are potentially good with some light modding, then buy a new PSU and run what ever hardware you like!

    Shameless plug, I'm selling a PSU so if you do go down that route PM me for details etc.
     
  16. Geofrancis

    Geofrancis

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    i have seen the vga power supplies thats why i know it can be done. i might use my 120w picopsu to power the graphics card and run a wire from the psu_on pin on the atx plug on the motherboard into the pico psu so that they both power on and off together.

    changing the case or stock power supply is out of the question as i have invested to much time and money in it getting it to where it is and i like a challenge.

    this is the case in question its a morex 669 itx case modified to take a 5x sata hard drive rack
    [​IMG]

    there is only about 7cm above the motherboard and between the back of the rack and the back of the case. there isnt even enough space for the hd 4850 in the pci-e slot so i have had to buy a ribbon pci-e riser and move the card one slot over so i could fit.

    i will take some more pics of the internals soon

    this is the power supply the case takes http://www.itx-warehouse.co.uk/Product.aspx?ProductID=435
    i have seen them up to 220w but thats still no where near enough
     
    Last edited: Oct 11, 2009
  17. _Zod_ New Member

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    Assuming it is 55 Watts at 12v draw at the pcie, that is only about 4.6 amps. So long as that 120 watt supply can deliver I would say a minimum of 10 amps on the 12v rail you'll be fine. I would definitely tap into the signal wire on the 24 pin for the motherboard so both supplies turn on and off together.
     
  18. Geofrancis

    Geofrancis

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    this is the insides of the computer im upgrading

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    i based the project on project udat that i seen here machie.org http://www.mashie.org/casemods/udat1.html

    exept instead of using a via board i used an intel atom 330itx board then i upgraded to a hp 630i dtx + e2180 then to my J&W itx 780g itx board. the next step is to upgrade the graphics card to the hd4850.
     
  19. 3volvedcombat

    3volvedcombat New Member

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    HD 4850 is not an option then T_T. Go for a smaller card like one of evgas no pci-E 6 pin power free 9800gt cards and just turn the key and hope the power supply dosnt xplode. all that for a 200watt powersupply...... Im despreat sometimes, i ran a gtx 260 and a 8800gt on a 500 watt psu with a overclocked 4.2Ghz e5200 and ram. But 200 watts, all the hardrive, and even undervolted hardware aint going to do much, for another max 75 watts i belive idk though of power that would be needed for a 9800gt card because the slot puts 75 watts max output.

    Check out on it though.
    http://www.newegg.com/Product/Product.aspx?Item=N82E16814133279

    http://www.newegg.com/Product/Product.aspx?Item=N82E16814162032

    http://www.newegg.com/Product/Product.aspx?Item=N82E16814500115

    they get all there moneyz from te pci-e slot not having to get moneys from an 6 pin express connector being more of a power hog :).:toast:
     
  20. TheMailMan78

    TheMailMan78 Big Member

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    Subscribed. I must see how this is going to turn out. :laugh:

    I predict some kinda history repeating itself...... Chicago fire anyone?

    [​IMG]
     
  21. Geofrancis

    Geofrancis

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    the 4850 is going into the computer im just trying to figure out how to do it.

    i already sold the 4850 and wanted to buy a hd 4670 but it got returned so now i have the challenge of fitting it into the case and powering it.

    so stop telling me to get a new card or case or power supply or that it cant be done.

    it can be done i just done know how yet lol


    the pci-e riser ribbon cable has already been ordered and i have the 120w psu already waiting so its just a matter of time
     
  22. 3volvedcombat

    3volvedcombat New Member

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  23. MN12BIRD

    MN12BIRD

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    Do you know for certain that this PSU is going to be well regulated under a high load??
     
  24. IINexusII

    IINexusII

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    then i wish good luck
     
  25. Geofrancis

    Geofrancis

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    i have used the 120w psu along with a pico psu to power an atom 330 board along with 4 hard drives without a problem so im pretty sure that it will work ok with a decent load on it
     

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