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Running grapics card with dedicated PSU

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October 3, 2012 6:44:42 PM

Helllo folks, im in a bit of a bind. I had an older graphics card die out on me. (GTX460) And ive acquired a better one and my power supply is having problems with it. The newer card is a GTX 580 and I know its a power hog but with it in my main system, my 12v rail dropped to about 11.4 volts and system instability ensured. I was wondering what are the risks and dangers of running a dedicated secondary supply to the graphics card alone. I know how to jump another power supply to use it but what would be the best method, dangers of doing this? I cannot afford a newer higher wattage power supply and my current one (Corsair GS 600) Can not do the job on its own. I have an antec 550 watt extra PSU that I have no use for. Would it be safe to run the graphics card off its own supply or not?

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a b ) Power supply
a b U Graphics card
October 3, 2012 7:03:32 PM
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Whether or not it would work depends on how well the 12V-only PSU would cope with having single-rail load and how gracefully it might handle load-sharing.

Possible scenarios:
1- worst case: the 12V-only PSU cannot operate heavy 12V load without any load on 3.3/5V rails, trips an over-voltage protection which activates crowbar circuitry on the 12V, shorts out the 12V rail, the heavy combined current ends up burning PCB traces on the GPU, PSU wires and possibly the PSUs themselves.

2- voltage regulation between PSUs gets messed up due to fluctuations on the 12V rail as both PSUs try to level off, the main PSU's 3.3/5V outputs end up out-of-bounds because of it and you end up with crashes, reboots, etc.

3- everything goes well and it actually works.

Since normal PSUs are not designed for load-sharing, the most likely outcome will be somewhere between #2 and #3.
October 3, 2012 7:17:55 PM

Well thats what I was thinking too but wanted a second opinion. Now if I load up the 5v side of the secondary PSU, will that provide a better result or would the risks be the same. Ive used a secondary PSU in older machines Ive had mainly to run extra HDD's and the like but this is a high current drawing card so it is a bit different and I really don't want to fry this card or my system. Power supply will be hooked up just to the power ports on the card.
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a b ) Power supply
a b U Graphics card
October 3, 2012 9:13:53 PM

Loading the other rails is only necessary if the 12V-only PSU has trouble operating properly when loaded that way. Ex.: if the PSU's control loop tracks 3.3V output which has no load while the 12V rail is heavily loaded, the 12V rail may end up drooping a lot since the 3.3V rail stays topped off at very low PWM duty cycle.
October 22, 2012 11:58:23 PM

Best answer selected by umbre.
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