Will a 550W PSU be good enough?

rc1974

I asked a question a while back about SLI PSU's. Now, I am wondering if a 550W PSU will be good enough. Mostly I am worried about using an SLI setup with dual 7900GTX cards. I'd get one first, then a second one a few months down the road. Would a 550W PSU be enough to handle two of these cards?

As for the computer setup, I would be getting an A64 X2 4200+ (socket 939 so I can recycle the RAM), the mainboard (Epox or DFI- used these consistently with few problems), the 7900GTX's mentioned before, as well as one 250GB HDD (ATA133), a SATA 200GB HDD, a DVD burner, a TV tuner/PVR card, and an SB XFi sound card.

I'd also like recommendation for PSU's. Nothing over $150, please as I'd like to keep the initial cost of the setup under $1200 with one video card.

madmat

Personally I'd go with a quad rail of at least 700W. The Fortron 700W is a good choice although it's a bit over budget or the Thermaltake toughpower 700W would be another decent PSU.

Mt_Goat

I would certainly go with the 700W Fortron madmat linked to. It will give enough power and is a good solid PSU with an >85 efficency rating. As for motherboard I would go with DFI if you really know your stuff as the BIOS is really extensive. Or go with an Asus if you want to keep it simpler. Both make very stable and reliable boards with good MOSFET cooling, which the Epox boards don't have.

muddocktor

What madmat posted is very true, if you plan to go SLI down the road. Better to bite the bullet now and get a quality psu of no less than 600-700 watts now, with a lot of amps available on the 12v rails, since those SLI/Crossfire setups are so power hungry. Also, you just might consider the new 7950GX2 vid cards instead, since you get 2 gpu's that take up only 1-X16 pci-e slot, fit in the same area as a GTX and are priced just a little higher than the 7900GTX. Hardocp did a recent review of them and they were even able to get quad SLI working with a few games using 2 of those vid cards. On the few games that it worked on, quad SLI waxed everything around. And even though quad SLI isn't presently working with a bunch of games, I look for that to change with future driver releases too.

madmat

With dual rail PSUs, sadly, the mfg's tie the 12V2 rail to the CPU and the CPU only and the 12V1 rail is left for everything to take up the slack. There are a few exceptions, the Ultra X-Finity 500W w/APFC puts a PCI-e slot on 12V2 and on 12V1 so you've got the load spread around. With the new "gaming" quad rail PSUs they're spreading the load around. Generally 12V1 goes to the mobo and drives, 12V2 goes to the CPU and 12V3 and 4 are powering the PCI-e cards so this stops the cards from getting starved.

A 7900GTX draws ~7A and an OC'ed dual core can draw ~9A so spreading the load over more rails really helps.

rc1974

Thanks for the advice.

I usually do a simple upgrade every year, but this time, due to video cards going PCI-E, I am having to upgrade my entire computer (6800GT to 7800GS isn't all that much of an upgrade). I've been looking into the 7950GX2, being that the idea of having future quad SLI sounds exciting. If that PSU is what you recommend, then that is what I will probably get.

As for the mainboard, I'll probably go with DFI. I've been using a DFI board for the last 2 years. I've used Epox boards before that, since at least 1998. They also have not given me any problems. Asus on the other hand, I have not had good luck with; the reason I went with Epox in 1998.

I really only play a few games, but I want them to run well. I'm a casual gamer that is not satisfied with mediocre performance.

The sad thing is when I get around to finally thinking I can do this thing, then something comes up and I have to use the money for something else.

??? would this recommended PSU work ok with a 7950GX2?

Leonardo

That 700W Fortron that they recommended would work with the 7950s.

Take a look at this PSU review. Although they don't test many of the PSUs that would be good candidates for your proposed system, the review is nonetheless instructive and covers many of the issues that need to be considered when selecting a PSU for a high performance gaming rig.