Hi. At a website where I’m doing some computer shopping, it says a 500watt power supply is recommended for any SLI setup. Of course, this company just happens to have a few of these PSUs handy for an extra fifty bucks.
I was thinking about either a 7600GT SLI or 7900GT SLI setup. My question is, am I really going to need a 500 watt power supply for either of these setups? Or can I get away with 420 watts? (350?)
I know it depends on what else is in the system, probably, but what can you say about the probabilities based just on what I’ve said here?
If you’re paying that much money for a computer setup, having a higher wattage PSU than you may absolutely need makes sense. First, a PSU that is having to run at close to its maximum capacity will run hotter and with more wear than one that has some extra room to run. Second, especially if you’re running with more than one hard drive, or plan on upgrading parts in the future, it makes sense to leave some room for upgrade. And finally, if you put out the money for a higher-quality PSU, and a part fries in your computer, your PSU will often sacrifice itself to save your other components, rather than risking having your whole rig go down.
If you want to see how big of a PSU you need (according to the site’s author, at least), this is a calculator which projects PSU needs.
A 7600GT at peak load runs you about 35-40W (link), so two would be 75-80. 7900GTs peak at about 50W (link). Processors at max load will be most likely somewhere between 70-140W, depending. Intels outside of the new Core 2 Duos tend to have higher power demands than AMD processors, though there are probably exceptions. Toss in 10 watts or so per hard drive, stick of ram, optical drive, etc, in the system. There’s no way you need 500W. However, many power supply manufacturers’ specifications are, shall we say, somewhat optimistic. But if you’re getting a good reputable brand of psu, 350-400W are plenty, even with cutting edge power-hungry components. Keep in mind that it’s virtually impossible to actually have ALL your components drawing maximum power simultaneously, outside of running a bunch of benchmark software specifically designed to do exactly that.
if you’re lashing together a thousand bucks or more worth of video cards, why would you even think about cheaping out on the power?
These cards draw amps. *Lots * of them, to the point they can’t even be powered by the PCI Express or AGP bus. They take their power, instead, through drive connectors. I’m looking at one right now that takes so much juice, it’s actually fed by two drive connectors.
If you’re running SLI or Crossfire, you will want a SLI/Crossfire certified PSU. As Gorsnak said, a lot of PSU vendors are absurdly optimistic with their ratings, and are advertising peak outputs. Reputable companies such as PC Power & Cooling are advertising steady load outputs that will let you run for hours at a time without worrying that the magic blue smoke is going to leak out of anything.
While I agree about not cheaping out on power, it’s important to point out that this doesn’t mean spending more money on a PSU rated at a higher wattage. It means spending more money to get a PSU from a quality manufacturer. Seasonic and Fortron are two names that come to mind, though there are many others. Avoid the cheap generic power supplies that come by default with cheap cases (though some manufacturers do supply decent psus - Antec, for example). But I’d be pretty surprised if you could put together a system using nVidea graphics cards that draws more than 300W at peak load, especially if you’re using a new AMD socket AM2 cpu or Intel Core 2 Duo cpu. Maybe if you build a Pentium D system using dual X1900XTs in a Crossfire setup you might get to 500W. Maybe.
Man, I get a ton of mileage out of this article. Tom’s Hardware did a review of 21 power supplies, testing them against the labeled specs. You can read it yourself to get all the gory details, but Fortron and Verax (which is a relabeled Fortron) both did well, as well as Herolchi. I’d go with a Fortron from Newegg, and use a reliable PSU spec page to determine what size you’ll need. Figure out the most of everything you could ever use with your current motherboard (RAM, CPUs, HDDs, burners, video cards) and spec for that amount – with any luck you’ll be able to carry the PSU into your next case.
Fanboy disclaimer: I’ve bought four Fortron power supplies in a variety of wattages since that article was published, and all of them have handled demanding loads without complaint. Among other challenges I’ve thrown at them are RAIDs, high-end video cards, RAM overvolting, mild overclocking and CPU over- (and under- ) volting, video card overvolting, and large electronics surplus muffin fans that never should have been attached to a PC.
Wattage is important, but not as important as quality and the number and amperage of the 12v rails.
For an SLI setup you want atleast 2 seperate rails rated at 18 to 24 amps. Like evryone else said, don’t skimp on the PSU, specially on power hungry systems.
Another observation:
There are two main reasons to go SLI.
As an upgrade path - buy one high end card now, get the second one a year later in order to keep up with the high end games.
In order to play high end games at high resolutions (1600x1200, 1680x1080, etc and higher).
A 7600 GT SLI setup fulfills none of these. A 7900GT setup will do very good at point number 2. So go with the 7900, or better yet, get the 7900 GTX and buy another one next year, or whenever your next fave game comes out.
I have an observation as well as a confession WRT this thread.
I do computer repair full time for a living…and I buy cheap power supplies. I pay like $18 (inc shipping) a piece for Power Magic 550W supplies that so far I have sold 18 in 10 months (last one I sold was about 2 weeks ago). None of them have inspired a warranty call even through a week long run recently of 110+ temps.
The problems that having an inadequate or bad power supply creates are often subtle and hard to tie back to the PSU. For instance - your video card glitches occasionally… normally think “must be inadequate power”? - no, but that’s often the case. Random crashes. Memory errors.
Most people can get by with a crappy power supply because they don’t stress their systems much, but for a gaming rig, I’d never skimp on the PSU.
Quality is more important than raw wattage ratings. The right amount of amps on each rail, too, is more important than the total power. Do some research into reviews. You’d probably be fine on a 430W power supply (I am) so long as it’s high quality.
There’s little point in spending megabucks on a graphics setup when DX10 cards are just around the corner. Unless someone else is paying, of course. But I agree with the 7900 comments - one of those will likely do you far better for less cost than two 7600s.
Likewise, building any new system right now is sort of foolish; by October AMD and Intel’s prices will both be down significantly. They’ve made the pricing changes for their vendors already, but a second wave of cuts may be coming in October, and the July cuts are already trickling down.
I’m fully aware of the possibilities and test and or swap out PSU’s to see if it fixes a twichy system on a regular basis. Just so far in my experience $100 PSU’s are not worth it. Several of these PSU’s I installed are on gaming machines, including my own SLI setup, no problems so far. I will not say that good PSU does not put out cleaner more stable power, im know they do. However cost to benefit wise, I have been working with computers in some way or another for almost ten years, and I have seen my share of dead $100 power supplies and toasted motherboards with a couple of those. It might be less common, but I personally would rather swap out the occasional $18 failure than pay 5-6 times that for a PSU outside of a mission critical business machine where downtime is costing you money.
I was surprised when I went to install my 6600GT that it needed a 5V power connector (the same ones that plug into the hard drives.) I used a splitter to split an existing connector, but my system ran like crap. The video card was scaling down performance to deal with not getting enough power. I found I had to give it a “pure” 5V connector coming from the power supply, no splits, then it ran fine.
So, if they ask for a 500W power supply they probably have a good reason to say that.
