Debunking Power Supply Myths
by Christoph Katzer on September 22, 2008 3:00 AM EST- Posted in
- Cases/Cooling/PSUs
Final Thoughts
Building a system these days feels a lot more complex than it was a few years ago. There are many more components in the market, with new ones announced every week, and there's also a lot of overlap. It's nice that some manufacturers are now including advice on power requirements on their products, but that doesn't mean you should take this information at face value. A processor vendor might list a TDP of 150W, but that doesn't necessarily mean that particular processor will actually use 150W. It is more of a rough indication, but at least it's better than nothing.
We have tested processors from AMD and Intel and we have to conclude that the Intel parts are usually far below the listed TDP, where is the AMD parts are sometimes higher. The same applies to graphics cards, but in this case we have a huge difference between the various loading mechanisms. For example, we couldn't reach maximum load on an 8800 Ultra using any current DirectX 10 game, but the Fur benchmark was able to do so. To achieve a similar load, you need to balance frame rates, anti-aliasing, anisotropic filtering, and resolution. High frame rates without AA/AF typically don't put as much of a load on the GPU(s), and likewise high AA/AF settings with low frame rates usually result in lower power consumption. In testing, it seems like maintaining 80 to 100 FPS while increasing AA/AF levels resulted in worst-case power consumption -- though obviously that can vary by application/game.
Something else you need to keep in mind when building a new system is your hard drive power requirements. Most power supplies provide information about their power consumption on the label, although they list current rather than wattage. The power requirements for a hard drive are quite low compared to processors and graphics cards, but remember that hard drives typically need three times as much power during startup as they use during normal use. This only occurs for a split second, so this spike is only visible using an oscilloscope. However, this can cause problems with certain power supplies in combination with larger disk arrays.
Hopefully this article has helped to shed some light on what factors need to be considered when choosing a power supply. Our tests have certainly showed that most components to use nearly as much power as you might think. Look at the tables we've listed on the first page, and then use that information to figure out what sort of power supply you actually need.
Our three sample systems show that few if any people actually need anything more than 850W power supply, especially if you can get an appropriate number of connectors. About the only reason you should consider anything more is if you want to keep your power supply at a lower load, since optimal efficiency and lower noise levels usually come at around half the rated output. Overclockers might also want a bit of extra headroom. Otherwise, there's really no need for a 1000W power supplies, and certainly not those with even higher ratings.
Our power supply reviews include efficiency and noise level charts at various wattage loads. Using these, you can easily compare your own system to see what sort of efficiency and noise you would get. You might be surprised to learn that your intended high-end setup really won't make much use of that spiffy new 1000W PSU; you might be greener than you think!
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Dancer - Thursday, October 22, 2009 - link
On the face of it, this article seems an excellent, well-researched contribution to a highly vexed question. I do have a concern, however: We know that the power output of a PSU drops as it ages. We also know that this drop depends partly on quality and partly due to random chance. If I'm buying a PSU to last 3, 5 or more years, will this seriously affect the capacity of the PSU I should buy for a given machine?internetrush - Saturday, June 6, 2009 - link
Ok, lets low ball it, im running 200w (average) per graphics card, about 50w cpu (core i7) and three hard drives.Lets see
200 x 2
+50 + 50 (motherboard chipset)
+30 Sound card
+10 cd drive
+20 (fans)
During a game, much less a stress test, im lowballing a 600w load on my PSU.
If i had an 800w PSU that would be 80% of its total output, which thereby increases its heat and decreases its life.
When you buy a 1000w PSU, not only are you ensuring that you will never watch your computer go up in smoke (had a friend do that to a 350w on an old P4) but you are also not having to replace it whenever you buy a new processor or add something to your system.
This article is good, however, on a tech website i would expect a bit more consideration for the higher end gamers and common sense.
Common sense says, if you are a higher end system user, you WILL expand said system!
For gods sake! Some cards today use up to 500w power (the 4890X2 and new 295 SuperCard).
As a gamer, id rather have a 2000W PSU that id never have to replace than a 400w that would FRY as soon as i threw on a new video card.
Christoph Katzer - Saturday, August 8, 2009 - link
Sorry for the late reply.You are probably right when you see it from the perspective of a high-end-hardcore-gamer... But do you know how small the percentage of people is who actually own a real high-end system?
JohnMD1022 - Sunday, March 15, 2009 - link
It would be nice if you could periodically update this with newer components.lopri - Tuesday, April 28, 2009 - link
BillyBuerger - Sunday, October 26, 2008 - link
Anyone have any info on that Thermaltake QFan 300? That thing looks great efficiency wise. Not normally a Thermaltake fan. And the fan controller looks like it sucks. Just keep it below 150W... Or fan swap.Christoph Katzer - Thursday, October 30, 2008 - link
I will have a review up soon!Cincybeck - Tuesday, September 30, 2008 - link
Couple of "knowitall" friends were trying to tell me I was going to need a larger power supply when I built my new system. Which in turned incited the Microcenter sales person saying oh yea you're probably going to need that too. I turned around said I estimated these parts to draw at most around 200, 250 watts, and I have a 500W Seasonic M12. Shut him up pretty quickly, but my friends were still pushing it the whole way home. So now if they ever bring it up again I can print this article and shove it in their face. Thanks =D0roo0roo - Sunday, September 28, 2008 - link
i like the graphs:)keep it up!
this is the info we need!
normally the psu market is just lousy because of the lack of any real information.
mark84 - Friday, September 26, 2008 - link
For those quoting that old link for the AtomicMPC graphics card power thread, the new/current one is being maintained here http://forums.atomicmpc.com.au/index.php?showtopic...">http://forums.atomicmpc.com.au/index.php?showtopic...