Debunking Power Supply Myths
by Christoph Katzer on September 22, 2008 3:00 AM EST- Posted in
- Cases/Cooling/PSUs
Connectors and the 12V Rail Issue, Cont'd
As a second example, let's take our high-end system. This requires more power, making it a little more difficult to find an appropriate power supply -- especially if you want to run 3-way SLI. NVIDIA initially only certified 1200W power supplies for that sort of setup, but Corsair was eventually able to receive this certification for a 1000W unit. To run a 3-way SLI setup, we need at least six 6-pin PEG connectors, so let's start by looking at the number of connectors available on our high-end PSUs.
| PSU PEG Connectors | |||
| Manufacturer and Name | # of 6-pin PEG Connectors | # of 6/8-pin PEG Connectors | Total |
| Antec NeoPower Blue | 1 | 1 | 2 |
| Antec Signature | 2 | 2 | 4 |
| Silverstone Decathlon | 4 | 0 | 4 |
| Zalman ZM850HP | 2 | 2 | 4 |
| Enermax Pro82+ | 0 | 4 | 4 |
As you can see, none of the power supplies we listed are able to run more than two GPUs, since none of them have the available six PEG connectors. We still don't recommend 3-way SLI, has the advantages over two-way SLI are sketchy at best. Regular SLI also has the advantage of only requiring four 6-pin PEG connectors even for the highest-end GPUs. All of the listed power supplies can meet this requirement, except for the Antec NeoPower Blue.
For the second 12V rail issue, here's a look at the specific power requirements of our graphics card, the GeForce 8800 Ultra:
| GPU Power Requirements by Connector | |||||
| Vendor and Chip | Through 6-pin Jack |
Through PCI-E Slot |
Total Power | ||
| NVIDIA GeForce 8800 Ultra | 9.4A | 112.8W | 6.1A | 72.2W | 186W |
If you plan to run multiple cards, you can just multiply 186W by the number of cards in the system. We found during testing that the cards don't consume equal amounts of power. The first GPU always uses the same amount of power, whether in a single or SLI configuration. The second and third cards however require much less power, which also means that they are doing less work. In testing a variety of benchmarks and games, we saw that the second and third graphics cards only use 40% to 50% of the power of a single GPU.
One thing is obvious when looking at the power consumption of the single GeForce 8800 Ultra: the maximum power draw is only 15.5A, which you can get from a single 12V rail. Most higher-end power supplies have multiple 12V rails, which should make distributing power to your GPUs even easier. As long as the 24-pin ATX connector and the different 6-pin PEG connectors run on different 12V rails, none of the rails should end up with an excessive load. That takes care of the 300W power requirements mentioned by GPU vendors.
If you take the high-end system (with an optional third graphics card), you are looking at one of the most demanding systems available. Of course, you could always overclock the processor and graphics cards, which might increase power requirements by another 30%, but we'll leave that topic for another day. We were able to run this test system with a normal 850W power supply, and even with a reasonable load the PSU fan didn't make that much noise. Most of the high-end PSUs we've chosen for this article could also run a triple-SLI setup, provided they have sufficient connectors.
At the beginning of the year, we requested a special AnandTech Edition of PC Power & Cooling's Turbo Cool 860W power supply with six PEG connectors, specifically for running a triple-SLI setup. We have been using the power supply since then with three GeForce 8800 Ultra cards, an Intel Core 2 Extreme QX6850 CPU, and 12 Western Digital hard drives without any problems. Clearly, quality of construction and number of connectors are far more important than a silly wattage rating.
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JarredWalton - Monday, September 22, 2008 - link
If you look at all the included components, it should be pretty clear that the latest parts won't be drastically different from the tested components. Sure, 4870 might use 30W more (or 30W less) than the 3870, and the P45 might use +/-10W relative to the P35. Does that really change anything with the information the article conveys? I don't think so. Midrange PCs are still going to use 150-250W for the most part, whether with last year's components or with the latest stuff. If you want to look at the top-end, then GTX 280 will use more power than the listed GPUs, but even then you're not going to break 600W without overclocking.Martimus - Tuesday, September 23, 2008 - link
Thanks. I have since calculated out what is needed for the processor and chipset (for a E8400 and P45 MB) and it came to about 8A. I went on the AMD website to find what the current draw was from the 4870. It doesn't say, but does recommend a 500W PSU. I am a little concerned though, because the EA500 isn't on their approved PSU list from Antec, and I have had issues with their power supplies before, plus they only have 17A available on each rail. that should be fine, but I would like to make sure I am not loading the 12V rail too heavily as well. If those components don't work (those are my plan for the moment), then I can always adjust, but I would like to have that peace of mind before I make the purchases. (the computer is a present, and I bought the Sonata III to save money because I heard good things about the Earthwatts brand, but now I am starting to get worried about this particular model.)Matt Campbell - Monday, September 22, 2008 - link
I would also point out that in addition to all of the data Christoph has pulled together, we have some power consumption numbers on overclocked systems with GTX 280s as well, which seems to be one area people are asking for.4.0 GHz QX9770 with SLI GTX 280s: 579W Max
4.0 GHz QX9650 with Triple 8800 Ultras: 671W Max
JarredWalton - Monday, September 22, 2008 - link
Those figures are power at the outlet, though, right? And they're not tested in the same fashion as what Christoph did. Still, if you max out at 671W at the outlet, even with 88% efficiency you're only using 590W - nowhere near 1200W, which is what NVIDIA certifies for 3-way SLI. Quality over quantity, naturally, but there really aren't many terrible 1000W PSUs out there (which is why they all cost over $200).Torched - Monday, September 22, 2008 - link
For all the hullabaloo about the 12v Rail why nor just recommend a PS that has a single rail. More and more manufacturers are going in that direction anyways since it eliminates the whole power trapping issue.gramboh - Monday, September 22, 2008 - link
Good article. The underlying point is that you do not need 1000-1500W PSUs to run your system like I see many people claiming you do for SLI setups. I see lots of people with 700-800W PSUs with one graphics card. Insane.I've been running a Corsair HX520 (520W) for a year and a half now. My current config is:
Asus P5B-Deluxe (P965) mobo
Q6700 G0 @ 3.3GHz (1.42v actual voltage reported by Speedfan)
4x1GB PC2-6400 DDR2 memory
EVGA GTX280 video card overclocked (675-1350-2422)
3 hard drives (7200.11 1TB + 2x 7200.10 500GB)
1 optical (18x Samsung DVDRW SATA)
3 case fans ~1500rpm + CPU fan 1200rpm
SB X-Fi XtremeGamer audio
Zero issues and I'm sure I have headroom to spare. Some people on forums told me I should upgrade my PSU to at least a 650W Corsair or 750-800 of other brands to run the 6700/GTX280, just goes to show people have fallen for the marketing hype of PSUs.
cesthree - Monday, September 22, 2008 - link
I have had a few different systems in the last 6 months. Using the Zalman MFC-2 I can see the wattage being used in real-time. How accurate it is, I do not know, but it gets me in the ballpark.All systems have had the same 4 WD1600YS HDD, Lite-On DVD burner, 700W OCZ GameXStream PSU, and OCZ DDR3 1333Mhz 2x1 GB RAM. I also run 4 x 120mm fans including the one mounted to my TRUE-120.
Set-ups:
1. EVGA 790i Ultra (JUNK) w/ Q6600 @ 3.2Ghz 1.35VCORE, 1400Mhz FSB, 8800GTS 320MB SLI
Idle Load: 225W, Prime Load: 275W, 3DMARK06: 325W.
Never saw higher than 400-425W during highest loads.
2. DFI X48-T3RS (PWNING 790i ULTRA) w/ Q6600 @ 3.0Ghz 1.32VCORE, 1333Mhz FSB, EVGA 9800GTX
Idle Load: 200W, Prime Load: 250W, 3DMARK06: 290W.
Never saw higher than 350-375W during highest loads.
3. DFI X48-T3RS w/ E8400 @ 3.0Ghz 1.245VCORE, 1333MHZ FSB, EVGA 9800GTX
Idle Load: 175W, Prime Load: 200W, 3DMARK06: 250W.
Never saw higher than 300-325W during highest loads.
BTW, all Watts are averages. Prime Load is averages between blend testing and small FFT's.
I really like the meter on the MFC-2. If it is at all accurate, then it supports the logic that it isn't always necessary to have a 2000KW PSU.
I could see needing a higher wattage, QUALITY PSU, for CF or SLI + the latest GPU'S, non-extreme CPU, with everything OC'd 25-50%, and maybe a single loop WC as well.
Just my 2 cents.
Spacecomber - Monday, September 22, 2008 - link
I was wondering if it might have been helpful to add some comments on the importance (or not) or having 8-pin 12-volt motherboard connectors, instead of the more standard 4-pin motherboard connector. I don't think that this motherboard connector, which I think largely powers the CPU, was given much attention relative to the discussion of the additional 4-pin connector for the main motherboard connector (20 + 4) and the PCI-E power connectors.Overall, this was a very good article. I like how it places technical details about power supplies into a context of everyday use.
CSMR - Monday, September 22, 2008 - link
The power consumption data on page 1 is completely overblown.The tables claim to represent actual power consumption of processors and chipsets but the figures are completely exaggerated.
There are even people who run whole systems on one or two of the chipsets listed on less power than the power the article claims for just the chipset.
Here are actual CPU measurements from behardware and xbitlabs:
http://www.xbitlabs.com/articles/cpu/display/intel...">http://www.xbitlabs.com/articles/cpu/display/intel...
http://www.xbitlabs.com/articles/cpu/display/intel...">http://www.xbitlabs.com/articles/cpu/display/intel...
I haven't seen measurements of chipset power but here is a list of TDPs:
http://www.silentpcreview.com/forums/viewtopic.php...">http://www.silentpcreview.com/forums/viewtopic.php...
Must fix this soon as Anand needs to keep its reputation for good information.
Zoatebix - Monday, September 22, 2008 - link
Seriously. This guy didn't go too far our of his way to make a 30-40 watt system: http://www.silentpcreview.com/forums/viewtopic.php...">http://www.silentpcreview.com/forums/vi...tdays=0&...