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
Edit: Christoph's text reflect the range for 90VAC to 230VAC, but my editing made that a little less clear. I've added in "input voltage" comments to clarify things.poohbear - Monday, September 22, 2008 - link
thanks for this article!!! im planning on running 2 8800gt's in SLI on a 80% efficient enermax 420wt psu. it has 29a on the 12v+ line so im confident it can run it. All this BS about needing 500+wts psus is nonsense if you know your cards power needs.bela - Monday, September 22, 2008 - link
Where did you get those power figures? Dream last night or what?This is totally made up bullshit.
The ANTI-AMD war continues @ Anandtech
you compare 2 year old 90nm AMD DC with new 45nm Intel DC, is that a fair peer group?
6000+ 160W load? Even with 90nm this ist ridicoulus, it should be around 110W, a new 65nm 6000+ needs less then 80 Watt, a 65nm 5000+ less then 60W, so talk about making Intel look good.
elaar - Monday, September 22, 2008 - link
bela, you seem to be incredibly rude and have also missed the entire point of the article, if it makes you that annoyed then why not do us all a favour and stop reading articles and commenting in the future.I for one found the article incredibly useful especially when you consider the sheer number of people who go out and buy way too powerful psu's and have no idea what they're doing.
It doesn't matter what processor or graphics cards power stats were listed, they were just there as examples for the article, god knows how you've managed to get so confused with paranoia to believe it was an anti AMD campaign.
Thanks Anandtech for a superb article.
npp - Monday, September 22, 2008 - link
The power draw figures for the X2 6000+ are a bit off-scale (and yes, it is an older 90nm die, apparently), it's a tiny bit, however. You can have a look at the charts here (damn, the stupid link button doesn't work):http://xbitlabs.com/articles/cpu/display/dualcore-...">http://xbitlabs.com/articles/cpu/display/dualcore-...
The system equiped with an X2 6000+ was measured to draw about 304W at full load and 180W at idle. Adding ~25W to that difference makes for ~150 total power consumption, which comes close to what was stated in the article. Just because you thought "it should be around 110W" doesn't make you automaticaly right. Learn living with the truth and stop behaving like a small child.
Furthermore, as it was properly stated, those figures were intended to draw a frame around the best and worst case scenarios, representing some of the CPUs typicaly found in a system today. They weren't meant as a CPU-to-CPU comparison.
That old dark sense of anti-AMD or anti-Intel paranoia continues to be abundant in every discussion nowadays... What a triumph for the PR brainwashers at both camps.
bela - Friday, September 26, 2008 - link
No, they are not of scale, they are bullshit, nothing else but made up numbers.Look at this:
X2 6400+ WITH Voltage Regulator, depending on Board 85,9 or 103,3 Watt
http://ht4u.net/reviews/2008/amd_phenom_leistungsa...">http://ht4u.net/reviews/2008/amd_phenom_leistungsa...
This ist the truth, nothing else
Kiijibari - Monday, September 22, 2008 - link
Could this be a typo ?106W is ok, 160W is a little bit out of the "normal" scale ..
Furthermore .. which 6000+ is it ?
There are 3 different models:
one 90nm "normal" model: 125W 3,0 GHz; 2x1MB L2 (ADX6000IAA6CZ)
one 90nm EE model: 89W 3,0 GHz; 2x1MB L2 (ADA6000IAA6CZ)
one 65nm model: 89W 3,1 GHz; 2x512kB L2 Cache (ADV6000IAA5DO)
cheers
Kiiji
JPForums - Monday, September 22, 2008 - link
This is a curiosity for me as well.I have an A64 X2 6400+ 125W, 3.2GHz, 2x1MB L2 (don't remember the model number off hand) that doesn't seem to require near that power.
The 6400+ is running on an nForce 570SLI with 8Gb (4x2Gb) DDR2-800.
The video card is an 8800GTS 512Mb.
I have 4 HDDs 2 optical drives and 8 fans (7 case + CPU fan) that according to specifications run at 8.6W when at full speed (how I have them while gaming).
If I use the (presumably lower) power ratings used for the 6000+ and the 8800GT, and I exclude the power of usb components and the fan controller/sensor overhead, my total system consumption at load (using the values from the article) is around 450W.
The curiosity is that the same Enermax Pro82+ 385W PSU mentioned in the article has no issue running this system. (Ironically emphasizing the point of the article) Using a basic kill-a-watt meter, I found a power draw of 378.2 was as high as it got during benchmarking, gaming, stressing the system. For reference, I tried 3DMarks 2006/Vantage, Stalker, Crysis, C&C3, and a combination of 2xPrime95 + ATItool's GPU heat up mode (rotating fuzzy block). The ATI tool combo offered the largest power draw in my system. Granted, the kill-a-watt may not be as accurate and I may not have stressed the system as well as in the article, but I suspect the power draw numbers for the 6000+ are lower than the article suggests.
That small inconsistency aside, this was a nice article. I would like to see those power draw blocks that you overlayed on the power efficiency and noise curves included in future PSU reviews. It would be a quick and easy way to let people know how applicable the PSU being reviewed is to them. It would also be interesting to see how high the power draw gets with water cooling systems, case mods (I.E. cold cathodes), and the likes.
Christoph Katzer - Monday, September 22, 2008 - link
My 6000+ was 90nm, yours?Kiijibari - Monday, September 22, 2008 - link
He has a 6400+, that CPU is 90nm only (so far).But he has a AM2 mainboard, maybe you had a AM2+ board, and the onboard VRMs are running badly with a AM2 CPU ?
cheers
Kiiji