Using a AXi Series PSU and Corsair Link's "power" tab with different configurations to determine power usage during different tasks
By Jonny Gerow posted May 31st 2013
I was curious as to how much power my gaming PC uses with one, two and three graphics cards installed and how that compared to using the integrated graphics of my Intel® Core™ i5 CPU. Corsair Link and my Corsair AX Series Digital ATX PSU helped me determine that! In this blog entry, I show how much power my PC uses with the different configurations.
Right now I have a Core i5-3570K running at 3.4GHz and three Gigabyte GTX670 2GB cards each running at 980MHz.
Currently, I'm just sitting here typing this while listening to music streaming on Pandora. Not a lot going on, so I'm seeing what sums up to a whole lot of nothing going on within Corsair Link. I'm pulling 224.9W from the wall, which is still a lot... but that's primarily because I'm keeping three graphics cards powered even though I'm not using them. Spoiler: We'll see that number lower as I take cards out of the system, even sitting here doing a whole lot of nothing.
All of the PCIe power connectors are at zero. Even the CPU power connector (the 8-pin EPS) plugged into my Corsair AX Series Digital AX860i PSU's PCIe 3 port is at zero because all of the power everything needs to play "Free Bird" and keep Macromedia Dreamweaver open so I can type this (okay... Skype, Outlook and Chrome are open as well, but I digress) can be delivered via the 24-pin power connector. That's the 7.375A we see being reported above where it says "24 PIN ATX 12VA".
If I were doing something a little more productive with my PC right now, like converting all five seasons of the Muppet Show from AVI to MP4 so my daughter can watch them on her iPod (I think she found Elton John's outfit for Crocodile Rock scarier than anything in the Alice Cooper episode, but the singing crocodiles made watching it a more comfortable experience) we would see power, not only on the 24-pin, but also on PCIe 3 going up... like this:
Now that we have the CPU doing some work, we not only have 7.313A on the 24-pin power connector, but also 5.6875A on PCIe 3.
So how do we wake up those graphics cards? There's three of them and I'm not seeing ANY power output on any of the PCIe connectors other than PCIe 3. Well, we can always fire up Furmark...
There we go! You can see PCIe 1 with 11.25A on it. This has the highest load on it, other than PCIe 4, because it's the card that has to support the video output. PCIe 5 is the second power connector on that same card. PCIe 2 and 6 are for the second card. The reason PCIe 4 is showing 16.4375A is because there is one card, with two power connectors, using one connection on the power supply. The AX760i and 860i only have six modular interfaces for PCIe, but one of those connectors have to be used for the CPU. So Corsair makes one of the PCIe cables that comes with the AX760i and 860i a split cable: a cable that has one connector on one side, to plug into the power supply, and two connectors on the other side to plug into the graphics card. This essentially doubles the power output of this port.
You'll also note that I have the "enable OCP" box checked on all of my PCIe ports and that they're all turned down to 20A (the minimum setting. The maximum setting is 40A). I do that more to make a point of how OCP (over current protection) works and how even 20A can be more than adequate for a graphics card. Because if I were pulling more than 20A off of one graphics card, my PC would shut down.
We're putting out 730.9W, which apparently got the attention of Mr. PSU fan, because now, all of the sudden, he's woken up and is spinning at 908 RPM. But now we're not seeing anything on PCIe 3. Well, that's because Furmark stress tests the GPUs and not the CPU. If we want to see everything rocking, we can just go ahead and fire up Prime95 and we should start to see numbers on every connector, like this:
Now our PSU is putting out 771.6W and the fan has kicked up to 1016 RPM. That's because a 771.6W load on an 860W power supply is pretty significant. If I was using an AX1200i, I doubt we'd see the fan spinning that fast. You'll also note that the added load of the working CPU cores has not only put a load on PCIe 3, but has also increased the 24-pin's reading from 8.563A to 11.688A. Pretty cool, eh?
So what if I only have two graphics cards? Well, "Free Bird" is a long song, but it's now over and I can shut down my machine, pull out card #3 and fire it up again and see what happens.
A few moments later...
Ok. Now we're back up and running again and everything is the same except now there are only two of the GTX 670's running in the machine.
Just by removing the third card, I am using significantly less power. The power consumption at the 24-pin connector has dropped to 3.313A. I'm now only pulling 140.2W from the wall.
So what kind of effect does this have on my total system's power if I only load the CPU?
It looks like the measurement at the 24-pin hasn't moved any, but we're now measuring 5.8125A at PCIe 3 where the CPU's EPS12V power connector is hooked up. The AX860i is only putting out 194.6W. Even though the workload is really only on the CPU, I'm pulling 47 less watts from the power supply! So what if we load everything up?
It is interesting that now that I have the third card removed, we're measuring less power on the first card's first power connector. Perhaps because without the third card, we're displaying a lower frame rate and that requires less power from the first card. But some other things make more sense, such as the load on the 24-pin being lower. Since power from the 24-pin is feeding the CPU, the graphics cards via the PCIe slots, among other things. There's also more power going to the CPU now, via the EPS12V connector.
Also notice how out total system load is now only 529.8W. This is putting less stress on the PSU so the PSU fan only has to spin at 732 RPM to keep itself cool.
Now let's take it down to one card.
A little later...
So now we're down to one card and down to only 111.8W idle. That's a far cry from the 200.4W we saw initially when there were three cards installed. And when the CPU is under load?
I'm doing all of the same things with the PC before, but with only one graphics card installed. While I wasn't doing anything GPU involved before, the reading at the 24-pin is completely stuck at zero, even running Prime95. The load at PCI 3, on the other hand, is clearly delivering almost all of the power to the CPU as its reading is 5.8125A. At this time, we're only demanding 143W of the AX860i. So once again, even though I'm technically only working the CPU and the CPU hasn't changed, we're pulling 51.6W less now then when we had two graphics cards, just by pulling one of the cards.
And how much power are we using with both the graphics card and CPU being pushed?
It looks like we got some juice flowing through the 24-pin now, and we can see the one graphics card that's left installed. Our total power usage is 321W, which is pretty much half of what it was when we were running three cards. You can see here that, with the PSU running at less than half of its capability, the PSU fan doesn't even need to spin.
You know what's next, right? NO CARDS! Let's see what power consumption is like with just the Core i5 integrated graphics...
A lot of goose eggs there! And now, with Prime95 running...
Up to 134.9W. And now how much power does the Core i5 need to run Prime95 and Furmark?
Judging by the frame rate of Furmark (3 FPS. Yes.. three) and the fact that I could barely move my mouse across the screen, I believe we reached the maximum capability of this machine, which requires all of 141.5W.
But how bad is the performance? Well, you wouldn't think I'd go through all of this without running 3DMark 11 and getting a benchmark each time, would you?
|Integrated Graphics||Single GTX670||Two GTX670s
|3DMark Score||240 3DMarks||3093 3DMarks||5640 3D Marks||8097 3D Marks|
|Graphics Test 1||1.44 FPS||14.9 FPS||29.5 FPS||45.0 FPS|
|Graphics Test 2||1.26 FPS||14.3 FPS||28.4 FPS||43.1 FPS|
|Graphics Test 3||1.07 FPS||14.1 FPS||28.1 FPS||42.3 FPS|
|Graphics Test 4||0.53 FPS||8.8 FPS||17.6 FPS||26.2 FPS|
|Physics Test||19.2 FPS||22.2 FPS||17.7 FPS||22.2 FPS|
|Combined Test||1.25 FPS||15.7 FPS||24.7 FPS||29.1 FPS|
As you can see, by using a Corsair AX Series Digital ATX PSU and Corsair Link's power tab, I can see how much power my PC uses right down to each modular connector on the power supply, as well as my PSU's temperature and fan speed. Not only do we witness how much additional power multiple graphics cards use, even when they're not under load, but also how an AX860i power supply can remain absolutely silent, even under load, if it is not being pushed beyond 50% of its capability.