Power Consumption

Cooling modern video cards is becoming more and more difficult, especially when users are asking for quiet cooling solutions. That's why the engineers are now paying much more attention to power consumption of new video card designs.

For this test we measure power consumption of only the graphics card, via PCI-Express power connector(s) and PCI-Express bus slot. A Keithley Integra 2700 with 6.5 digits is used for all measurements. Again, the values here reflect card only power consumption measured at DC VGA card inputs, not the whole system.

We chose 3DMark03 Nature as a standard test representing typical 3D usage because it offers: - very high power draw - high repeatability - is a standard benchmark that is supported by all cards - drivers are actively tested and optimized for it - supports all multi-GPU configurations - easy to obtain - fairly compact in size - test runs a constant duration and renders a non-static scene with variable complexity just like any normal game.

The four result values are as following:

• Idle: Windows Vista Aero sitting at the desktop (1280x1024 32-bit) all windows closed, drivers installed. Card left to warm up in idle until power draw is stable.
• Average: 3DMark03 Nature at 1280x1024, 6xAA, 16xAF. This results in the highest power consumption. Average of all readings (12 per second) while the test was rendering (no title screen).
• Peak: 3DMark03 Nature at 1280x1024, 6xAA, 16xAF. Highest single reading during the test.
• Maximum: Furmark Stability Test at 1280x1024, 0xAA. This results in a very high non-game power consumption that can typically be reached only with stress testing applications. Card left running stress test until power draw converged to a stable value.
• Blu-Ray Playback: Power DVD 9 Ultra is used at a resolution of 1920x1200 to play back the Batman: The Dark Knight disc with GPU acceleration turned on. Playback starts around timecode 1:19 which has the highest data rates on the BD with up to 40 Mb/s. Playback left running until power draw converged to a stable value.

Even though ZOTAC uses the reference GTX 480 PCB at higher clock speeds than the normal GTX 480, the power consumption is considerably lower. I did check whether this reduction in power draw is caused by the new driver, but this does not seem to be the case. For me this is quite a mystery. One possible explanation is that the Amp! Edition on average runs cooler than the reference design. Higher temperature is associated with higher power draw, but whether that can make such a big difference I don't know.
Update May 27: I just tested the card again and stopped the fan manually and observed an interesting thing, when the card reached 92°C, the power draw was a lot higher in Furmark, in line with what I would have expected to see from a card like this. So the answer to the mystery of the low power consumption is simply "heat". Since the card runs so much cooler than the reference GTX 480, the power consumption is a lot less, only because the temperature is lower, there is no other magic happening here.

I did some additional measurements (using Furmark in a window so it's easier to control the fan speed) and found out that there is a linear relationship between temperature and power draw. The linear fit is y = 1.1975x + 215.29, so for every °C that the card runs hotter it needs 1.2W more power to handle the exact same load.



As a result the GTX 480 Amp! Edition shows very reasonable power draw numbers considering it's a GF100 based product. In order to beat ATI's latest offerings in terms of power draw NVIDIA still has some way to go though.