I've recently built an HTPC primarily for running XBMC under Windows 7, but also for occasional Bluray playback. I am using an older Socket 1156 H55 motherboard (Gigabyte GAH55M-USB3) and a Clarkdale i3-540 processor with integrated IGP (Intel HD 3000 I think).

To make a long story short, I am seeing a much higher than expected jump in both idle and video playback power consumption between an IGP-only system, and the exact same system with a discrete video card, and I can't figure out where the extra power is going.

With the IGP only, the system idles at around 45W. Playing a typical video with XBMC only seems to add a couple of watts. But when I plug in a Radeon HD 6770, the idle power skyrockets to around 85W. That's a 40W jump (using the latest Win7 Catalyst x64 drivers from Jan 2012). Again, not much difference between idle and playback power consumption, so I don't think it has anything to do with the video decoding load.

I was under the impression that the 5770/6770 generation of video cards had idle power in the 15W ballpark. Figuring in 5W or so for PSU inefficiency (Antec Earthwatts 380) and general Kill-A-Watt inaccuracy, that leaves at least 20W unaccounted for. Is this normal for an H55/Clarkdale system? Is the mere presence of an external video card perhaps causing some other part of the CPU/motherboard to come awake and consume large amounts of power? Maybe something in the southbridge? Would a Sandy Bridge do better here?

Unfortunately (or perhaps fortunately) I had to return the 6770 which was a loaner from a friend, but I do have a new Sapphire 7750 card on order. I'm hoping that one fares better but it seems like something else in the system is dominating the power consumption.

Which version of XBMC are you using? I've tried various versions -- the earlier ones always had high GPU loading. Too high for low power usage, imo. The latest, 11 (in various revs), has much lower GPU load & is considerably faster in general. You should check idle power in Windows and playing the same videos with something like Media Player Classic & compare with XBMC numbers.

With a Phenom2 quadcore, I get ~40W idle in XBMC. typically 10W higher playing HD video.

I'm using XBMC 11 (Eden) RC2. Unfortunately I no longer have the 6770 to test, but shortly after posting, my new Sapphire 7750 arrived a day early, so I'm testing it now.

It looks like things have vastly improved. Using the latest Catalyst drivers (which I had to download from Sapphire, because the 12.2 drivers at AMD's site don't recognize this card for some reason, even though they're supposed to add support for the 7000 series), I get a Win7 desktop idle power of around 52-53W, so the card adds about 7W idle power compared to just the IGP.

Running Furmark 1080p, I peak at around 101W.


Using Windows Media Player, and playing the sample video at: C:\Users\Public\Videos\Sample Videos\Wildlife.wmv:

67W



XBMC 11 RC2, playing from a network share:

C:\Users\Public\Videos\Sample Videos\Wildlife.wmv: 65W
Ripped Bluray ISO (1080p): 68W
Xvid-encoded 720p .mkv: 64W


So it looks like my system is back to sanity. Something must have been weird about that 6770, or the video driver.