AMD 7950 uses 45W more when HDMI in use

[Sylent]

I recently built a PC with an i7 3770 (non-K) in a Z77 mobo with 8GB RAM, 2 SSDs, 1 HDD and a Sapphire 7950. The GPU has 1 DVI, 1 HDMI and 2 mini-DP ports.

I was testing power comsumption at the wall tonight. I'm in a 240V region. If I connect a monitor to DVI or mini-DP the PC draws about 60W at the wall while idle. If I connect the same monitor to the HDMI port via the Sapphire-supplied HDMI to DVI adapter the PC draws 105W from the wall while idle.

Is this normal?

I run 3 Dell 23" monitors in the H configuration, currently 1 DP, 1 HDMI and 1 DVI. I'm wondering whether I could drive them with 2 DP and 1 DVI and save a constant 45W.

 

[RussianSensation]

Sorry, you have to explain it more:

Does the power consumption go up when you connect 3 monitors or just switch from DVI to HDMI-to-DVI adapter with even 1 monitor?

The HDMI and DVI share bandwidth and now your card knows it's using 2 monitors over a digital connection. At this point the 2 monitor power consumption kicks in, which is higher than over 1 monitor. The power consumption increases on a 7950 card when driving 2 or more monitors over HDMI/DVI.

If you have DP ports on the Dells and have extra cables, you could try that but I am not sure if will fix it. I believe only GTX600 series can drive 3 monitors and have the same idle power consumption as with 1.

 

[Sylent]

Sorry, I should have been clearer.

Although I do normally run 3 monitors, I did this power testing with just 1 monitor hooked up. With a single monitor, the PC uses 45W more when driving the display from the HDMI connector (105W) compared to using a mini DisplayPort connector (60W).

I tested further and found that with 2 monitors, using 1 mini-DP and 1 DVI, the power draw at the wall remains at 60W.

I think I will have to order another DisplayPort cable to find out whether I can have 60W running with 3 monitors.