Radeon HD 6850 & 6870 CrossfireX review - Power Consumption - Cost Analysis

Power consumption

Lets have a look at how much power draw we measure with these graphics cards installed.

The methodology: We have a device constantly monitoring the power draw from the PC. We simply stress the GPU, not the processor. The before and after wattage will tell us roughly how much power a graphics card is consuming under load.

Our test system is based on a power hungry Core i7 965 / X58 based. This setup is overclocked to 3.75 GHz. Next to that we have energy saving functions disabled for this motherboard and processor (to ensure consistent benchmark results). On average we are using roughly 50 to 100 Watts more than a standard PC due to higher CPU clock settings, cooling, additional cold cathode lights etc.

With that in mind. Our normal system power consumption is higher than your average system.

Measured power consumption one 6850card

1. System in IDLE = 176W
2. System Wattage with GPU in FULL Stress = 278W
3. Difference (GPU load) = 102W
4. Add average IDLE wattage ~ 19W (ATI specified)
5. Subjective obtained GPU power consumption = ~ 121 Watts

Measured power consumption two 6850 cards

1. System in IDLE = 186W
2. System Wattage with GPU in FULL Stress = 393W
3. Difference (GPU load) = 207 W
4. Add average IDLE wattage x2 ~ 19W (ATI specified)
5. Subjective obtained GPU power consumption = ~ 245 Watts

Measured power consumption one 6870 card

1. System in IDLE = 173W
2. System Wattage with GPU in FULL Stress = 295W
3. Difference (GPU load) = 122 W
4. Add average IDLE wattage ~ 19W (ATI specified)
5. Subjective obtained GPU power consumption = ~ 141 Watts

Measured power consumption two 6870 cards

1. System in IDLE = 184W
2. System Wattage with GPU in FULL Stress = 421W
3. Difference (GPU load) =  237W
4. Add average IDLE wattage x2 ~ 19W (ATI specified)
5. Subjective obtained GPU power consumption = ~ 275 Watts

Mind you that the System Wattage is measured from the wall socket and is for the entire PC. Also measuring Multi-GPU setup is very tricky with IDLE states, so please see this as an indication.

Below a chart of measured Wattages per card. Overall this us much higher than reference, this is due to an increase GPU voltage to allow easy overclocking and the standard higher clock frequencies.

Power Consumption Cost Analysis

Based on the Wattage we can now check how much a card like today will cost you per year and per month. We charge 0,23 EUR cent (or dollar) per KWh (which is higher than the EU average).

We estimate and calculate here based on four hours GPU intensive gaming per day / 5 days a week with this card. Also make note of the fact that we explain what the GPU setup is costing you, not the entire PC power consumption.

Admittedly, in CrossfireX mode the power consumption is high, but really not bad at all.

Recommended Power Supply

Here is Guru3D's power supply recommendation:

Radeon HD 6850 x1

• On your average system the card requires you to have a 450 Watt power supply unit.

Radeon HD 6850 x2

• A second card requires you to add another ~130 Watts. You need a 650 Watt power supply unit.

Radeon HD 6870 x1

• On your average system the card requires you to have a 500 Watt power supply unit.

Radeon HD 6870 x2

• A second card requires you to add another ~150 Watts. You need a 700 Watt power supply unit.

The more you overclock and tweak, the more power you will use, adapt to that, we always advise you to get a power supply that is more capable then you'll use, have some reserves, please, do not let a PSU be a limitation.

There are many good PSUs out there, please do have a look at our many PSU reviews as we have loads of recommended PSUs for you to check out in there. What would happen if your PSU can't cope with the load?:

• bad 3D performance
• crashing games
• spontaneous reset or imminent shutdown of the PC
• freezing during gameplay
• PSU overload can cause it to break down

Let's move to the next page where we'll look into GPU heat levels and noise levels coming from this graphics card.