8-way SLI and Crossfire Power Supply (PSU) Roundup

Power Consumption

Did you know that power supplies play a major role when it comes to power consumption in desktop comupters? I knew that it would make a difference, but not nearly as large of a difference as we found during testing. A 76W difference was noted on our AMD AM2 test platform, and after doing a little research, power supply efficiency is the reason behind the huge power consumption difference. The other critical thing when it comes to power consumption is Power Factor Correction (PFC).

The most efficient power supplies have Active Power Factor Correction (Active PFC). Active PFC power supplies use a circuit to correct the power factor, which menas Active PFC power supplies are able to generate a theoretical power factor of over 95%. Active Power Factor Correction also markedly diminishes total harmonics, automatically corrects for AC input voltage, and is capable of a full range of input voltage. Active PFC is the more complex method of Power Factor Correction, so it is more expensive to produce an Active PFC power supply. Non-PFC power supplies are no longer recommended by many system builders and believe it or not, in Europe, power supplies are now required to have either active PFC or passive PFC.

Full Load Efficiency Ratings:

Power Supply Model	Efficiency %	Active PFC
Aerocool Zerodba 620	Not Listed	NO
Antec Neo HE 550	up to 85%	YES
Mushkin XP650	up to 73%	NO
OCZ PowerStream 600W	up to 73%	NO
OCZ GameXstream 700W	up to 80%	YES
Thermaltake ToughPower 550W	up to 80%	YES
Thermaltake ToughPower 750W	up to 85%	YES
Ultra X-Connect 2 550W	up to 71%	NO

AAccording to the efficiency chart above, we should see the Thermaltake Toughpower 750W and the Antec Neo HE 550 drawing the least amount of power under full load. Since power savings is a huge deal in todays market many are looking for a “green friendly” solution to the market. When looking at the below charts, keep in mind that the lower the number, the more efficient the PSU; thus, the more money you will save!

Looking at the AMD/SLI chart, we see that at idle, most of the PSUs are very close in power usage. The OCZ 600W PSU, Ultra 550W, and Thermaltake 550W are a little high in power usage when at idle. However, the bigger difference comes when under full load. Here we see the difference between using lower quality and high-efficiency components and Active PFC. This chart shows the Antec Neo HE 550, OCZ GameXStream 700W and Thermaltake ToughPower 750W as being the three most efficient power supplies under full load. The difference in the most efficient to the least efficient was found to be 76W under full load.

What does 76W mean to you? Electricity is measured in kilowatt-hours and the current charge for electricity varies from state to state. Since pricing varies from state to state and during seasons let’s just use $0.14 per kilowatt-hour for pricing to figure up some rough numbers.

Cost Estimates:

• 24 hours a day – $7.78 per month or $93.28 yearly
• 8 hours a day – $2.60 per month or $31.10 yearly
• 4 hours a day – $1.30 per month or $15.55 yearly

Since I keep my computer on nearly 24 hours a day and fold 24/7 on it for the Legit Folding Team (Team #38296) it might actually be a smart move to move over to a power supply that is more efficient. If you are running your systems under full load, meaning both processor and graphics card for extended periods of time the efficiency of the power supply is something to base your purchase around! With that said let’s take a look at the Intel numbers.

This chart confirms the previous chart by labeling the same three PSUs as highly efficient. So regardless of how these PSUs are advertised, we are showing real world results and can easily see which ones carry a higher efficiency rating. When comparing power supplies, remember these charts and understand that while you may pay a slight price premium for a higher efficient power supply, you will save money in the long run!