Power Distribution in Three PCs (2012)

Power | The Silent Front
Viewing page 2 of 4 pages. Previous 1 2 3 4 Next

TESTING METHODOLOGY

This time around we'll be testing three desktop PCs of varying power requirements to get a good cross section of data. We have a high power Nehalem based system with a 200W+ HD 5870 graphics card, a medium power Sandy Bridge machine with an HD 6870, and finally a low-end Athlon II PC with an entry level HD 5550 GPU.

Intel LGA1366 Test System:

Intel LGA1155 Test System:

AMD AM3 Test System:

Measurement and Analysis Tools

Testing Procedures

Each system is examined in various load states:

  • idle
  • playing H.264 video
  • encoding video with HandBrake
  • CPU load with Prime95
  • CPU+GPU load with Prime95 and FurMark simultaneously

System power consumption (AC) is measured with an Extech 38080. Current flowing through the +12V, +5V, and +3.3V rails is monitored using a Fluke 36. The individual wires in the various cable sets from the power supply were separated and then recombined according to the voltage they carried. In this way the total current from each individual voltage line could be measured separately. The -12V and +5VSB lines were not measured, as they carry so little current that they are insignificant (typically well under 5W).

Estimating DC Power

The following power efficiency figures were obtained for the Seasonic SS-650KM during review testing:

Seasonic SS-650KM Test Results
DC Output (W)
43
66
92
150
199
302
501
AC Input (W)
55
80
106
170
219
329
564
Efficiency
77.3%
82.6%
86.6%
88.3%
90.8%
91.7%
88.9%

Note that these efficiency figures won't match up with our results as our power supply testing is conducted using a purely resistive load and the proportions with which we load the various rails are dissimilar. Nevertheless it will be interesting to see how the efficiency differs under real world conditions.

Ambient temperature at the time of testing was 22°C.

LIGHT LOAD POWER TEST RESULTS

Most systems, especially those in the home, sit idle or are put under very little load during the majority of operation, performing mundane activities like checking e-mail, browsing the web, listening to music, and watching movies. For this type of usage pattern, saving 10W when idle is much more beneficial than 20W on load.

Power Distribution: Idle
System
i7-965 XE + HD 5870
i5-2500K + HD 6870
X4 630 + HD 5550
Pent. D 820 + GMA 950
Athlon 64 3500+ + 6800GT
+12V
(8-pin CPU)
0.8A
0.7A
0.8A
4.1A
0.6A
+12V
(6-pin GPU)
0.4A
0.3A
N/A
N/A
N/A
+12V Total
3.9A
3.2A
1.7A
4.6A
4.6A
+5V
0.9A
1.6A
1.8A
3.6A
3.0A
+3.3V
10.2A
2.5A
2.4A
0.7A
3.9A
Total DC Output
86W
55W
38W
76W
83W
Total AC Input
110W
77W
54W
-
-
Approx. Efficiency
78%
71%
69%

At idle, the Athlon II X4 630 system had the lowest total power draw at 54W AC (38W DC). The AMD CPU was paired with a low-end graphics card, but it should be noted that we previously estimated the idle power consumption of the HD 5550 at 15W, with the HD 6870 and HD 5870 at 18W and 22W respectively so the difference isn't huge. The i5-2500K rig was also equipped with a VelociRaptor rather than an SSD, accounting for a 4W difference (the SSD used with the other two system uses almost nothing).

The Athlon II X4 630 system had the most even power distribution, as did the Athlon 64 3500+ machine from six years prior, while the Core i7-965 XE machine relied heavily on the +3.3V rail. The Pentium D 820 and 3500+ drew a substantial amount off the +5V rail, but not so for today's systems. For a dual core CPU, the D 820's total power consumption was incredibly poor compared to its modern day quad core counterparts, especially as the Pentium system lacked discrete graphics.

The efficiency of our Seasonic X-650 power supply was noticeably poor at lower levels, but this is true of all power supplies. The efficiency curve of most PSUs typically peaks at the halfway point of the unit's maximum rated output.

Power Distribution: H.264 Playback
System
i7-965 XE + HD 5870
i5-2500K + HD 6870
X4 630 + HD 5550
+12V
(8-pin CPU)
0.8A
0.7A
1.1A
+12V
(6-pin GPU)
0.8A
0.5A
N/A
+12V Total
4.9A
5.3A
2.7A
+5V
1.5A
1.6A
2.1A
+3.3V
10.0A
2.7A
2.6A
Total DC Output
100W
82W
52W
Total AC Input
126W
105W
72W
Approx. Efficiency
80%
78%
72%

Little CPU power was used in the playing of H.264 video thanks to hardware acceleration being present in the Radeon HD 5000/6000 series. The minor increase in power draw over idle was mostly restricted to the +12V rail of all three systems with the GPU doing much of the heavy lifting.



Previous 1 2 3 4 Next

The Silent Front - Article Index
Help support this site, buy from one of our affiliate retailers!
Search: