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HEAVY LOAD POWER TEST RESULTS
The amount of power consumed on heavy load is a determining factor in how much capacity is required for a power supply and how much cooling is required to keep things running smoothly. Like all electrical components, CPUs, GPUs, and motherboard VRMs aren't 100% efficient, resulting in waste heat during operation. The more energy the system draws, the more heat needs to be dissipated, so bigger heatsinks and faster, louder fans might be required.
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Power Distribution: HandBrake Video Encoding
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System
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i7-965 XE + HD 5870
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i5-2500K + HD 6870
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X4 630 + HD 5550
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+12V
(8-pin CPU)
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7.5A
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4.2A
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5.2A
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+12V
(6-pin GPU)
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0.4A
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0.3A
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N/A
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+12V Total
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11.2A
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6.5A
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6.2A
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+5V
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1.5A
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1.7A
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2.9A
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+3.3V
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9.7A
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2.4A
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2.4A
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Total DC Output
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175W
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96W
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97W
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Total AC Input
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204W
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123W
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119W
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Approx. Efficiency
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86%
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78%
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82%
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Our first heavy load test is encoding a video using HandBrake, a tool commonly used to re-encode video formats so that they're compatible with various devices. It's purely a software encoder, using CPU power to do all the work. As a result, almost all the extra load came on the +12V lines with some marginal increases on the +5V rail for the i7-965 and X4 630.
For many users, this may be the most stressful thing performed on their system and yet the total system power consumption was quite low, about 120W AC for both the Sandy Bridge and Athlon II based machines. The i7-965 is a bit antiquated and inefficient and even it used only ~200W.
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Power Distribution: Prime95
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System
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i7-965 XE + HD 5870
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i5-2500K + HD 6870
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X4 630 + HD 5550
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Pent. D 820 + GMA950
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Athlon 64 3500+ + 6800GT
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+12V
(8-pin CPU)
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8.9A
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4.8A
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6.2A
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11.0A
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4.0A
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+12V
(6-pin GPU)
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0.4A
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0.3A
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N/A
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N/A
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N/A
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+12V Total
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12.7A
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7.3A
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7.2A
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11.4A
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7.8A
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+5V
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2.1A
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2.6A
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3.5A
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3.5A
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3.8A
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+3.3V
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10.2A
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2.2A
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2.6A
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0.6A
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3.8A
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Total DC Output
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198W
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109W
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113W
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155W
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125W
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Total AC Input
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229W
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134W
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134W
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-
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Approx. Efficiency
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86%
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81%
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85%
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Note: The older Pentium D and Athlon 64 systems were tested with CPUBurn rather than Prime95.
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Using Prime95, a synthetic CPU stress tool, again most of the extra power is derived from the +12V rail with some moderate increases on the +5V rail. The total power consumption was not that far off from our video encoding test, about 10~25W more.
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Power Distribution: Prime95 + FurMark
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System
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i7-965 XE + HD 4870 CrossFireX
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i7-965 XE + HD 5870
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i5-2500K + HD 6870
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X4 630 + HD 5550
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+12V
(8-pin CPU)
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9.0A
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9.2A
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4.9A
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6.0A
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+12V
(6-pin GPU)
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15.2A
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12.1A
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7.4A
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N/A
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+12V Total
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36.0A
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28.3A
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17.8A
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9.3A
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+5V
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2.3A
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2.3A
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2.5A
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3.5A
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+3.3V
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12.2A
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10.6A
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2.6A
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2.7A
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Total DC Output
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484W
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389W
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237W
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139W
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Total AC Input
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547W
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438W
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271W
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162W
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Approx. Efficiency
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88%
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89%
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87%
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86%
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The real party didn't begin until we threw FurMark into the mix, a tool used to stress graphics cards more than actual gaming. Once again, the +12V rail ruled supreme, but this time the 6-pin PCI-E power cables provided much of the extra load. The HD 5870 and 6870 are fairly power hungry, doubling the total power consumption of their respective systems, while the HD 5550 didn't make much of a dent.
Our video card selection is somewhat limited (the HD 5870 is our highest draw card, using about 220W on load) so to show you what you can expect with a more high-end configuration we added results with a pair of HD 4870s in CrossFireX on the i7-965 machine. The older 4870s are notoriously inefficient, taking the AC input of the Nehalem PC up to 547W. Even combining components with intentionally power sucking hardware, our 650W power supply was only pushed to about 75% capacity.
This is the type of activity that allows power supplies to reach peak efficiency
levels, with our test unit exceeding 85%. It should be noted that in our X-650
review, efficiency reached up to 92%. The discrephancy is likely the result
of a combination of three factors: the difference in load distribution in our
power supply testing, the different type of load (resistive) we use to stress
power supplies, and to a lesser degree, the inaccuracy of our clamp meter. As
a result the real world efficiency was up to 10% lower in some cases.
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