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AM3 CPU Power Consumption
In our M4A78T-E review,
we noticed a significant power consumption discrepancy of up to 22W when using
an AM3 CPU on an AM2+ motherboard. Unfortunately the M4A78-HTPC/RC is also afflicted
by this anomaly, so it doesn't appear to have been an isolated case.
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Power Consumption: Phenom X3 720 (AM3)
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Test State
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M4A78-HTPC (780G AM2+)
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M3A78-T
(790GX AM2+)
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M4A78T-E (790GX AM3)
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Idle
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54W
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56W
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54W
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VC-1
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~91W
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~91W
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~71W
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CPU Load
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147W
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131W
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117W
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CPU + GPU
Load
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162W
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157W
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135W
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Systems configured with 2GB of RAM and 256MB IGP
memory.
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Using a Phenom II X3 720 processor, our test configuration's idle power was
similar to 790GX based M4A78T-E (AM3). Once any type of stress was placed on
the system, the board drew significantly more power as measured from the wall.
During video playback, we measured a 20W difference. This figure expanded to
30W when the CPU was placed on load. The results were similar to what we found
with the M3A78-T, only the
difference was even more pronounced, possibly due to poorer power regulation.
We've always found that high TDP chips tend to generate higher power consumption
on budget chipsets lacking in VRM cooling.
Cooling
Lower cost boards ship with simple heatsinks on the northbridge and southbridge
while those targeted at enthusiasts typically have large heatpipe coolers and
heatsinks on the voltage regulation modules near the CPU socket. A well-cooled
motherboard can deliver better power efficiency and stability.
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Heatsink Temperatures
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Measuring Point
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X2 4850e
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X3 720
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SB Heatsink
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45°C
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53°C
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NB Heatsink
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51°C
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66°C
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VRMs
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50~55°C
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80~90°C
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Measured with a spot thermometer after 10 minutes
of full CPU + GPU load. CPU fan reduced to 6V.
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The cooling on the board was very good when used with the X2 4850e processor.
The hottest spot on the northbridge and southbridge heatsinks measured 51°C
and 45°C respectively, while the VRMs registered in the low 50's. With a
Phenom II installed, we recorded significant increases in heatsink temperature,
though we could still place our fingers on them comfortably for long periods
of time. The VRMs, on the other hand, were burning hot — some extra cooling
here would not be amiss.
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