4870 power consumption test with different core speed/mem speed/volts

[Shrekogre]

Test Bed

AMD Phenom II X3 720BE
Gigabyte GA-MA790GP-DS4H
Powercolor 4870 512mb reference card
VISTA X64 SP1
Running 2x RTHDRIBL to make sure the gpu loads at close to 100%
Power meter at socket looking at this
http://img26.imageshack.us/img26/3460/watt13vload.jpg (http://img26.imageshack.us/my.php?image=watt13vload.jpg)

http://img73.imageshack.us/img73/2043/13vload.jpg (http://img73.imageshack.us/my.php?image=13vload.jpg)

Core speed/ Mem speed and volts are varied to see the effects of power consumption.

Do note that the wattage reading is for the entire rig

[Shrekogre]

Stock core speed 750 mhz
Stock mem speed 900mhz
Stock volts 1.265v


Varying core speed
http://img16.imageshack.us/img16/7130/coregraph.jpg (http://img16.imageshack.us/my.php?image=coregraph.jpg)

Seem strange that changing the core speed on idle no effect on power consumption.

Varying mem speed
http://img24.imageshack.us/img24/4479/memgraph.jpg (http://img24.imageshack.us/my.php?image=memgraph.jpg)

Another strange result. Changing mem speed from 900 to 250 mhz on idle results in 30w power drop and 70w on load.

Varying core volts
http://img152.imageshack.us/img152/30/voltsgraph.jpg (http://img152.imageshack.us/my.php?image=voltsgraph.jpg)

This result is kind of expected but then wattage drop is lesser then that of when the mem speed is lowered.

Conclusion
Looking at the slope of the graphs, user can expect more power savings by reducing the mem clock followed by a voltage drop. this will result in roughly 40w savings. On load, nothing much can be done as lowering core and mem clocks will directly impact performance, however user can find the lowest possible voltage to run the speed required and that may save some power.

[Shrekogre]

My personal settings using RBE to flash bios

1.1v 250mhz core 250 mhz mem 2d

1.18765v 820 mhz core 1100 mhz mem 3d

stock is 1.2625v 750 mhz core 900mhz mem



http://img15.imageshack.us/img15/7227/4870modbiosyy8.jpg (http://img15.imageshack.us/my.php?image=4870modbiosyy8.jpg)

[MikeMurphy]

Great writeup! Thanks for taking the time to put this together.

I am still surprised that the gpu clock speed has no correlation to idle power consumption.

Any plans to measure the same on the gddr3 memory of the 4830/4850?

[celemine1Gig]

The thing about voltage having a somewhat limited impact on power consumption in comparsion to clocks is quite simple. Due to the small manufacturing processes, the chips don't need much voltage to operate, to start with. So the impact of the changed voltage (U²/R, or the deltas) isn't as high as it used to be when VCC needed to be much higher, because of the larger manufacturing processes. And although the clocks "only" have a linear influence on power consumption, they become more and more important, as they keep on increasing with each new die shrink.
Nice to see that reality is on par with theory here. :)

[SpeedEuphoria]

Any plans to measure the same on the gddr3 memory of the 4830/4850?

I can verify that on my 4850 reducing the mem speeds reduced Idle power consumption. For mine stock is 1050 mem, lowering it as far as I can, which is 600mhz reduces idle power consumption by 15w. Lower than 600Mhz mem gives me artifacts just sitting at the desktop.

Also a note, is that on mine I can lower the gpu core, with reduced voltage, then it wont go below 250mhz w/o adding voltage back, very strange.

Anyway here is another great article for video card power consumption:
http://ht4u.net/reviews/2009/power_consumption_graphics/

[Shrekogre]

I can verify that on my 4850 reducing the mem speeds reduced Idle power consumption. For mine stock is 1050 mem, lowering it as far as I can, which is 600mhz reduces idle power consumption by 15w. Lower than 600Mhz mem gives me artifacts just sitting at the desktop.

Also a note, is that on mine I can lower the gpu core, with reduced voltage, then it wont go below 250mhz w/o adding voltage back, very strange.

Anyway here is another great article for video card power consumption:
http://ht4u.net/reviews/2009/power_consumption_graphics/

I saw someone posted that going too low a vcc will cause the mobo not to recognise the card on post. I do have problem going below 250mhz for core. Intermittently getting gpu recovery when its trying to switch to 3d.

anyway I do not have a 4850/30 to try.

[largon]

Since you have a reference HD4870 with Volterra digital PWM you would get very accurate GPU amperage readings, and as such GPU wattage out of RivaTuner by enabling the plugin.
;)

[Shrekogre]

Since you have a reference HD4870 with Volterra digital PWM you would get very accurate GPU amperage readings, and as such GPU wattage out of RivaTuner by enabling the plugin.
;)

ah you are right. i thought it wouldn't measure the gddr5 amperage but I did not verify. guess it could.

[kipow]

nice test, my 8800gt consume like that on load.