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Undervolting i7 920

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a b à CPUs
November 16, 2009 4:36:45 PM

So currently I have my i7 920 undervolted to 1.0875v (which shows up as ~1.055v in Windows, and goes to ~1.04v) from an initial 1.15v

I wish to undervolt it further...should I undervolt it to 1.05v base value, or should I go all-out and try to get it to 1.0v?

Has anyone even tried running their i7 920 at 1v or less?

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a b à CPUs
November 16, 2009 5:04:54 PM

why not just keep lowering it until its not stable anymore in prime95
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November 16, 2009 7:53:27 PM

From my initial 1.0875v (1.055v), my HWmonitor recorded the lowest power draw at 40.1 Watts.

At 1v (.96v), my lowest power draw is 46.12Watts

Why is my power draw higher? Is it because the system needs to keep the multiplier higher in order to maintain stability? It runs fine in Prime95.

Perhaps I should just increase the voltage...



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a b à CPUs
November 16, 2009 8:23:17 PM

So I'm at a crossroads here...

I can either keep my voltage at 1.05-1.0875v which causes my lowest power consumption to fall to 40watts at idle with temperatures not going over 59'C during Prime95...

OR

I can keep my voltage at 1v, which causes my lowest power consumption to increase to ~47watts (147watts max draw), and my cpu doesn't go over 53'C

Or

I can try to find a "sweet spot" between 1v and 1.05v which will result in my lowest power consumption falling to 40watts, and my max temps at 55'C or under.

*This 46watts at idle thing for 1v is really annoying... >_<
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a b à CPUs
November 16, 2009 8:47:42 PM

Its not always a good idea to undervolt. I know its seems like it would be the EXACT opposite of over volting, which is what we do to achieve higher MHZ than stock. Theres a lot of complexity to this, some background. I have a degree in electronics (ac/dc digital theory, 20 years ago, I took a diff career route) , I also have relatives and friends that work for the Electric utility. Long story short, low voltage to your house is BAD, to power your devices, to satisfy the voltage regulators and draw to make them work generally they have to draw MORE amperage to make up for less voltage. The chip is designed to work with the voltage regulator of your motherboard plugged in to a 120 volt outlet. Lowering your voltage at that point in the chain from 120 volts at your plug and to the 1.25 volt the chip needs (under some conditions) you are causing the chip to pull more amperage resulting in the higher wattage at idle. go back to all default settings , I bet your wattage at idle will go down. My I5 750 is at 29 watts at 3600mhz idle. the voltage on auto, all power saving features on, I just don't let it factory overvolt, in my case. In short your trying to be more efficient than the power saving features of the chip/ motherboard. Its not impossible to do, but I think your seeing a higher wattage is the result of what your doing being less efficient.
No I don't think you can hurt anything at all on this level.
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November 16, 2009 9:02:27 PM

notty22 said:
go back to all default settings , I bet your wattage at idle will go down. My I5 750 is at 29 watts at 3600mhz idle. the voltage on auto, all power saving features on, I just don't let it factory overvolt, in my case. In short your trying to be more efficient than the power saving features of the chip/ motherboard. Its not impossible to do, but I think your seeing a higher wattage is the result of what your doing being less efficient.
No I don't think you can hurt anything at all on this level.


I see. So you're saying my PC will actually save more energy by using a higher voltage for the CPU?


btw, I just brought it up to 1.05v, with actual voltage use defaulting to 1.0v~1.008v
My idle CPU temperatures increased by 1'C, and my idle CPU power draw fell by 4watts. Was the lowest possible power draw for the i7 920 at 40watts?
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November 16, 2009 9:20:13 PM

I'm not sure what the minimums are, we are also relying on sensors and software and not direct readings with a multimeter at the board level. But since all your tests are done with the same equipment way its somewhat scientific. Voltage to the chip area of your motherboard (regulators, capacitors,chip socket) gets its own 8 pin 2x4 12 volt connector from your power supply because this system is IMPORTANT and very controlled. You are dealing with around "1" volt at the chip , but in the end it pulls a 150 WATTS under load ! Its a interesting test, and the software to monitor it is very interesting. You could easily create a situation where you chip/thus your computer is very inefficient, even at idle and be totally unaware till your bill is higher.
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November 17, 2009 3:12:36 AM

Yeh, on the smallest voltage (1v setting, .95v), I pull 46w idle and 146w full load.
On 1.05 I pull 42w idle and 147 full load.
On 1.0875w I pull 40w idle and 149 full load.

The only diference is the amount of time I see the CPU in idle. When undervolted to 1v, I see the processor multiplier on max speed (x20, x21, x22) the majority of the time, so I'm using the full load power - it basically goes to full load power when my CPU usage is around 5% or more. (task manager info)

Whereas on higher voltages, even at 6-8% cpu usage I still only draw 43w idle and do not go into full load with max multipliers...
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November 17, 2009 3:25:26 AM

That's funny, why not just reinitiate speed step and watch it drop down to .9 volts and 5-10 watts in power usage according to everest

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a b à CPUs
November 17, 2009 1:13:30 PM

kg4icg said:
That's funny, why not just reinitiate speed step and watch it drop down to .9 volts and 5-10 watts in power usage according to everest

]http://i445.photobucket.com/albums/qq175/kg4icg/th_temps.png


Step speed is on. In my motherboard, it only drops the voltage if the settings are on auto. If I manually set it, it will remain at a constant voltage.
And on auto...it goes up to 1.2v at load, which is a bit too high for my taste for an i7 920 running at stock speeds.
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