Underclock/volt to reduce TDP and temps

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sethjaho

sethjaho

Commendable
Sep 8, 2016
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I want to reduce the tdp of my AMD A10 7850k from 95w to 65w. Is it possible? And how would I go about doing this? Please, only helpful responses. I am well aware that I could buy another processor, or other components to reduce temps. I am just wondering if and how I could do this.

Motherboard: GA-F2A88XN-WIFI (rev. 3.0, bios version f5)
CPU: AMD A10 7850k
 
Solution
Ecky
YMMV, but here's a chart showing the relationship between voltage and power consumption for the CPU in my signature:

AOb30Wd.png


^ With no undervolt, my CPU with a 4ghz OC draws ~79w more under load than at idle. Undervolted (and still overclocked) I can drop that down to 58w, a 25% decrease.

Here's a chart I made after painstakingly undervolting my CPU to the edge of stability at different frequencies:

mMBmP2A.png



At 4500mhz, my 3570K draws ~120w more under load than at idle.
At 4000mhz, it draws ~58w.
At the stock 3600mhz and with a healthy undervolt, my "77w" CPU draws 44w.
At 3000mhz, my CPU draws 26w.
At 2600mhz, my CPU draws 20w.

These are all measured with a Kill-a-watt...
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Ecky

Ecky

Illustrious
Feb 3, 2013
7,592
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TDP is not power consumption. Your CPU probably doesn't draw exactly 95w - many reviewers have noted that AMD's CPUs often draw more than their rated TDPs actually.

Nonetheless, lowering your voltage and clockspeed will reduce power consumption. Your CPU, running at the same clocks and voltage as one of AMD's 65w chips, will draw the same power as that CPU.

Later tonight I'll post some detailed information, but you can start by lowering voltage until your CPU becomes unstable, then bring it back up a few notches.

What's your reason for wanting to underclock?
 
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sethjaho

sethjaho

Commendable
Sep 8, 2016
3
0
1,510


Well, I understand that TDP, its more of a temp thing. Only reason is because I bought a Noctua NH-L9a and didnt realize its only rated for 65w CPUs. I'm running my machine in a Raven HTPC case. I really like the low profile build, and don't want to have to buy a new case, or another cooler. Thanks for the reply, by the way!!
 
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sethjaho

sethjaho

Commendable
Sep 8, 2016
3
0
1,510


I thought it was identical too! But the TDP guidelines state that it is rated for 65w
http://noctua.at/en/nh-l9a.html
Using AMD overdrive, I have reached uncomfortable temps during DAW work and gaming. I mean, my system is still stable, but it still definitely bothers me. Either way, is there a way to reduce TDP on this CPU with this mobo? Or would it not be worth it/ am I ok with the current setup? As I am typing this, my temp (according to HWmonitor) is around 51c.
 
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Ecky

Ecky

Illustrious
Feb 3, 2013
7,592
2
38,960
YMMV, but here's a chart showing the relationship between voltage and power consumption for the CPU in my signature:

AOb30Wd.png


^ With no undervolt, my CPU with a 4ghz OC draws ~79w more under load than at idle. Undervolted (and still overclocked) I can drop that down to 58w, a 25% decrease.

Here's a chart I made after painstakingly undervolting my CPU to the edge of stability at different frequencies:

mMBmP2A.png



At 4500mhz, my 3570K draws ~120w more under load than at idle.
At 4000mhz, it draws ~58w.
At the stock 3600mhz and with a healthy undervolt, my "77w" CPU draws 44w.
At 3000mhz, my CPU draws 26w.
At 2600mhz, my CPU draws 20w.

These are all measured with a Kill-a-watt at the wall, with idle power subtracted from load. Absolute idle draw is unknown but I imagine 5-10w is reasonable, so you can add 5-10w to these figures to get the total CPU power consumption in Prime95 torture testing, rather than just the delta between idle and load.
 
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