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Undervolting a CPU?

J

John G.

Limp Gawd
Joined
Jul 28, 2005
Messages
163
If I'm happy to run at stock speeds, should I tweak with the voltage so as to achieve lower CPU temps? They're usually a little higher than I'd like.

I'm running a 130nm 3500+, and I believe stock voltage for that is 1.5V. I think my mobo had it set to around 1.7V for some reason and I was getting temps of around 60C with my Zalman 7700AlCu. I backed it down to 1.50V in BIOS, but Everest reads CPU voltage as closer to 1.4V. Just curious if something was going on there.

Should I play around with the VCore to get it as low as possible? How will I know if it's too low-- does the same sort of stuff happen as when it's too high (instability, refusal to boot, etc)?
 
There's something wrong somewhere. You shouldn't get those temps with stock cooling, let alone with your solution.

Are you sure it's mounted right? Did you use thermal grease? Does your mobo report temps correctly? Does your case have any air circulation?

Anyway, if you get your issue with the temp figured out, you sure can undervolt to get lower temps. You'll know that you're too low if you get hangs, reboots, etc. If you get way too low, it may refuse to boot, but if you work your way down slowly it's more likely that the system will hang in Windows or bsod than refuse to boot altogether.

If I were you, I'd look into the CPU cooling issue itself and maybe your temps will be agreeable after that, but undervolting isn't bad especially if you have a way to reduce fan speed accordingly and silence your pc.
 
John G. said:
I'm running a 130nm 3500+, and I believe stock voltage for that is 1.5V. I think my mobo had it set to around 1.7V for some reason and I was getting temps of around 60C with my Zalman 7700AlCu. I backed it down to 1.50V in BIOS, but Everest reads CPU voltage as closer to 1.4V. Just curious if something was going on there.
Click to expand...

That would explain the uber temps... up to 1.7v from 1.5v for no reason at all (seems to me that would do it anyways).

The questions I have are:
Is that temp a load temp?
Did the temps go down after setting tot he correct voltage?

But regardless, undervolting will help you aceive lower temps / quieter machine. Just keep dropping the voltage by small increments untill you get to the point where it's not stable, then bump it back up a few notches.
 
It froze on me once at 1.5V so it's now at 1.55V, and seems to be running fine. The 60C temp at 1.7V was idle (yeah, bad, I know, but I didn't have instability problems so it wasn't a high priority). Now that it's at 1.55V, idle temp is now about 50C. A 10C drop is significant to be sure, but I would have liked/expected more.

The generally high-temps aren't a mystery to me though. I built the PC to be as quiet as possible, and I'll sacrifice a little life on my components to keep it that way. So only have two case fans, and they are low-CFM SilenX fans. My PSU is a "silent" PSU meaning its fan also is low CFM, and I keep the Zalman coolers on both my CPU and GPU (the VF700AlCu) on their "silent" settings.

Anyway, since 1.5V froze while loading Windows (though I only gave it that one chance), I think 1.55V is a good place to sit-- I can only lower temps so much while maintaining my need for a quiet PC. Yeah?
 
Undervolting's great. I managed to get my venice core 3000 down to 0.95V at stock speeds.

COUGHgetaveniceCOUGH :p
 
50c at idle for that cpu is still really hot, even with a stock heatsink you should be idling in the 20-30's, you really should check and make sure its seated well.
 
Yeah, 50 at idle isn't exactly what your going for, especially not with a highend heatsink.

Check it, if it was fine and you reseat it and nothing changes, it could be that the Mobo is FUBAR'd with it's temp readings.
 
Punx_Clever said:
Yeah, 50 at idle isn't exactly what your going for, especially not with a highend heatsink.

Check it, if it was fine and you reseat it and nothing changes, it could be that the Mobo is FUBAR'd with it's temp readings.
Click to expand...

That's what I was getting at. I had an Abit board that reported about 5C too high, but I knew it so it was fine. If his temps are accurate it's way too hot for the cooling provided, if they're inaccurate, they're still too high.

My rough guess is that you should have about a 12-15C difference between the Case temp and the CPU temp at idle. If it's more than that, I'd look at the HSF seating.
 
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