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Temperatures & Voltage (specifically mobile 2500+)

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roll+call

Member
Joined
May 31, 2004
Location
ontario, canada
Okay, is there anyway of telling how high in temps you can safely go with a cpu based on voltage? I'm told that as you increase voltage the max temp decreases.. so if at 1.45V the mobile 2500 can handle up to 100C then it could never do that at 1.65V
Anyone know the relationship between voltage and temperature? Thus far I've pretty much stayed away from anything over 50C load (about 1.725/1.75 on air).

As a supplement, if I raised voltage progressively would I sooner have problems simply getting it stable or could I get it stable and still mess up the cpu (assuming the cpu could handle the relevant core speed).

TIA
 

hitechjb1

Senior Member
Joined
Feb 2, 2003
This may not directly address your question, but it is about the general relationship between temperature and voltage for overclocking, ....

hitechjb1 said:
What is an ideal and safe temperature for overclocking

I think there is NO single ideal or safe temperature in overclocking, temperature varies with CPU voltage and frequency. The AMD tech doc specifies some absolute temperaute limit, but that is way higher than normal usage temperature. Here is why.

With ambient temperature around 20 - 30 C (summer is coming), below is the general picture.

For stock cooling, one should be able to get 2.1-2.2 GHz out of it, temperature can get to somewhere between 55 - 65 C.

For Volcano 9/11/12, probably one can add 100 MHz to get it to 2.2 - 2.3 GHz, with temperature somewhere between 50 - 60 C.

With a good copper HS such as SLK-947/SP-97 and a high speed adjustable fan such as Thermaltake Smart Fan II, one would expect to get around 2.3-2.4 GHz from a desktop barton with temperature somewhere between 50 - 55 C; and 2.4 - 2.6 GHz out of a mobile barton with temperature somewhere between 40 - 50 C.

All these numbers are for general reference to illustrate the trend, don't take them as 100% rigid.

Generally, most people would put a fix number of max temperature, say 60 C or 55 C or 50 C on the CPU, it is fine as a first order guideline.

Technically, CPU temperature and CPU stable frequency vary inversely, higher frequency requires lower temperature for stability and lower frequency can work stably at a higher temperature.

E.g.
- A CPU can run stably at a much higher temperature (e.g. 60+ C), at a lower Vcore and lower frequency (e.g. 1.4 - 1.6 V, 2.2 - 2.3 GHz for Tbred B/Barton) than its intrinsic ideal max frequency.

- A CPU needs a much lower temperature (e.g. under 30 - 45 C on air or even lower for extreme cooling) to run stably at high Vcore for sustaining a higher overclocking frequency (e.g. 1.8 - 2.0+ V, 2.5 - 3.0+ GHz).

For technical details:

Originally posted by hitechjb1
...
The higher the voltage and frequency, the higher the power and the higher the temperature. Such active power will increase the CPU to certain temperature under certain load for a given cooling.

Since carrier mobility decreases as temperature increase beyond certain temperature due to lattice scattering, transistor switching slow down as temperature increases. So the frequency f of a CPU varies inversely with the temperature, or df / f = - k dt, mathematically, where f is frequency, t is temperature, and k is a constant.

The balancing of these two opposing actions, or the intersection of the voltage-frequency curve and the temperature-frequency curve of a CPU characteristic naturally determines the final stable voltage/frequency/temperature operating point. If overclocking is done properly, the maximal overclocking should settle naturally at certain frequency, voltage and temperature, as desribed above, below the maximum absolute rating of voltage and temperature (as seen from Tbred/Barton, ...). A perceived stable voltage and temperature setting may not be necessary after all, if the voltage, temperature, frequency variations are monitored properly and adjusted incrementally.

CPU voltage: from stock to max absolute, from efficient overclocking to diminishing return (page 19)


Relationship between CPU frequency and temperature (page 20)

Why high voltage is needed to run higher CPU frequency (and maybe higher FSB) (page 20)
 
OP
roll+call

roll+call

Member
Joined
May 31, 2004
Location
ontario, canada
That certainly helps plenty! :)
Now, just to make sure I've got some grip of things..

From CPU voltage: from stock to max absolute, from efficient overclocking to diminishing return (edited):
hitechjb1 said:
1. For Tbred B/Barton, the default voltage ratings (stock voltage) are
- For mobile Barton, 1.45 V
...

2. The max absolute voltages that AMD put up are:
Quoted from AMD:
"The AMD Athlon XP processor model 8 should not be subjected to conditions exceeding the absolute ratings, as such conditions can adversely affect long-term reliability or result in functional damage."

- For DLT3C, e.g. 1700+ DLT3C
Vcc_core_dc_max = 1.5 + 0.05 = 1.55 V
The absolute rating for Vcore = 1.55 + 0.5 = 2.05 V
...

For mobile Barton which the model 8 and 10 tech doc do not cover, but since mobile Barton is a derivative from Tbread B + Barton, so its max absolute voltage should resemble that of Tbred B 1700+ DLT3C.
...

3. For overclocking, the "efficient overclocking voltage" that gives the most overclocking frequency and keeps temperature below diminishing return is
- between 1.5 to 1.85 V for DLT3C and mobile Barton,
- between 1.6 to 1.95 V for DKT3C and desktop Barton
getting about 100 - 130 MHz per 100 mV.
...
4. If one needs to get the last MHz (last stable 50-100 MHz) from the CPU, then the CPU has to operate above the "efficient overclocking voltage" and below the "max absolute voltage" . The CPU would have to operate in the diminishing return regime in which every mV of voltage added to speed up the CPU frequency would be counter-acted by the heat increase which in turn slow down the CPU. The return of MHz from voltage is small (< 30 MHz per 100 mV, < 10 MHz / C) and is costly in term of cooling, power supply in this operating range.

This voltage range is recommended for benchmark testing and competition, and not necessary for 24/7 usage. If one has only a CPU to rely on, don't operate it constantly in this voltage range.
...
From How to determine "highest" voltage and temperature for CPU overclocking (edited):
hitechjb1 said:
...
So unconditional increasing Vcore (even system is operational) for little MHz gain is not desirable for 24/7 usage, the break-even number (that I use) is 30 MHz / 100 mV.

It is estimated for certain metal that an increase of temperature by 20 C over nominal max temperature would roughly result in doubling the electromigration rate, hence shortening the failure time to 50%. I would put a temperature safety cap of 65 C, which is 20 C below the max temperature rating of 85 / 90 C for Tbred B/Barton.
So, for a mobile barton raising voltage between the 1.5-1.85V range as much as possible while keeping temps below 65C (or 60C for safe measure) should be okay? Am I getting this right?
It's temps that I'm most concerned about as those seem to have the least definite values. My main question I suppose, is if I up voltage progressively will I reach a point of complete instability before I run the risk of messing up my cpu due to high temps (ie. is it possible for it to be prime/memtest stable while still being capable of damaging the cpu). My assumption is I'd notice things going wrong way before damage.
I'm on air btw: SLK-800U w/ an 'decent' 90mm fan (off a friend and forget the cfm)
Excellent posts hitechjb1, you certainly know what you're talking about!
:cool:

Thanks
 

Docta_Z

Member
Joined
Aug 6, 2002
Location
Canada
Personally I wouldn't exceed 55 C at load. 60 is much too hot imho.

Idle should be < 50 C...
 

hitechjb1

Senior Member
Joined
Feb 2, 2003
roll+call said:
That certainly helps plenty! :)
Now, just to make sure I've got some grip of things..

More importantly and additionally, don't miss these important aspects about temperature for stable operation, i.e. temperature varies with voltage and frequency for stable operation.

hitechjb1 said:
...
Generally, most people would put a fix number of max temperature, say 60 C or 55 C or 50 C on the CPU, it is fine as a first order guideline.

Technically, CPU temperature and CPU stable frequency vary inversely, higher frequency requires lower temperature for stability and lower frequency can work stably at a higher temperature.

E.g.
- A CPU can run stably at a much higher temperature (e.g. 60+ C), at a lower Vcore and lower frequency (e.g. 1.4 - 1.6 V, 2.2 - 2.3 GHz for Tbred B/Barton) than its intrinsic ideal max frequency.

- A CPU needs a much lower temperature (e.g. under 30 - 45 C on air or even lower for extreme cooling) to run stably at high Vcore for sustaining a higher overclocking frequency (e.g. 1.8 - 2.0+ V, 2.5 - 3.0+ GHz).

hitechjb1 said:
...
The balancing of these two opposing actions, or the intersection of the voltage-frequency curve and the temperature-frequency curve of a CPU characteristic naturally determines the final stable voltage/frequency/temperature operating point. If overclocking is done properly, the maximal overclocking should settle naturally at certain frequency, voltage and temperature, as desribed above, below the maximum absolute rating of voltage and temperature (as seen from Tbred/Barton, ...). A perceived stable voltage and temperature setting may not be necessary after all, if the voltage, temperature, frequency variations are monitored properly and adjusted incrementally.
 

hitechjb1

Senior Member
Joined
Feb 2, 2003
roll+call said:
That certainly helps plenty! :)
...

So, for a mobile barton raising voltage between the 1.5-1.85V range as much as possible while keeping temps below 65C (or 60C for safe measure) should be okay? Am I getting this right?
It's temps that I'm most concerned about as those seem to have the least definite values. My main question I suppose, is if I up voltage progressively will I reach a point of complete instability before I run the risk of messing up my cpu due to high temps (ie. is it possible for it to be prime/memtest stable while still being capable of damaging the cpu). My assumption is I'd notice things going wrong way before damage.
I'm on air btw: SLK-800U w/ an 'decent' 90mm fan (off a friend and forget the cfm)
Excellent posts hitechjb1, you certainly know what you're talking about!
:cool:

Thanks

So, assuming the following is valid:
hitechjb1 said:
E.g.
- A CPU can run stably at a much higher temperature (e.g. 60+ C), at a lower Vcore and lower frequency (e.g. 1.4 - 1.6 V, 2.2 - 2.3 GHz for Tbred B/Barton) than its intrinsic ideal max frequency.

- A CPU needs a much lower temperature (e.g. under 30 - 45 C on air or even lower for extreme cooling) to run stably at high Vcore for sustaining a higher overclocking frequency (e.g. 1.8 - 2.0+ V, 2.5 - 3.0+ GHz).

For your voltage of 1.5 - 1.85V for mobile barton, with an estimated frequency range of 2.3 - 2.6 GHz, I would say the max temperature on air needed for stable operation be between 65 - 45 C CPU diode temperature. Again, temperature and frequency vary inversely, e.g. 65 C for 2.3 GHz, and varies to 45 C for 2.6 GHz.
 
OP
roll+call

roll+call

Member
Joined
May 31, 2004
Location
ontario, canada
Gotcha, thanks for the help. It's looking like it's falling into that groove :p
Running at 2475 now @ 1.775V. Stopped p95 after 2.5 hours but I'll do the full test later. If not stable then I may flirt with 1.8V or drop fsb a bit. More likely do the latter.
Temps are 45/46 idle and about 52/53 load... may be pushing the bounds a bit, but if the system is stable then should be okay.
 
OP
roll+call

roll+call

Member
Joined
May 31, 2004
Location
ontario, canada
hitechjb1 said:
For your voltage of 1.5 - 1.85V for mobile barton, with an estimated frequency range of 2.3 - 2.6 GHz, I would say the max temperature on air needed for stable operation be between 65 - 45 C CPU diode temperature. Again, temperature and frequency vary inversely, e.g. 65 C for 2.3 GHz, and varies to 45 C for 2.6 GHz.
Falls almost exactly in there... a bit over halfway in freq., and temps just under half :p