Determining CPU Wattage Output

[Fhqwhgads6680]

Hey guys, I was just curious what the forumla is for determining the approximate heat output in wattage of a cpu? I'm building a single stage and need to size my cap tube for my current cpu.

Also it would be nice to have some kind of formula for each given type of CPU. Obviously P4's aren't going to have hte same ratios as a64's etc. I'm sure this information is out there but I figured you guys would know and it would make this information handy and easy to find for others.

thanks!

[expansionvalve]

Ditto that ^^^^

[Levish]

Would 10-15% increase in TDP be safe to assume for every 200mhz for a64 opting for the 15% side if you are bumping vcore significantly to achieve the next speed bump?

i.e.
fx57 at 3000mhz should be roughly 114w (from 104wTDP)
fx57 at 3200mhz should be roughly 125w
fx57 at 3200mhz should be roughly 130w
fx57 at 3400mhz should be roughly 145w
fx57 at 3600mhz should be roughly 160w

btw I think dual core temps are understated with a fx60 at 110w

[Shinuza]

Could be right, but initial value given by AMD would be wrong :(

[_HL4E_HalfLife_]

You know there is a website out there that has a calculator programmed to give you a total system wattage but i've forgotten where the link to that website is.:confused: Im sure some of you know the site im talking about?

[_HL4E_HalfLife_]

Found it:D :banana: :toast:

http://www.extreme.outervision.com/index.jsp

Heres another one but will alot less to choose from

http://www.jscustompcs.com/power_supply/

[labrat23]

I think these programs are just taking your stock heat output and multiplying it by vcore^2 / stockvcore^2 * MHz / stockMHz. The hardest part is finding the true stock heat output.

[jinu117]

vcore ^ 2 / stock vcore ^ 2 scales actually exceptionally well from my experiments. It's the mhz part which I really didn't see much difference in heat output...

[_HL4E_HalfLife_]

The first link is the best one to get a cpu wattage because its all there just select ur cpu than click overclock my cpu. This is what i got for my cpu

Stock CPU speed (MHz) 3200
Stock Vcore (V) 1.525
Overclocked CPU speed (MHz) 3453
Overclocked Vcore (V) 1.525

Overclocked CPU Wattage: 88

If you set ur overclocked CPU speed and Vcore the same as ur stock it will just tell you ur default wattage (82 for me).

[jinu117]

problem is...
Once I put my dual core data in...
(opty 175, 3.05ghz 1.65v)... it says 228W... obviously it isn't pumping out that much heat. So.... again as I said, none of these programs are useful from what I've seen. (Sure... I am getting -42c evap with 228W heat with 1/4+ hp compressor lol)

[Shinuza]

Inital value given in datasheet is wrong.

Here is a way to calc it :
OC Watts = Stock Watts * (OC Mhz / Stock Mhz) * (OC Vcore / Stock Vcore)²

It the same as K * F * V²

Because you need to calc K

[SoddemFX]

K = 10-20nF depends on CPU. Take AMD / Intel TDP, and work it backwards with Voltage and Frequency to find K...

This is only a guideline for a "ball park" figure, this formula is not right.

You're just modelling it on capacitive power dissapation. It is much more complex than this...

But for us, "ball park" is good enough :)

Tom

[Shinuza]

Yep

And don't forget :

-Original TDP given in datasheet is almost everytime wrong
-It's an approximation
-Error Range will increase dues to the lower engraving technology

[Fhqwhgads6680]

Thanks guys, I appreciate the responses. I think I have a good estimate, wow didn't realize how much ocing these procs really cranks up the wattage. I knew it was alot, but according to these estimates my opty, at 1.68 and 3.25 ghz puts out nearly 200 watts! I thought I'd have to go Dual Core to see 200.....Thanks again!

[jinu117]

Thanks guys, I appreciate the responses. I think I have a good estimate, wow didn't realize how much ocing these procs really cranks up the wattage. I knew it was alot, but according to these estimates my opty, at 1.68 and 3.25 ghz puts out nearly 200 watts! I thought I'd have to go Dual Core to see 200.....Thanks again!

Aha...ha...ha... voltage you mentioned and 3.25ghz would be only about 140 watt actual load to 145w. Just shows you how this calculations don't really work well.

[Fhqwhgads6680]

So how do you estimate it then?

[jinu117]

I don't... :P
I plug cpu and load it up with condition... read evap temp at 2 diff places.
Than, I plug in my load tester with wattage reader and turn the knob till temp of evap matches... there is my real loaded wattage :) After taking few different spots of wattage reading, than I use interpolation. In case of dual core AMD, 1.73v(bios, 1.71mbm reading, actual 1.78v on mosfet using dmm) 3ghz dual priming was about 145-150 watt.
I did this just so that I don't have to turn on computer, etc to load test my single stages :)

[Fhqwhgads6680]

Gotcha, that makes sense. I am also curious what do you guys use as load testers? I am assuming a Peltier maybe?