7900 GTO current from the 12V rail; how high is it really?

[Navid]

System:
Opteron 165 @ 300 X 9 = 2.7GHz @ 1.375V
2 X PC3200 Mushkin @ 300 X 9 / 14 = 192.8MHz
Asrock 939 Dual SATA
Seasonic S12 500
2 X Seagate SATA 300GB (one 7200.9 and one 7200.10)
7900 GTO 3D perf. @ 689 core 793 mem

Measurements performed using a Kill-A-Watt device. http://www.p3international.com/products/special/P4400/P4400-HG.html


The power input to my PSU at idle is 153W.

When running rthdribl, the input power is 224W. http://www.daionet.gr.jp/~masa/rthdribl/

When running 3DMark06, the power is about 244W during the 4 graphics tests. It fluctuated. It peaked to 252W a few times. But, most of the time it was at 244W or less. During the 2 CPU tests, the power was about 210W.

http://service.futuremark.com/compare?3dm06=543510

Let's concentrate on the highest power figure that I saw, which was 252W.

This is the manual for my power supply.
http://www.seasonicusa.com/images/BrochureManuals/NewS12Manual1.pdf

Seasonic claims that the power supply is very efficient (small power waste). They claim that the efficiency is 80% (see last heading on the first page). Let's say the power supply is REALLY efficient and has a 90% efficiency. This results in a very small waste of power. So, from the 252W power that I measured, 10% of it is converted to heat in the power supply.
252W x 10% = 25W

So, the remaining power is 252-25 = 227W.

I am intentionally making assumptions that would result in extra power consumption calculation for the video card. I want to show that even when I do that, the result is much less than what many assume.

This is my CPU. http://www.amdcompare.com/us-en/opteron/details.aspx?opn=OSA165CDBOX
According to this page, it consumes 110W. And don't forget that I am overclocking it by 50%. But, let's say it only consumes 70W.

So, 227 - 70 = 157W is what we have after taking into account the CPU.

This provides information about the hard drives. http://www.seagate.com/support/disc/manuals/sata/100402371a.pdf
The power consumption is specified to be about 9W (at idle) on page 31. I have 2 hard drives. That is a total of 18W. But, let's say the hard drives only consume a total of 10W. That leaves 157 - 10 = 147W.

Let's say all of this power is used by the graphics card from the 12V rail. This of course is very unrealistic. We are ignoring the power consumed by the RAM or the motherboard.

Then, the current of the graphics card can be calculated to be 147W / 12V = 12.25A.
So, even under these unrealistic imaginary conditions, the current of the graphics card is limited to only 12.25A.

 

[jiffylube1024]

Your graphics card is consuming way less than 150W - the 7900GTX has been tested to use ~90W if I'm not mistaken.

Also, your CPU should be consuming more than 110W that it's rated for, since to overclock that much, chances are you've upped the voltage.

-----------

Are you just doing a 'worst case scenario' ?

 

[Navid]

That is the whole point of this thread! To show that it consumes less than many suggest.
In another thread, someone suggested that it draws 22A from the 12V rail.

I just wanted to show that it consumes much less.
I guess you are confirming that. Thanks!

 

[P2Mc28]

Very Nice Thread =)

 

[Zebo]

I don't understand why you bumped up seasonics effcentcy to 90% when both seasonic and SPCR say it's 80-82%?

Also you're forgetting motherboard uses about 25-50W (NF4 on the higher end when OC'ed)

HDD use 20-25W when accessing.

No CD/DVD? Thats about 5W idle and like HDD's when accessing.

No 12V fans in your system?

In sum your calculations are way off. Adding my concerns it uses 80W just like xbit labs says a GTX uses...

 

[hans007]

supposedly a 7900GT uses just about 70 watts at full load. i'd imaging a GTO cant use much more than 95.

i know a x1900xtx gets up in the 130-140 range by comparison.

 

[Navid]

It sounds like everyone agrees that the card does not need 22A from the 12V rail!

Let me now recalculate making more realistic assumptions.

80% efficiency of the PSU means that 20% of the power is turned into heat. 252 X 20% = 50.4W. So, the remaining power is 252 - 50.4 ~ 202W.

Let's say the CPU uses 110W. That leaves 202 - 110 = 92W.

The hard drives take 18W. I am not accessing the hard drives while 3DMark test is running. So, that is why I am using the idle figure. That leaves 92 - 18 = 74W.

I have a DVD drive. Let's subtract 5W for that. 92 - 5 = 87W.

I have 4 fans in the system. They all run from low voltage. Let's say each of them takes 1W. That leaves 87 -4 = 83W.

This is Kingston not Mushkin. But, it is a similar RAM to what I have. I have two of these. http://www.valueram.com/datasheets/KVR400X64C3A_1G.pdf
So, let's take a total of 10W out for the RAM then.
83 - 10 = 73W.

This still leaves the motherboard out.

But 73W / 12V = 6A.
This means that the card takes less than 6 Amps.

So, yes Zebo, my calculations were very pessimistic. They still are conservative. That was intentional though. I didn't want anyone to say my calculations were too optimistic.

The problem I was hoping to address was the guys who post and tell people that they need a 700W power supply just because of the graphics card!

 

[Dethfrumbelo]

A 120mm fan on average should pull 0.3A at 12V, so let's say 3W per fan to be generous = 12W.

But it's true, the video card alone doesn't need anywhere near 22A, maybe 12A for a X1900XT worst case.

 

[bnlitin]

I am running my system with 7900GTO using a Seasoni S12-370W power supply with no issues.
The Seasonic has only two 12V rails, for a total of 25A. Since I don't hear the Seasonic fan speed up at all,
I don't think the GTO is really drawing too much current.

My system:
AMD X2 3800 @ 2.5GHz
4 WD SATA-2 500GB hard disks
2 DVD-RW
Audigy 2
7900GTO @ 700 MHzcore/800 memory
Seasonic S12-370W

 

[Navid]

Originally posted by: Dethfrumbelo
A 120mm fan on average should pull 0.3A at 12V, so let's say 3W per fan to be generous = 12W.

But it's true, the video card alone doesn't need anywhere near 22A, maybe 12A for a X1900XT worst case.

But, I do not run my fans at 12V. As I said, I have lowered the voltage in order to lower the noise. So, the power is lowered (second order also because power is proportional to voltage squared). That's why I picked 1W per fan.

 

[Pens1566]

Nice thread. Looks like everyone is just proving your point.

 

[VooDooAddict]

The AMD CPU power rattings are maxes, not actual draw.

 

[Navid]

Originally posted by: VooDooAddict
The AMD CPU power rattings are maxes, not actual draw.

Do you know where I can find the typical (actual) figure?

 

[lobbyone]

Nice stuff man, feel the POWER!