Power Supply draw

Posted on 2006-07-07
Last Modified: 2013-11-08
Hi all,

I'm thinking of upgrading my GPU to the new GeForce 7950GX2. What I want to know before I shell out 500 euro :-) is whether my PSU can handle it. I'm just wondering is there any utility or method I can use to calculate the total current my PC draws from my PSU? Any help is appreciated!


Question by:pushpop
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Expert Comment

ID: 17057304
Any motherboard monitoring software should display your current voltages on the different 'rails' of your PSU.

What PSU do you have? What wattage? What combination of optical and hard drives? Number of case fans? All these are factors which will contribute to your PSU's stability and how it will cope with a powerful graphics card added.

Author Comment

ID: 17057373
My machine specs are as follows:

AMD Athlon 64 X2
1GB PC3200 DDR

GeForce 7300
SoundBlaster 7.1
16X DVD-RAM writer
Floppy drive

Four case fans


Author Comment

ID: 17057376
oops and PSU is 420W
LVL 91

Expert Comment

ID: 17057404
calculate what you need here :            
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Expert Comment

ID: 17057408
I think it should be ok as you've only 1 optical and 1 fixed disk, even running 2 cards in SLI i wouldn't expect problems on a 400W+ PSU :)

Expert Comment

ID: 17057448
Great link nobus!

Using the above specification and choosing the highest use of wattage for all the options the total comes out at ~300w, so well within the capabilities of your current PSU! :)

Author Comment

ID: 17057482
That's a great link thanks, i got 316!

One thing however, my card will be PCI-express, so I wonder how this will affect the ratings!
LVL 91

Assisted Solution

nobus earned 25 total points
ID: 17057659
if you foresee a good margin (more than 50 W) you'll be safe !
LVL 70

Accepted Solution

garycase earned 25 total points
ID: 17059018
"... even running 2 cards in SLI i wouldn't expect problems on a 400W+ PSU :) " ==> he's not doing it here, but just so nobody gets the wrong idea from that comment,  running TWO 7950's in SLI would be a VERY bad idea with only 400 watts !!   (400 watts is even marginal for ONE)

Note that the Journey Systems power calculator does NOT have entries for the newest (and power-hungriest) video cards.   nVidia has done a good job with the 7900's -- they actually draw less power than the 7800 series;  but they still draw 85-90 watts (well above any entry in Journey Systems' list).   ... and most folks buying this level of power supply are gamers who WILL run the GPU at max power draw (or even overclock it to higher levels).   Note that the top-end Radeon's draw over 120 watts -- double anything shown in Journey System's video card list (and in SLI mode you'll have TWO of them).

Journey Systems' power calculator is a reasonable "guestimate" IF you factor in a few things:  (1) many newer motherboards have significantly higher base power draws than the 25 watts they use (I'd add 50 watts to their totals to compensate for this);  (2)  be sure and check at least 2 (I'd check 4) of the USB boxes -- EVERYONE will use SOME USB devices eventually;  (3)  check at least 2 hard drives -- every system SHOULD have two (for a variety of reasons);  and it's very likely you will at some point (my systems all have between 2 and 10 hard drives);  (4)  be sure and factor in the correct wattage for your video card -- the Journey Systems' list understates this a lot, as it has not been updated (even the "new" version) to reflect PCI Express cards or the latest video chips.    It's also a good idea to independently compute the voltage requirements on the individual power rails -- your 12v lines in particular can easily exceed the capabilities of your power supply even if the total wattage does not.   There are MAJOR differences in the capabilities and stability of inexpensive power supplies and the top-end units (PC Power & Cooling, SeaSonic, etc.).   Power is perhaps the single most overlooked issue when folks build systems - and unstable power causes more issues than I like to think about.

Having said all that, YOUR system should be fine with 420 watts IF the power supply is a good quality unit.   If you install the 7950GX2 and notice "strange" intermittent problems, however, the first thing I'd do is upgrade to a high-end power supply with a bit more headroom -- something like a 500w Seasonic S12-500  (You can't buy it here, but this is what I'd suggest:

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