How much power does my PSU need?

  • Thread starter Thread starter Thomas Luzat
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Thomas Luzat

Hello,

I am currently planning to buy a new PC for which I have some trouble
dimensioning my power supply. The components basically are:

-Intel i7 920 (2,66 GHz, but with the option to overclock it to ~3,5 GHz
=> more power)
-Geforce GTX 295
-12 GB DDR3 (6 dimms) @ ~1600
-4 3.5" SATA disks, 7200 rpm
-1 DVD writer

I suppose a Thermaltake ToughPower 750W (~100 €) would do fine, but what
about anything cheaper: 680W, 650W, passive PFC? How do I best calculate
what I require?

Thanks!

Thomas Luzat
 
Thomas said:
Hello,

I am currently planning to buy a new PC for which I have some trouble
dimensioning my power supply. The components basically are:

-Intel i7 920 (2,66 GHz, but with the option to overclock it to ~3,5 GHz
=> more power)
-Geforce GTX 295
-12 GB DDR3 (6 dimms) @ ~1600
-4 3.5" SATA disks, 7200 rpm
-1 DVD writer

I suppose a Thermaltake ToughPower 750W (~100 €) would do fine, but what
about anything cheaper: 680W, 650W, passive PFC? How do I best calculate
what I require?

Thanks!

Thomas Luzat
Click to expand...

Processor TDP = 130W. Times 3.5/2.66 = 171W. Divide by 0.90 to
represent Vcore conversion efficiency of 90%. Gives 190W.

GTX 295 - GPUreview lists it as 289W. No measurement on
Xbitlabs yet.

Four disks - about 50W or less idling. Spinup is 2.5A on 12V
for the motor, or 120W on four drives for the first 10 seconds.
Since graphics and processor are not a max power at that instant,
you don't have to plan for spinup (unless more disks are involved).

Motherboard and RAM. 50W or a bit more.

DVD writer, about 25W writing.

Total 190+289+50+50+25= 604W

You can use a site like newegg.com to get some customer reviews
on power supplies. I couldn't find a review on Jonnyguru for the
Toughpower 750W - maybe I'm having a "bad search day". I'd probably
look for something else.

One picture of the GTX 295 shows it uses a six pin and an eight pin
PCI Express power connector. The picture of a Toughpower I could
find, shows two 2x3 power connectors. Check to make sure you have
the right connectors. There are at least two Toughpower models,
one with modular cabling and one with fixed cabling.

Paul
 
Thomas Luzat said:
Hello,

I am currently planning to buy a new PC for which I have some trouble
dimensioning my power supply. The components basically are:

-Intel i7 920 (2,66 GHz, but with the option to overclock it to ~3,5 GHz
=> more power)
-Geforce GTX 295
-12 GB DDR3 (6 dimms) @ ~1600
-4 3.5" SATA disks, 7200 rpm
-1 DVD writer

I suppose a Thermaltake ToughPower 750W (~100 ?) would do fine, but what
about anything cheaper: 680W, 650W, passive PFC? How do I best calculate
what I require?

Thanks!

Thomas Luzat
Click to expand...

The minimum for your rig is 650W. But that assumes three things:
1) GOOD name brand (no, thermaltake toughpower is not a good name brand)
2) You never want to add another video card (you will be almost maxed out
with just one video card)
3) You are OK with running your power supply at ~80% of maximum rating,
constantly. For a typical 650W power supply, your CPU and video card alone
are going to be pulling ~67% of the available amps from the +12V line. But
that's assuming you were just running a CPU and a video card, which would be
silly. For reliability reasons, you should size your power supply closer to
where you will only be using about 50% of your available +12V rail current.
Or less.

I'd suggest a BFG ES-800. It has four +12V rails, ONE of which (alone) is
more than enough to handle your video card. And it is biased to have more
available power from the +12V rails. So the +12V rail(s) will probably be
running close to 50% or below, which is a good thing. Other than that, you
might try a Corsair 1000HX. Most power supplies won't be able to handle
your rig. You are looking for multiple +12V rails, at least ONE of which
should be 30A or larger. Or, a single +12V rail at 60A or larger. Other
than an oddball 800W (like the ES-800 by BFG), the +12V draw can't be
handled COMFORTABLY by too many power supplies below 1000W. -Dave
 
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