"Right sizing" my PSU

[cubsfan-budman]

Heya gang,

So, I'd like to get a new GOLD rated power supply as I'm doing several upgrades to my computer.

My future state:
Intel i2500K @ 4.5ghz
ASUS P8Z68-V Pro Gen 3
EVGA 780
Samsung 840 SSD

My intuition suggests that a 650w PSU would probably do the job.

Here's what I *think* I should do, and I wonder if you experts would validate:

Get all my stuff together and plug it into a Kill a Watt. Prime95 that bitch to find out what it draws under load (will this load the GPU?).

Take that number and divide it by, say, 500, 550, 650, 750 etc to find out what percentage of the PSU will be used by my stuff.

Find a PSU where you fall into the 50-70% range for usage, so that you make the "most" of the PSU's efficiency band.

What do you think? Am I on the right track?

Thanks!!

C

 

[Silverking]

No prime95 stresses your cpu. FurMark stresses your GPU. Check out video card reviews where they state their testing setup and see what programs are being used and how. Also using the Kill-a-watt is a little misleading as you are looking at the AC current that comes out of the wall and there is always a loss during conversion to DC inside the power supply.

 

[Parja]

No prime95 stresses your cpu. FurMark stresses your GPU. Check out video card reviews where they state their testing setup and see what programs are being used and how.

Correct. You're probably best off running some kind of gaming benchmark or just playing a demanding game to get a good reading of your system loaded up.

Also using the Kill-a-watt is a little misleading as you are looking at the AC current that comes out of the wall and there is always a loss during conversion to DC inside the power supply.

Right, but he should be able to determine a rough efficiency level of his power supply for the load he's pulling.

For the system you've specified, I'd personally go with a 650W power supply. You'll be in the efficiency sweet spot at full load and it gives you a fair amount of headroom if you decide to add some stuff to it in the future.

If you think you ever plan on adding a second video card, I'd probably shoot for something around 850W.

 

[cubsfan-budman]

Thanks for the advice, guys.

 

[bigsnyder]

A good quality 550w will be more than enough. Look at the power draw figures in the GPU reviews right here on HardOCP. Bottom line, get whatever you can find the best deal on. Most single 780 rigs pull in a little north of 400W with overclocking. If you plan to add a second 780 then get at least 750w.

As far as the kilowatt experiment, here are my results:

System:
Asus Z87-A
i5 4670k @ 4.3Ghz
2 x 4GB DDR3 1600
Asus DurectCU II 780 OC Boost-1100/Memory-6800
128GB Samsung 830
2 x 1TB Western Digital Blue -RAID 0
LG Blu-Ray/HD-DVD Combo Drive
Soundblaster X-Fi ExtremeMusic
Seasonic G 550w

After cranking Furmark up (2560x1440) and running Prime95 on two cores (running all 4 bottlenecks GPU), I barely broke 400W