How Accurate is "Extreme Outervision" Calculator?

[BonzaiDuck]

Every time I've built a system, I ran the numbers on Extreme Outervision.

I played it safe and ordered a PSU matching the result.

Lately, though, I've seen opinions that diminish the need for high-wattage PSUs. These opinions obviously involve a discussion of graphics cards -- even 2x SLI.

Now I'm pondering the possibility of ordering a second graphics card for SLI. I ran the numbers in E-O, and I come up with 757W. This is mildly padded with an extra PCI/E card and HDD, and cautious estimates of capacitor aging.

I can see how my system at near-idle is using about 90W. Running a game with the single gfx card pushes power-consumption (measured through UPS monitoring software) to about 260W. Only some of the increase would be due to the gfx card: the system is overclocked and shows about 140W package power for the CPU at full load.

So suppose I assume that this CPU overhead doesn't exist? Instead, I assume (falsely, needlessly) that the second gfx card adds a full 170W to the total? This would be about 430W total.

So what's with "Extreme Outervision?" I'm beginning to suspect -- since I always try to buy top-performing/top-rated PSUs (Seasonic) -- that I've been buying more PSU than I need for several years.

 

[TemjinGold]

If you are talking about 2 780s (since that's the card you have below), then that 757w recommendation is about right.

 

[BonzaiDuck]

If you are talking about 2 780s (since that's the card you have below), then that 757w recommendation is about right.

Actually, I threw in GTX 970 data. There is this "storm" raging over 500MB of VRAM, but I wanted to see how the numbers looked. And I know the 970 uses less power than the 780 . . .

 

[lehtv]

Well, what does it say with 780 SLI?

 

[Berliner]

Running a game with the single gfx card pushes power-consumption (measured through UPS monitoring software) to about 260W.

If you trust your measurements, there should be no problem adding the second card.

I would, however, make sure that the card was actually put to max load. Games can easily be CPU limited.

 

[BonzaiDuck]

If you trust your measurements, there should be no problem adding the second card.

I would, however, make sure that the card was actually put to max load. Games can easily be CPU limited.

You're right. I have to trust it before anybody -- it's my estimate, my parts -- my wallet.

Consider the "method." I collect extant data -- so I find at the spec tab of the Egg item-display page for the card -- that the Power requirement is " : 145W . . " This could also be had at MSI's site and spec page. I therefore assume that is the non-overclocked spec peak or load power consumption of the card.

I want to know the over-clocked wattage of two cards at load, and I want to know the total for my system under maximum possible load. I know that at idle, the system with the stock graphics card at idle is between 80 and 90W-- so call it 90. I know that there is some power-consumption of the card as component of that 90; if I ignore subtracting it out -- call the base wattage 90 at idle. This means that the idle graphics card is going to get counted double anyway, since I use the spec peak wattage as the estimate. So I have a "bias of caution" in my method.

The CPU is also overclocked; it's wattage at maximum peak/load is about 140W. If I don't take the ~14 to 18W of the processor at idle out of that, I have another cautionary bias.

The graphics cards seem to overclock to review-recommended speeds with a 0.05V bump in voltage, something across a range like 1.20+ and 1.25+V. There is a 110% ceiling on power-consumption with these cards, at which level they throttle back. So figure 145W + ~15W is overclocked peak wattage.

Now:

90W system idle
+ 140W with CPU at peak load
+ 320W @ 160W each card
===============
<= 550W

I think a person would be just fine with a 550W PSU, Sandy, Ivy or Haswell to non-LN2 overclocking, fully stable average limits. Of course, my base power consumption includes only SSD + HDD, one DVD/RW, two LED fans, one hi-performance fan and slightly less of a 120mm for 4 fans. Probably within generally accepted "sane" voltage. I'm guessing 1.38V for SB, 1.31 to 1.33V for IB, and maybe 1.30V for Haswell. I exclude the E processors -- figure it out. First priority -- what's the expected sustained overclock peak wattage?

So I'm rocking a Seasonic 650W -- "partly modular," it was either Gold or Platinum. It's about 3 months old -- less in actual hours running.

I'm trying to imagine how or when I'd want a bigger PSU. I even think there's plenty of extra headroom.