How Much Do You NEED?

[BoomerD]

Most of us buy a far bigger PSU than our systems demand. Myself, I usually advise to buy a unit that has at least 20% more capacity than the system should need, if only because I don't like to push things to the max, PLUS, it gives a bit of room for overclocking.

HOWEVER, I decided to put the Kill-a-Watt on my new build, and the results surprised me.

The specs of my rig:
CoolerMaster HAF 932 case with the stock fans
ASUS P7P55D-E Pro motherboard
i5-760 Processor
Noctua NH-U12P SE2 CPU cooler with both fans in push/pull
EVGA GTX 460 1 Gb Superclocked Card (1373AR)
4 x 2 Gb Corsair XMS RAM running in XMP 1600 MHz mode
1 Samsung SATA DVD burner
1 Samsung IDE DVD Burner

With stock clocks on the processor, this rig draws surprisingly little wattage:
after everything loads following boot sequence..maxed during load at 201, then dropped to 102, settled in at 94-96 watts at idle
Running Furmark @ 1024x768 in Extreme Burning mode: 300 to 310 watts. (310 with GPU fan at 100% for testing)

With the processor overclocked to 3534 MHz,:
Idle 140 watts, (maxed at 230 during boot & load process)
Furmark 1024x768 Extreme Burning Mode: 340 to 352 watts (GPU fan @ 100% for testing)

I know I can push the processor a bit farther by modifying the CPU voltages...something I'm always hesitant to mess with, but this testing shows that I have PLENTY of room with my Corsair HX620 to do so should I decide to try that.

I don't have any "current " games to test with, but BF2 with everything set at max including 8X AA only drew the system to a max of 225 watts. (overclocked)

When you calculate how much your system needs...remember, the PSU calculators aren't very accurate when compared to the real-life draws of your system.

Using the eXtreme PSU calculator which is considered to be pretty accurate, I get the following:

Minimum PSU Wattage: 387 W
Recommended PSU Wattage: 437 W
(which isn't too far off)

http://www.extreme.outervision.com/psucalculatorlite.jsp


Edited typos

 

[Blain]

I buy quality power supplies and plan on keeping them through several upgrades.
So I always buy more capacity than I actually need.
Not for OCing or anything like that, but for aging and to tune PS for peak efficiency at about 50% capacity.
Most reviews I've read indicate that peak power supply efficiency kicks in around that 50% point.

 

[BoomerD]

I buy quality power supplies and plan on keeping them through several upgrades.
So I always buy more capacity than I actually need.
Not for OCing or anything like that, but for aging and to tune PS for peak efficiency at about 50% capacity.
Most reviews I've read indicate that peak power supply efficiency kicks in around that 50% point.

Agreed. According to the Jonny Guru review of this PSU, it should be at about 83% efficiency with this load.

 

[IGemini]

For my build the calculator puts it at around 350-400W. That's the sig config with 100% load (which happens a lot, since I'm crunching F@H and Rosetta@H on this machine when I'm not using it) and assuming every device I would use is connected. Pushes above the 50% margin of my 650TX under load but it stays around 80-83% efficiency regardless. Not quite sure what its real power usage is yet, a KaW meter is one of the next things on my buy list.

The topic reminds me of one of AT's older benchmarks looking at 3-way SLI of 8800 Ultras, which were beasts as far as power consumption goes. The whole setup pulled 730W from the wall under load. Jesus. "No, not even Jesus needs this much power." Power efficiency has come a ways since then.

 

[BoomerD]

My old build, (P4 3.06 with a VisionTek AGP X850XT PE, 3 Gb PC3200 RAM) idled at about 170 watts and maxed at a bit more than 300 watts with the same Kill-a-Watt.

 

[Aristotelian]

I just used that calculator and (without overclocking in consideration) it said that my approximate draw will be 715W or so, recommending a 750W PSU.

If I plan to overclock a 2600K and 2x 580s, would a quality 850W like the Seasonic x-850 be sufficient? The next jump up to gold psus seems to be around 1200W - overkill? I might add a third 580 at some point, but definitely not now. I do want overclocking headroom.

 

[ZipSpeed]

There are lots of people running overclocked i7s and 580 SLI on quality 850W with no issues.

 

[Aristotelian]

There are lots of people running overclocked i7s and 580 SLI on quality 850W with no issues.

Thanks, ZipSpeed!

 

[Yellowbeard]

When you calculate how much your system needs...remember, the PSU calculators aren't very accurate when compared to the real-life draws of your system.

I think THIS is pretty helpful for selecting a PSU. I wrote it around our PSUs but it applies to any brand of course.

 

[BoomerD]

I think THIS is pretty helpful for selecting a PSU. I wrote it around our PSUs but it applies to any brand of course.

I agree. The Corsair calculator is pretty good...but biased It ONLY recommends Corsair units!! :biggrin:

 

[dualsmp]

My old build, (P4 3.06 with a VisionTek AGP X850XT PE, 3 Gb PC3200 RAM) idled at about 170 watts and maxed at a bit more than 300 watts with the same Kill-a-Watt.

My old P4 is the reason I bought a killawatt since I read that P4 class machines were power hogs. When I hooked up the killawatt it was 90w idle and around 180w load (P4 2.6Ghz@3.1 Northwood C, Nvidia 4200Ti, 2 GB DDR). Turned out not to be the power hog I thought it was. I think the Prescott P4's brought on the reputation of P4's being space heaters.

Later when I passed the P4 on to my dad I was able to parse it down to 63 watts idle and around 150w load by swapping out the video card for ATI 9600XT.

Most people would blush to see how little power their computer really uses. A nice quality 300w or 350w PSU will power most mid-range PC's easily.

 

[beginner99]

Most people would blush to see how little power their computer really uses. A nice quality 300w or 350w PSU will power most mid-range PC's easily.

probably true but it runs hotter than a 500w at same load meaning more fan noise. And then I rather have some headroom, because once you run into troubles you can at least exclude the chance that your psu is not powerful enough. And you normally keep it for more than 1 build so you never know what the next will do.

Yes, I'm justifying buying an too strong psu (700w) but then there was a nice review here about it and the lower wattage models where actually about the same or even less efficient at around 200w -300w.
Mine supposedly is around 90% efficient at that wattage. So the only downside was a slightly higher price.

(I run seti and milkyway@home) so I'm rarely on idle wattage levels)

 

[dualsmp]

probably true but it runs hotter than a 500w at same load meaning more fan noise. And then I rather have some headroom, because once you run into troubles you can at least exclude the chance that your psu is not powerful enough. And you normally keep it for more than 1 build so you never know what the next will do.

Yes, I'm justifying buying an too strong psu (700w) but then there was a nice review here about it and the lower wattage models where actually about the same or even less efficient at around 200w -300w.
Mine supposedly is around 90% efficient at that wattage. So the only downside was a slightly higher price.

(I run seti and milkyway@home) so I'm rarely on idle wattage levels)

Your situation is a bit out of the norm though. Most PC's sit at near idle or idle most of the time. If your loading your PC 24/7 it would make sense to buy a PSU that is a bit oversized to use about 50% of the PSU's total capacity since PSU's tend to have their highest efficiency at 50%. Sometimes it does make sense to go big (but not too big ).

 

[PreferLinux]

My old P4 is the reason I bought a killawatt since I read that P4 class machines were power hogs. When I hooked up the killawatt it was 90w idle and around 180w load (P4 2.6Ghz@3.1 Northwood C, Nvidia 4200Ti, 2 GB DDR). Turned out not to be the power hog I thought it was. I think the Prescott P4's brought on the reputation of P4's being space heaters.

Later when I passed the P4 on to my dad I was able to parse it down to 63 watts idle and around 150w load by swapping out the video card for ATI 9600XT.

Most people would blush to see how little power their computer really uses. A nice quality 300w or 350w PSU will power most mid-range PC's easily.

My P4 541 (Prescott, HT, 3.2 GHz) with a GeForce 8400GS uses about 100-120 W at a reasonably high load (AVG doing a fast scan, Windows Experience Index refreshing its score, 7Zip benchmark running, playing SuperTuxKart). Can't remember the idle load. I have a Antec Earthwatts 500W 80+ PSU.

 

[Meghan54]

Most people would blush to see how little power their computer really uses. A nice quality 300w or 350w PSU will power most mid-range PC's easily.

LOL! That mentioned 300W ps would just barely get my pc to function at idle.....it pulls 300W from the wall at idle and has pulled 600W during OCCT testing.

 

[JEDIYoda]

Most people would blush to see how little power their computer really uses. A nice quality 300w or 350w PSU will power most mid-range PC's easily.

That`s not true at all!! these days a 300 - 350 watt PSU would run very hot and might not be very efficient! I`m sure you can rebut what I am saying, but some of us have high end computers with highend video cards etc.....

 

[Soundmanred]

That`s not true at all!! these days a 300 - 350 watt PSU would run very hot and might not be very efficient! I`m sure you can rebut what I am saying, but some of us have high end computers with highend video cards etc.....

"mid-range PC's"

 

[Concillian]

probably true but it runs hotter than a 500w at same load meaning more fan noise.

Heat is a function of efficiency. It's easy enough to buy based on efficiency certification if you're concerned about heat. Those 250W Dell 80+ silver PSUs from eBay are fine for the average computer, though probably not for the average AT reader.

I survived just fine for 5+ years on a 380W PSU, even overclocking CPU and video card. The point of the thread is that when you measure what you actually use, it's much lower than most estimates.

Even people doing folding / seti ... they're not fully loading both the CPU and GPU. Either they're using GPU or CPU. Gaming doesn't max both either. There's some leeway in most cases. The highest draw I measured on my machine with a Kill-a-Watt is much lower than I expected based on TDPs. And in-game power draw is WAY lower than testing with Furmark.

 

[dualsmp]

LOL! That mentioned 300W ps would just barely get my pc to function at idle.....it pulls 300W from the wall at idle and has pulled 600W during OCCT testing.

And you would consider your rig mid-range? Don't you have an overclocked i7?

 

[Meghan54]

And you would consider your rig mid-range? Don't you have an overclocked i7?

Yes, just an i7 920 with a 4870 video card presently.....watecooled with dual DDC2 pumps.

Definitely mid-range. Upper end.....look to Agio's setups. He's upper end, completely.

 

[Concillian]

I think what we have here is a failure to communicate.

I think Meg has a very different definition of "high end computer" than most people if a watercooled and significantly overclocked & overvolted i7-920 doesn't fit into the definition of "high end computer".

If a watercooled OC'ed OV'd i7 1366 is considered midrange, what's the cutoff for low-end? Anything less than a stock i7-920?

 

[venomous41]

will a ocz 750 run 2x5870's with a midrange system?

 

[venomous41]

its doing it now, with just one 5870. but looking to add another.

 

[beginner99]

Even people doing folding / seti ... they're not fully loading both the CPU and GPU. Either they're using GPU or CPU.

wrong. I run seti (CPU) and milkyway(GPU). Seti uses 100% of cpu. It's pretty intense especially with HT on which does make a pretty huge difference. Not sure about the gpu but gpu scores like 100x times more points than cpu.

 

[Yellowbeard]

I agree. The Corsair calculator is pretty good...but biased It ONLY recommends Corsair units!! :biggrin:

LOL....I'll check into that