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General PSU questions

post #1 of 24
Thread Starter 
I'm trying to figure out a bit about how PSU's work in an effort to get a near silent system, even under load.

Big question, is lets say I need 400W under load. If I get a 500W PSU, does that mean the PSU is running at 80%? And if I had an 1000W PSU (just hypothetical numbers) it would be at 40%?

Wouldn't the PSU running at 40% then be much quieter because it has to work less? And therefore if I want a silent system, the bigger the PSU the quieter?

I'm definitely no expert here so I may have this all wrong, but would appreciate an explanation that may help me find a PSU that will be quiet under full load in my sig rig (plus a couple HDD and fans).
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post #2 of 24
Yes that is correct, a PSU made to withstand higher wattages copes with smaller wattages more effortlessly than a power supply of lower capacity. Also consider the 80plus standard, it shows whether or not a PSU is supplying an accurate and efficient amount of power.
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post #3 of 24
Thread Starter 
Huh, good to know. So if bigger is better (better being quieter and high quality of course), I wonder why there is an Overkill PSU thread.

I wonder if an 850 would be much quieter?
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post #4 of 24
Quote:
Originally Posted by nicros View Post
Huh, good to know. So if bigger is better (better being quieter and high quality of course), I wonder why there is an Overkill PSU thread.

I wonder if an 850 would be much quieter?
Is this for your sig rig?
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post #5 of 24
Quote:
Originally Posted by nicros View Post
Huh, good to know. So if bigger is better (better being quieter and high quality of course), I wonder why there is an Overkill PSU thread.

I wonder if an 850 would be much quieter?
Sorry, he's given you bad info. There's a lot of that among people who don't understand power supplies.


The only thing in a power supply that should make noise is the fan (inductors can whine, capacitors can squeal, etc, but they aren't supposed to). The higher quality the fan, the quieter. The slower the fan spins, the quieter.

Given a 650W and 850W power supply from the same series, at any given load they still need to exhaust the same amount of heat. So the fan will spin at the same speed (approximately).

So to get a quieter power supply, you need to find one with a higher quality fan. In addition, a more efficient power supply will have less heat to exhaust, so they can program the fan controller to be less aggressive. That means lower RPM, so a quieter fan.



So if you want a quieter PC, get a higher quality power supply with higher efficiency and a better fan. Some 80PLUS Gold power supplies may even have the fan turn off at low loads, or even omit the fan entirely--see the SeaSonic X series.



Wasting money on getting a 1kW power supply is simply idiotic.
post #6 of 24
Bigger is better, within limits. Efficiency on a PSU is on a curve, it peaks at 60-80% load, either side of that peak, it drops off. But if you stay within the 40-100% area, then it's not a huge drop. Buy yourself a 1kw PSU for a 400w load, and when the rig is idling, then you drop into the sub 20% load area where efficiency just plain sucks on most units.

Plus of course, there's the financial aspect, buying a huge PSU is really pointless, you'd be throwing money away for nothing. Sure a modicum of overkill is entirely reasonable, if it won't cost you much money. I paid the extra 10 pounds for the 850w unit when I could have bought the 750 (I mainly swapped for modular and more PCI-E cabling). I'm happily in the modest overkill league, because I was buying a new unit anyway.
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post #7 of 24
why fear when Phaedrus2129 is here!!!
post #8 of 24
Thread Starter 
Quote:
Originally Posted by TwoCables View Post
Is this for your sig rig?
Yep! Under full load (playing Crysis2 for example), my PSU is by far the noisiest part of my system.
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post #9 of 24
Quote:
Originally Posted by nicros View Post
Yep! Under full load (playing Crysis2 for example), my PSU is by far the noisiest part of my system.
Is it a ToughPower unit? I'd be surprised if it is, but I'm still curious. If it's not a ToughPower, then does it have "TR2" on the label? I mean if it's a TR2 unit, then I'm not surprised.
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i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
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250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
KeyboardPowerCaseMouse
Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
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It's a computer!
(19 items)
 
  
CPUMotherboardGraphicsRAM
i5-2500K @ 4.5GHz (1.368-1.384V fixed voltage) ASUS P8P67 EVO B3 (UEFI ver. 1850) GTX 780 ASUS DirectCU II (1228 / 6300, 1.180V) G.SKILL Ripjaws X 8GB (2 x 4GB) 1866MHz, CL9 
Hard DriveHard DriveHard DriveOptical Drive
250 GB Samsung 840 EVO (C:\) 250 GB Samsung 840 EVO (D:\) 150 GB WD VelociRaptor Samsung SH-S243N 24x DVD Burner 
Optical DriveCoolingOSMonitor
Samsung SH-S203N 20X DVD Burner Thermaltake Frio Win 7 Home Premium x64 SP1 Retail AOC G2460PG (24" 1920 x 1080 144Hz G-SYNC) 
KeyboardPowerCaseMouse
Filco Majestouch 104-key Cherry MX Blues w/NKRO Corsair HX650 (Bronze, ordered on 12-12-2009) CM 690 Intellimouse Optical (1.1A) 1000Hz polling rate 
Mouse PadAudioAudio
Basic, but premium round X-Fi Titanium HD Klipsch ProMedia 2.1 (with 16 AWG Monster Cable... 
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post #10 of 24
Thread Starter 
Quote:
Originally Posted by Phaedrus2129 View Post
see the SeaSonic X series.
Is this what you would recommend? Which one if I might ask?
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