Choosing the right size of PSU!

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Posts: 488
Joined: Fri Aug 09, 2013 4:31 pm
Location: Denmark

Sun Feb 23, 2014 9:40 am

First watch this video (Thanks Ahven1)
Apart from his gaffe around 2:05 (Getting the effiency explanation wrong) his results are valid and perhaps a little surprising for system builders..

The reason for wanting a 80+ rated PSU is that on a non-80+ PSU you might typically have 65-75% efficiency. This means while the PSU is rated for eg. 500W, when it delivers those 500W, it'll draw (500/0.75) = 666W from the power socket. That's 166W turned into heat right there!
If you game eg. 20hrs a week (or ~1000hrs a year) that would be 166kWh wasted..
If you had used eg. 80+ Silver (85% efficiency @ 100% load), you would only have wasted 88kWh.

80+ rated PSU's have atleast 80% efficiency and obviously the metal ratings means better efficiency Titanium > Platinum > Gold > Silver > Bronze > "White". Titanium


Depending on how long you plan using yor PSU for, remember that it will also slowly decrease in power output capacity over the years.. if you're looking at using it for eg. 5 years, you will only be getting ~80% out of a PSU compared to when it was new (in a somewhat bad scenario, with less degradation over time by more expensive PSU's as they DO use better components, most of the time).

If you watched the YT vid, you'll ask yourself how much power will MY system need? His setup was pretty great - OC'd 4770K, OC'd GTX680, watercooling loop, 1 SSD, 2HDD's, 11 Fans, 2 LED strips (and a partridge in a peartree!) and yet maxload was ~360W from the power socket.
As he stated he had a 750W 80+ GOLD PSU, we can use the table and find that the PSU worked at 90% efficiency and so the system only demanded 324W all in all (and 36W was turned into heat in the PSU).

If you look at the max power rating of the i7-4770K, it states 84W, the 680GTX says 195W = 279W total. If you then add in the mobo, watercooling, fans & hdd (ssd's draw VERY little power) - you get to the 324W total.

So basically, JayzTwoCents could add 2 more 680GTX's and that would still be possible to run from his 750W PSU - even though he'd have to take care and pray that the PSU output didn't degrade too much!

Links to Power Req Calcs ... orlite.jsp

Use the above as a guideline - and use common sense aswell :)

As a FINAL comment - if you look at the 80+ graphic, you'll see that most PSU's have better efficiency around the 40-75% load capacity and while 80+ Silver/Gold n upwards PSU's aren't cheap, having a little extra means you'll put your PSU efficiency in a better position!

TL;DR - Unless you're doing Triple/Quad SLI/Xfire (or experimenting with voltmodding/hardcore OC) - don't buy more than 800W!!
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Posts: 10
Joined: Tue Feb 25, 2014 4:10 pm

Wed Feb 26, 2014 12:12 pm

Nice, thanks for sharing! I have a lot to learn lmao. Wish I could be hands on.
Posts: 57
Joined: Sun Apr 27, 2014 1:35 pm
Location: Azeroth

Mon Apr 28, 2014 2:47 pm

Oh great information! Very helpful :)
Posts: 37
Joined: Thu May 15, 2014 7:05 pm
Location: Edmonton, Canada

Sun May 25, 2014 5:58 pm

True story.
  • CPU: Intel i7 - 4770k @ 3.9Ghz
  • Motherboard: Asus Maximus VI Extreme
  • RAM: 16Gb 2100Mhz
  • GPU: 2 Yes, I said 2 EVGA 780ti SC 3Gb SLI
  • SSD: 1 240gb for Windows 7, 1 500gb for steam games, 1 120gb for beta testing games.
  • HDD: Seagate 1TB for everything else
  • PSU: EVGA 1000w G2 Supernova
  • Case: Mid Velocity 14 bays, 3 hotswappable locations
  • Monitor: 2 ASUS VE278Q 27" and 1 Samsung 21" 1080 LED TV
Posts: 3
Joined: Sun Jan 18, 2015 7:36 pm

Sat Jan 24, 2015 2:12 pm

So my 1300 watt psu's are overkill? :eek:
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