How many watts does my psu need to be?

RagBagRover · Dec 10, 2014

Hi, i am planning on upgrading my system and was wondering what psu to buy.

My components are a gigabyte z97 sli
an i5 4690k (which i plan on overclocking)
2 gtx 970's in sli
and i was planning on implementing a custom watercooling loop to cool the 2 970's and the i5
What size psu would be best while keeping the price down - obviously however i would like it to be a reliable and quiet one)

Thanks

Xyos · Dec 10, 2014

800-850W is perfectly fine.

SproutSchon · Dec 10, 2014

Anything above 600W will give you a nice overhead.
Check this website: http://extreme.outervision.com/psucalculatorlite.jsp

With your specs 1 SSD, 2HDDs, 1 optical, 3 case fans, CPU OC 4GHz, 1.5V i got <500W max, 550W recommended.

With a custom water loop you should be fine with a 600-650W PSU.

Xyos · Dec 10, 2014

SproutSchon :

He has 2 970's, 3 drives, and plants to get a cooling loop. 650W is not enough for that.

Please take my advice go for 800-850W.

SproutSchon · Dec 10, 2014

Use the tool and see for yourself.
Without watercooling, his system will never drive more than 500W peak.

Xyos · Dec 10, 2014

SproutSchon :

970 SLI power consumption with DIRECT testing:
http://www.guru3d.com/articles-pages/geforce-gtx-970-sli-review,4.html

Excerpt from Guru3d on 970 sli recommendation:
GeForce GTX 970 or 980 in 2-way SLI - On your average system the cards require you to have an 700~800 Watt power supply unit as minimum.

^ Now add extra drives/watercooling to that. Like I said 850W. Those calculators are false and do not represent real world benchmarks.

williamcummins · Dec 10, 2014

I agree with Xyos on that, 600 watts will be too short. Most power supplies work at their optimal performance around 50 to 80% of full load. Be careful on what psu you buy tho. It's not every 850w psu that is reliable. Since you want to SLI and use watercooling, I'd suggest you get a multi rail psu with generous amount of amperage of each rails.

SproutSchon · Dec 10, 2014

Xyos :

Lol this contradicts your argument.
Measured power consumption GTX 970 2-way SLI

System in IDLE = 123 Watts
System Wattage with GPU in FULL Stress = 439 Watts
Difference (GPU load) = 316 Watts
Add average IDLE wattage ~10 Watts
Subjective obtained GPU power consumption = ~ 326 Watts

This means the whole PC with SLI GTX970 never use more than 439W peak in full stress.

Even if 2 780 will drive more it won't be above 100W.

Xyos · Dec 10, 2014

SproutSchon :

Your were incorrect, I am not here to argue just point out your mistake and give the OP accurate information. Did you read the article and recommendation of Guru3d and the quote I listed? There is no contradiction they explicitly state a minimum of 800W is required for an average system of 2 way SLI. The numbers you are quoting came from a power draw test that occurred at the wall socket, not the actual system usage, and they even state these numbers are not 100% accurate, HENCE THEIR RECOMMENDATION OF 800W MINIMUM FOR SLI.

SproutSchon · Dec 10, 2014

Do you care to explain how wall socket measurements are different than actual system usage?
It is clear you don't know what you are talking about.
The only warning they stated is about the quality of their measurements.

An average system with 2 SLI GTX 780 will have a maximum peak power consumption of 550W-650W that's it.
Their recommendation includes a nice overhead that gives you some breathing room for future upgrades, extreme OC, adding more drives, ...

Look at this link: http://anandtech.com/show/7492/the-geforce-gtx-780-ti-review/15

Max power drawn playing Crysis 3 2 SLI GTX 780: 535W
Max power drawn FurMark benchmark (more demanding than anything you will actually play) 2 SLI GTX 780: 642W
I do agree that my original suggestion was a bit too low but you can have something below 800W that will function very well.

Xyos · Dec 10, 2014

SproutSchon :

"Their recommendation includes a nice overhead that gives you some breathing room for future upgrades, extreme OC, adding more drives, ..."

^The OP has multiple drives, plans to add liquid cooling loops/pumps+the SLI/case fans. See? Do you understand now why I recommended 800+W?

I apologize to you for coming across as rude, but I still disagree with your original post for the reasons I listed.

SproutSchon · Dec 10, 2014

Typically drives fans and watercooling are in tens of W while CPU almost in the hundred of W (150W if you OC like crazy) and GPU couple of hundreds of W.
So basically CPU and GPU will be like 80%-90% of power consumption.
I kept replying because the original arguments were "those calculators aren't trustworthy" and "you need at least 800W-850W" which are incorrect.

The PSU calculator makes everything in your PC run at 90% load which will never happen (you could even set 100% if you really want).
You can even set OC and watercooling.
Therefore it will give an upper limit of power estimation that will never be reached in real life and add 50W overhead on top of that.
This is the way to estimate your power consumption not taking for granted recommendation such as the one provided by the GPU manufacturer.

Xyos :

Don't worry that is fine.
But people do tend to overestimate their needed wattage a lot.
In his case not too much and I agreed in my previous post that my suggestion was maybe a bit too low.
I'd rather see a higher quality, reasonably powerful PSU than a largely overestimated one but with crappy manufacturing.

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