GTX 770 2-way SLI Power Supply Requirements

[BigWhiteKyuubey]

Hello community,
I currently have one MSI GTX 770 2GB.
I plan to purchase another exact same card for a 2-way SLI configuration.
Before I do so, I need to be certain that my power supply unit is compatible with this setup.
I want to ask: What are the exact requirements for the power supply unit? (e.g watts and the amps on a certain rail)

Thanks guys

 

[barto]

The 770 GTX has a TDP of 230 watts which means it can pull a little over 19A on a +12V rail. Two of them in SLI would pull over 38A. Now if you have a PSU with a single +12 V rail, the single rail would need to have at least 38A but actually more because the CPU and a few other components use the +12V rail as well. If you have a PSU with multiple +12V rails, you will need to make sure that each rail has enough Amps per rail and that the total amount of wattage for the +12 isn't exceeded. That means the mulit-rail PSU must be able to supply a wattage in greater than 456 watts.

To sum it up, you're looking for a power supply of at least 700 watts.

Single Rail:

Multiple Rails:

 

[i7Baby]

As a guide, 2x 770's need 850W. See: http://www.realhardtechx.com/index_archivos/Page362.htm. You can calculate it yourself in detail using: http://extreme.outervision.com/psucalculatorlite.jsp. Tryt a good brand PSU: http://whirlpool.net.au/wiki/psu_manufacturers

 

[PCGameFan2]

The Corsair RM750 http://www.amazon.com/gp/product/B00EB7UITQ would have plenty of power to sufficiently supply your system with SLI GTX 770's. You would enough have a enough room to do a little overclocking.

If you go with a quality Gold rated PSU you can easily power your setup. If you went with a less quality Bronze PSU then I would recommend an 850W PSU.

 

[i7Baby]

Check what Wattage you need using a calculator eg - http://extreme.outervision.com/psucalculatorlite.jsp

I think part of the recommendation for using a larger than minimum PSU is so you can also run it as close to the most efficient ~50% power. And also it'll keep temps down and give you a longer PSU life.

 

[barto]

Wattage calculators are garbage. More often then not they are wrong. An 850 watt power supply would be fine, however, my previous statement about a 700 watt power supply is still valid. Power supplies may have one particular load that is the most efficient, but it is completely unnecessary find a power supply that is most efficient at 50% load. Power supplies are designed to be efficient at range of loads. For example, most power supply reviews, test the power supply at 20, 40, 60, 80 and 100% load. It's across all of these loads that are tested. The primary goal for each load is over 80% efficiency.

As seen here: http://www.hardwaresecrets.com/article/Corsair-HX750W-Power-Supply-Review/775/7

That is one of the characteristics of a good power supply. There is very little difference between a power supply with a 4% efficiency difference from 89 to 85 with varying loads. Having the 80+ efficiency at those loads is what matters.

Now, as for how much power is needed. Two 770's may require over 456 watts. The key part is, may. Computer components will only use what they need. As a primary example, my build has a 770, a 3570k OC, a few extra fans, 2 HDDs and 1 SDD. The entire system only pulls 270 watts. That's just a little more than what one 770 can pull fully loaded. Here's a great example of what I'm talking about from AnandTech:

A 7970 has a TDP of 250 watts. There's two 7970s in this review. Just two of the 7970s have a combined TDP of 500 watts. If you add the additional components, (CPU, RAM, motherboard, HD, case fans), the calculation would be safely below 700 watts. Then if you were to find a power supply that did this a 50% load, you're looking at buying a power supply with at least 900 watts! Yet this review shows that the entire system barely pulls the combined TDP of two graphic cards. Do you want head room, yes. It's good to play it safe. I would say add about 20% on top of some hand calculations.

The other important characteristic is the parts that make up the power supply. The power supply needs to remain cool for longevity and efficiency. The Corsair RM750 is one that has cheap capacitors and doesn't have proper cooling. Here is a review of the RM650.
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=363

The top PSU brands are Corsair (TX, HX and AX series), Antec, Seasonic, and XFX.

 

[i7Baby]

Wattage calculators are garbage. More often then not they are wrong. An 850 watt power supply would be fine, however, my previous statement about a 700 watt power supply is still valid.

I'd still play it safe and go with a 850W PSU. I think Calculators are good.

 

[barto]

I'd still play it safe and go with a 850W PSU. I think Calculators are good.

It's not solely about wattage. As I said in my previous post, efficiency and quality components take precedent over wattage. Calculators don't provided that information.

 

[i7Baby]

Yep. Calculators just provide the figure for Wattage that the PSU has to supply. Forums and reviews will provide info on wht is a good PSU that can supply that Wattage.

 

[PCGameFan2]

I'd still play it safe and go with a 850W PSU. I think Calculators are good.

It's not solely about wattage. As I said in my previous post, efficiency and quality components take precedent over wattage. Calculators don't provided that information.

Exactly, the RM 750 I recommended is plenty and perfect for what you need.

 

[barto]

Did you guys even read what I posted?

Sigh. Why bother...

OP, best of luck.

 

[Cace Roree]

i know this post is waaaaaaay old now. but id like to ask you guys a question.. i kind of having the same dilema as the op.. but.. i already have my psu.. i have a ax760 platinum psu from corsair.. i have a 6300 and a gtx 770.. if i add another 770 would the psu be able to handle it? even if i oc my fx 6300 to 4.3-4.5? thanks in advance..

 

[i7Baby]

It'd be a bit on the lean side. They are good psu's, but I'd like to have more headroom.

 

[Cace Roree]

thanks

 

[barto]

You'll be fine. The AX is an awesome, very efficient PSU. You won't have any issues running SLI 770s.

 

[gchow03]

You'll be fine. The AX is an awesome, very efficient PSU. You won't have any issues running SLI 770s.

Hello Barto. I am very interested in your responses.

I am currently running a Seasonic 660W Plat. on my rig.
My PSU can generate 55A for +12V rail.

I have a i7 3770k not OC yet. (plan to maybe in the next few years).
2x4GB ADATA DDR3 - 1600MHz
Intel SSD 530 Series 240GB
3x HDD 1 2 at 7200RPM, 1x 5400RPM
ASUS GTX 770
and a lot of case fan cooler.
I use a Nauc.(something like that) fan cooler thats like as big as my PSU as a CPU Cooler.

Please let me know. I like your response where Quality takes place instead of just sheer Wattage.
But i m hesitant if I can support 2x GTX 770 SLi.

 

[i7Baby]

Seasonic don't make a 660. They make lots of 620's and now 650's. You should have 850W to run a pc with 2 x 770's per real hard tech.

 

[gchow03]

Seasonic don't make a 660. They make lots of 620's and now 650's. You should have 850W to run a pc with 2 x 770's per real hard tech.

Uhm... Unless my eyes are playing tricks on me: http://www.newegg.com/Product/Product.aspx?Item=N82E16817151121

Is this not by Seasonic? :/

 

[barto]

You can stop rubbing your eyes. That would be a Seasonic.

Is it possible, yes. Would I do it? Eh, probably not. Sub 700 watts is something to be cautious about. Two 770s is 40 watts alone. Just the two cards would put a 72% load on the PSU. That's a little high considering no other components are added in. Higher loads wear on the power supplies faster thus shortening their lives.

I would honestly pass on this one. If you are really heart broken about this, try and sell the PSU for a replacement with higher wattage.

 

[Shawn Lemon]

The 770 GTX has a TDP of 230 watts which means it can pull a little over 19A on a +12V rail. Two of them in SLI would pull over 38A. Now if you have a PSU with a single +12 V rail, the single rail would need to have at least 38A but actually more because the CPU and a few other components use the +12V rail as well. If you have a PSU with multiple +12V rails, you will need to make sure that each rail has enough Amps per rail and that the total amount of wattage for the +12 isn't exceeded. That means the mulit-rail PSU must be able to supply a wattage in greater than 456 watts.

To sum it up, you're looking for a power supply of at least 700 watts.

I have a 635W PSU with a single 12V rail that is 45A, 536W. I'm not sure if I can add another GTX 770 but I'm going to try and upgrade if I can't. Do you think I will need a new PSU?

 

[barto]

I have a 635W PSU with a single 12V rail that is 45A, 536W. I'm not sure if I can add another GTX 770 but I'm going to try and upgrade if I can't. Do you think I will need a new PSU?

A quick search for a 635 watt PSU gave me a Sigma Shark and a Raidmax. I wouldn't even try a second GPU with either of those. Like in my previous posts, I wouldn't recommended a power supply sub 700 watts. Definitely if the not if the PSU is a Sigma or Raidmax.