620w max PSU ok for GTX 660 SLI?

pieguyx1000 · Mar 11, 2013

Ok, so I have a 620 watt PSU, it is a SeaSonic S12II 620W. I read some reviews on it and it seems to be of good quality. It says it can do 620 watts max, so I'm not sure if it can do GTX 660 SLI. I've read online that the GTX 660 needs at least 24 amps on the +12v rail, and this power supply says it has 2, each with 24 amps for a total of 48 amps on the +12v rail. Right now I have one EVGA GTX 660 FTW Signature 2 and everything is working fine. If I do SLI I'm going to buy another of the exact same type so I don't really know if it matters. Right now I have a pretty light system with only 1 HDD, an overclocked I5 3570K, a blu ray drive, about 2 140mm and 4 120mm fans. All the other details should be in my signature. Does my overclock affect if I can do SLI? If I do SLI I won't be overclocking the GPU, so that doesn't need to accounted for. Also does it matter if I might add an SSD in the future?
Thanks!

completelyrandomname · Mar 11, 2013

It should be more than enough since they don't use much power anyways.

pieguyx1000 · Mar 11, 2013

So I just went to an online PSU calculator, and It entered my specs, and it recommended
Minimum PSU Wattage: 575 W
Recommended PSU Wattage: 625 W

Does it matter that it's 620 watts max? Is there any chance this could kill my system running that close to it's max? Will this reduce my PSU's lifespan? Sorry for all the little questions, it's just that this is my first time SLIing, and I don't want to make a big mistake.
Thanks

bgunner · Mar 11, 2013

FYI SSD's use around 3W max verses a HDD 4W idle -10W maximum for full activity. One of the SSD's selling points is low power consumption.

5W will not make a difference in this case. I usually recommend a 750W PSU if some one says "I want to SLI/Crossfire", of course this depends on the GPU also.

pieguyx1000 · Mar 11, 2013

Does my overclock to 4.5ghz change anything? When I did the online PSU calculator, I set my i5 as 3400mhz @ 1.15 v OCed to 4500mhz at 1.28v. It seemed to make a big difference. Also Does PSU aging matter? I set it at 20%.
I'm using this PSU calculator:

http://www.extreme.outervision.com/PSUEngine

jnkweaver · Mar 11, 2013

pieguyx1000 :

Don't Panic! (Adams B-day) The online calculator you used was wrong. It must be doubling everything for draw. Your system will run 300-400 max. You bought the best brand psu in my opinion and with 620W you will be right in the midst of the best efficiency (usually around 50% load). The Seasonic supply will last years. Good choice!

bigcyco1 · Mar 11, 2013

Here is Guru3Ds power supply recommendation:

GeForce GTX 660 - On your average system the card requires you to have a 450~500 Watt power supply unit.
GeForce GTX 660 SLI - On your average system the cards require you to have a 700 Watt power supply unit as minimum.

If you are going to overclock GPU or processor, then we do recommend you purchase something with some more stamina. http://www.guru3d.com/articles_pages/msi_geforce_gtx_660_twinfrozr_iii_review,7.html

jnkweaver · Mar 11, 2013

Ok I totally missed the SLI comment in the intial post.

If you plan to SLI soon and keep the current supply then I would go with a 750-850W range.

On Newegg the Gold low cost winner is the Rosewill Capstone. I would only recommend the Capstone series (made by Super Flower) for Rosewill 750W $112 after shipping http://www.newegg.com/Product/Product.aspx?Item=N82E16817182073

The XFX (made by Seasonic) is fully modular 750w $120 after $20 MIR http://www.newegg.com/Product/Product.aspx?Item=N82E16817207029

The XFX 850W is fully modular and $130 after $15 MIR http://www.newegg.com/Product/Product.aspx?Item=N82E16817207028

Out of these 3 I would go with the last one.

pieguyx1000 · Mar 12, 2013

I just to be thinking about this the right way. If I SLI two GTX 660's they will draw an absolute max of 300 watts because they only have one six pin power connector and the 75 watts from the actual PCI port itself. Wouldn't that leave a little less than 300 watts for everything else. Even if I say that the CPU uses 150 watts. that still leaves 150 watts for an HDD. a few fans, and the motherboard itself. I know I'm overcomplicating this. At this point I just want to learn about this. Does my math hold true in this situation?

djangoringo · Mar 12, 2013

You're fine with that psu, it's a quality one, and two 660 gtx won't draw more than 280W, maximum tdp of each is 140W, you still have a lot of room in there, your system won't pull more than ~450W-500W(estimated) with the rest of the stuff(this is including the two 660 gtx) at load, that leaves you still with a decent margin, you be under or about 80% load of the total of the psu(this is when at full load), which still gets good efficiency and it's acceptable.
In short, you're fine with that psu for two 660 gtx.

bgunner · Mar 12, 2013

The thermal design power (TDP), sometimes called thermal design point, refers to the maximum amount of power the cooling system in a computer is required to dissipate. This does not mean that it is the max the part will draw.

djangoringo · Mar 12, 2013

Yes, actually it's a bit less than that, it's what the nvidia says for maximum, the 660 gtx has only a 6 pin pcie connector i don't see it sucking it more than 140W.
Let's see an e.g. like the high oc card from factory like the 660 gtx msi hawk : http://tpucdn.com/reviews/MSI/GTX_660_HAWK/images/power_peak.gif

pieguyx1000 · Mar 12, 2013

I collected these measurements directly from the wall socket with a 'Kill A Watt' from P3
The measurement came from the computer with the exact specs in my signature. The only thing connected to it were a mouse, keyboard, and a DVI connection outputting to my monitor. I believe I did two tests with each program combination, one with 'normal' fan speed, and another with max fan speed. I didn't really know how much of an impact fan speed would have, so that's why I did it.

Idle wattage: about 75W
Max fans: about 78 w

Only prime95 real temp and asus ai suite open
Prime95 wattage: 150 to 160 max:167
Prime95 wattage with max fans: 155 to 165 max:166

OCCT power supply test.
GPU-z open
Settings 1600x900
Gtx 660
Normal fans
Wattage:270 to 280W max: 285W
Fans max wattage: 275 to 282W max: 290W
When I clicked out of the window(it was still open, just that I was clicking on something else) my gpu usage went from 99% to 15% my PC wattage also went from about 283 to 165 watts.

Evga OC scanner
Furry evga stress test
Fans normal: 205 to 215W max: 220W
Max fans: 210 to 220W watts max: 225W

Prime95 with Evga OC scanner
When doing this test my gpu went from 99% usage to 55% usage I don't really know why though...
Normal fans: 255 to 265W
Max fans: 260 to 265W max: 267W

Ok, so if my computer is using about 300 watts, and I'm adding a max of 150 watts which is the theoretical max a GTX 660 can use, that sets me at a max of about 450 watts. That keeps me at about 70% of my PSU's max of 620 watts. From all f my measurements, my power supply should be able to handle this. Do these numbers seem right to everyone? Is there anyway I might've messed up?
if anything doesn't make sense, tell me so that I can clarify.
Thanks.

djangoringo · Mar 12, 2013

You're fine with two 660 gtx in sli with that psu, and it's not 150W the maximum tdp of the 660 gtx, but 140W, and if you'd seen the 660 gtx(msi hawk) peak power tested in techpowerup it's less than 140W, your psu is a quality one, and it's more than sufficient for it, you shouldn't worry.
It will have good efficiency at load with two cards and with low ripple and noise levels, if it were a generic psu then you should be worried, but you had a seasonic psu which is a high quality one.

pieguyx1000 · Mar 12, 2013

Yeah, I guess that I'm over thinking this quite a bit. I don't know. It's just that when I built this system, I never really though of SLIing, and now that I know I'm going to I want to make sure I can safely(I don't want to kill my first custom PC). Also I know that a GTX 660 isn't going to pull 150 watts. I just said that because that's the maximum it could theoretically because of the 75 watts from both the PCI slot and 6-pin connector. I'm overcompensating. Thanks though.

Also, as a side note, why are SLI minimum watts so high? I read multiple times that the minimum wattage for a PSU doing GTX 660 SLI would be 700 watts.

djangoringo · Mar 12, 2013

No it's not, realhardtechx recommend a 600W psu : http://www.realhardtechx.com/index_archivos/Page362.htm
Your system won't pull more than 450-500W at load, the psu you have is a quality one, even if it overloaded(which it will NOT happen) it has protections that will not damage the other parts that you have, that psu has low ripple and noise levels at load and good efficiency, don't worry, you have a quality psu.

ko888 · Mar 13, 2013

For a system using two GeForce GTX 660 (non-Ti) graphics cards in 2-way SLI mode NVIDIA specifies a minimum of a 600 Watt or greater system power supply that has a maximum combined +12 Volt continuous current rating of 36 Amps or greater and that has at least two 6-pin PCI Express supplementary power connectors. The only card that I know of that deviates from this is the MSI GeForce GTX 660 HAWK 2 GB that requires two 6-pin PCI Express supplementary power connectors for each card.

Total Power Supply Wattage is NOT the crucial factor in power supply selection!!! Total Combined Continuous Power/Current Available on the +12V Rail(s) rated at 45°C - 50°C ambient temperature, is the most important factor.

The Seasonic S12II-620 Bronze (SS-620GB), with its maximum combined +12 Volt continuous current rating of 48 Amps and with one 6-pin and one (6+2)-pin PCI Express supplementary power connectors, is more than sufficient to power your system configuration with two GeForce GTX 660 (non-Ti) graphics cards in 2-way SLI mode.

[Edited to correct wrong graphics card model]

djangoringo · Mar 13, 2013

It's two 660 GTX non ti, he doesn't need molex adapters, each card only requires a 6 pin, so two will require 2x 6 pin, the psu has a 6 pin and a 6+2 pin, like many said the psu will do for two 660 GTX in SLI, even two 660 ti(in that case requiring a molex adapter, but it's fine too), but since the op has already a 660 non ti, he must get another 660 gtx non ti, the brand is irrelevant.

620w max PSU ok for GTX 660 SLI?

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