Is 750W enough?

[andrewhutt]

I am looking to get either a Corsair 750W RM or CS750M but my main question is whether it will be enough to run two GTX770's (GIGABYTE 3X) in SLI. I will initially buy one 770, and upgrade to a second as necessary.

Other Components:
Gigabyte Z87X-D3H
Intel i5 4670k OC 4.2GHz
2 x Corsair LP Vengence (2x4gb)
Arctic Cooler Freezer 7 Pro V2

[MrJim]

I came across this website which might help:

http://www.realhardtechx.com/index_archivos/Page362.htm

It seems to suggest that 850W is recommended for 770's in SLI...

[GeorgeStorm]

I would personally think it would be fine.

The best thing to do is ask people who own them to test, or find reviews which show power consumption, since the 'recommended' power for graphics cards is normally waay higher than it needs to be.
I use a GTX670 and I haven't seem my power consumption go over 300W (peaked at around 270W whilst playing Metro: Last Light) and yet I think they recommend a 500W PSU as a minimum.

[kalniel]

Legit Reviews tested reference 770s in SLI with an X79 platform and the measure at the wall came to ~550W average gaming load. I would guess that an overclocked i5 might match the normally more power hungry X79 platform, so that would suggest needing around a 500W rated supply for sustained loads (with the quality to cope with burst loads a bit higher). A good quality 750W (such as the RM series appear to be) should be plenty of scope and put you into an very efficient region of the PSU.

But check other reviews too. Xbit labs test came to 700W at the wall (with other system components that needed more power than yours). Guru3d estimate that the card load for 2x770s was about 400W.

[Bambooz]

A single GTX770 is rated 230W max., so 460 theoretical watts in SLI.
I doubt the "rest" of the system would consume more than 200W, even with CPU OC.

Kinda reminds me of my old Core 2 Quad Q6600 (95W) system with the puny little HD6870 (151W). All PSU calculators and most people on forums said I'd need at the very least a 600W PSU, which was obviously nonsense. I went for a good 430W PSU and still had lots of headroom.
(in fact, that PSU powered my i5 2500k @ 4.8 at first, till I replaced it with a new one with cable management)

[Willzzz]

750W would be OK, but since you haven't bought anything yet I would go for 850W.

A PSU always prefers to be around 50% for optimal performance.

Are you 100% certain that you will SLI?

[andrewhutt]

Thanks everyone for your input. I suppose I would be grateful if anyone has two 770's what their power usage is at running idle / max.

Willzzz - well it really depends on how much the games and graphics develop in the next few years whether I buy a second. I would like the option of adding a second though.

[TheDutyPaid]

Willzzz - well it really depends on how much the games and graphics develop in the next few years whether I buy a second. I would like the option of adding a second though.

The way things are going, in a few years you probably be replacing the 770 with a unit that plugs in by USB, costs about £10 and is 20 times more powerful.

[watercooled]

PSUs don't 'prefer' any load TBH - efficiency may peak somewhere in the middle but a quality power supply will hold good efficiency up to 100%.

About the only performance metrics to consider with PSUs are ripple, transient response and possibly voltage regulation. In reality, computer components don't care about spot-on voltages so provided they're in-spec that's more than enough. Ripple and transient response are things decent power supplies are designed to perform well at.

PSU calculators and GPU manufacturers tend to massively overestimate PSU output in order to account for rubbish PSUs among other things.

Those Xbit results look high even compared to other overclocked 2011 systems. Legit reviews has gaming load <550W AC, Anandtech <500W. Factor in unrealistic load in something like furmark, according to techpowerup maybe 40W per card, and another 100W for the CPU just in case (again unrealistic), you're still below 750W total.

http://anandtech.com/show/7492/the-g...0-ti-review/15
http://www.legitreviews.com/nvidia-g...rround_2210/11
http://www.techpowerup.com/reviews/N...TX_770/25.html

[Shirty]

The short answer is yes, you will be fine with a branded 750W model.

[andrewhutt]

PSUs don't 'prefer' any load TBH - efficiency may peak somewhere in the middle but a quality power supply will hold good efficiency up to 100%.

About the only performance metrics to consider with PSUs are ripple, transient response and possibly voltage regulation. In reality, computer components don't care about spot-on voltages so provided they're in-spec that's more than enough. Ripple and transient response are things decent power supplies are designed to perform well at.

PSU calculators and GPU manufacturers tend to massively overestimate PSU output in order to account for rubbish PSUs among other things.

Those Xbit results look high even compared to other overclocked 2011 systems. Legit reviews has gaming load <550W AC, Anandtech <500W. Factor in unrealistic load in something like furmark, according to techpowerup maybe 40W per card, and another 100W for the CPU just in case (again unrealistic), you're still below 750W total.

watercooled - thanks for the advice and I have briefly used these websites, however I would have liked some input from someone who has this kind of set-up. I presume that since I will be purchasing a Corsair that ripple, transient response etc. will not be a problem (as it is a recognised and established manufacturer)?

I am going to buy the Corsair 750W RM based on all the information above. Million dollar question is, is it Seasonic that is the supplier of the Corsair 750W RM (just branded Corsair), or another supplier?

[watercooled]

Corsair are generally fine, however they're currently producing some questionable quality units IMO.

The RM 750 is made by Chicony (not a bad thing) but TBH isn't one of the best PSUs you can get.
http://www.hardocp.com/article/2013/..._supply_review

I think there's a new version out but I can't seem to find any reviews of it, and I'm not sure how you'd know which version you'd get since they share a model number.

Edit: TBH I don't know what's happened to most of Corsair's decent PSU lineup in this output range, EOL'd perhaps? At the low end they have the GS and RM series, neither of which I'd use in my own system, and then they have the AX series which are good but expensive.

Being a Corsair sub-forum I don't want to appear trollish, but based on what I can find in stock at various UK retailers I could only really recommend the AX/AXi series, but they cost ~50% more...

Edit2: Here's a review of what is probably the new revision of the RM series: http://www.jonnyguru.com/modules.php...Story&reid=369

Much better overall, but the capacitor choice leaves a lot to be desired TBH.

[andrewhutt]

That is disheartening. I felt I had spent a great deal of time looking at PSU's and thought I had the right one. Back to the drawing board it would seem.

Apart from a Corsair, would you recommend any other brands? I basically want a 750w (hybrid/fully modular) and preferably 80+ gold at around the £80mark. This may seem like a bit of stretch now to satisfy all of the above.

[watercooled]

This is a Corsair sub-forum so the open forum would be a better place to ask for general advice.

However, having looked at that review I posted in edit2, it seems the updated RM series are much improved over the original ones. The problem being it seems checking the serial number is about the only way to tell what version you have.

I could more easily recommend some of Corsair's older PSUs but as I said it seems they've been end-of-lined without direct replacements unfortunately. Either that or retailers just aren't really interested in stocking them.

The CS series also doesn't look bad, but has the same problem with iffy capacitor selection. This however may not be as big of a problem as it was a few years back with the 'capacitor plague', I'd just expect better for the money and considering what Corsair offered in the past. The RM series uses a premium brand input cap but cheaps out on the secondaries; I think I'd much rather have it the other way around TBH since input cap quality tends to be less critical to performance.

Have a look at this link if you want to find decent reviews of PSUs: http://www.realhardtechx.com/index_archivos/Page447.htm

[jonnyGURU]

Let's summarize this with some cold hard facts.

The unit at [H] shut down due to some pretty unusual circumstances. He ran it in an incubator with no airflow (the incubator uses heating elements to warm up.) and the testing temperature was 45°C while the RM is only rated at 40°C.

The unit that Jeremy reviewed, which is the same Chicony platform as the one [H] reviewed, is actually NOT a "new" version of the RM. If you look at the serial number you'll see that it starts with 1336. The "new" versions have serial numbers that start with 1341.

Why didn't it shut down? Jeremy points it out here: "First, I don't test things at higher temperatures than they're rated for. Second, my hot box insures airflow through units when they run fanless."

There wasn't a QC issue with the RM. They are tested in burn-in cabinets at 40°C, but those have airflow. Those PSU's are not made to operate in a vacuum under heating elements. The likelihood that anyone would run into the issue exhibited at [H] is very rare. Let's just say, you'd have to be running your PC, locked in a closet, in a house without AC, located somewhere in the Sahara desert. That said, "improvements" (or, as I would prefer to call it "fail-safes") have been installed in newer versions to ensure they work under virtually any extreme condition. Originally, the same thermistor was used to control the fan and OTP (over temperature protection), but OTP would trip before the fan turned on during [H]'s testing. So a second thermistor was added just for fan control.

As far as the capacitor choice goes: Corsair is very careful with the components they choose to ensure there are no premature failures. Because newer PSU technologies result in less ripple current and better efficiency results in less heat, capacitors are subject to a lot less stress than in older PSU designs. I actually wrote a Q&A type of blog on the whole cap selection process and attempt to dispel some myths. I'm not aloud to post URLs because I don't post enough here, but if you just Google "Corsair Capacitor Blog" you'll find the post. Or, corsair dot com slash blog slash capacitor.

[andrewhutt]

Excellent, thanks for all your help watercooled, it is much appreciated. I will have a look at reviews and see if there are any in my price range!