PSU and efficiency- in idle and under load

[branskyj]

Hi all,

I am completely ignorant when it comes to that kind of stuff so bare with me please.

Would a 1500W PSU use the same amount of power (in idle and under load) as a 850W PSU given that the PC stays the same?

In other words- does a PSU only use the amount of power all PC components require or the PSU itself taxes as well.

I am thinking of buying a 1500W PSU and my biggest concern is the electricity bill.

 

Thanks guys.

[Dimitris Tolios]

Your biggest concern should be "do i need a 1500W" to begin with.

The price difference for a good 1500W PSU in comparison to 1000W and 850W units is not insignificant, and paying up-front for something you potentially won't need, is not a wise choice.

 

If you are investing in a new, powerful system and you are concairned with power efficiency, you should aim for a gold or platinum certified unit - preferably from a respectable PSU manufacturer. Enermax and Seasonic are a couple of the best brands in my mind, but Seasonic does produce many of the best PSUs out there for other companies too.

 

Most modern PSUs operate at maximum efficiency at around 50-60%, but due to "economy of scale" reasons, really good 850+ W units provide pretty level efficiency graphs from 20-30% loads already. In the long run, most modern single CPU / single GPU systems, even with power hungry components (sandy Quad/or even 3930k + a GTX 580 for example) is around 430-450W under heavy load, putting it right at the sweet spot for a 850W PSU.

 

With 2x SLI 580s, you would be around 660W or lower. Again, manageable with a really good 850 (like Gold/Platinum quality units), and newer GPUs like the AMD 79xx and nVidia kepler GTX 680s will save you about 50W off both idle and load measurements per card.

 

A Seasonic 860W Platinum is according to anandtech measurements 93.03% efficient @ 50% load and 91.99% effic. under 80% load. That fits our above scenarios within 1%, which is technically identical, but we are talking about one of the newest and "Shiniest" 850s out there, rated Platinum.

 

1500W sounds overkill unless it will be powering a couple of xeons and 3-4 GPUs at the same time, and those rarely rate above 80+ silver.

 

I would say that if you want some room to play with 2x CPUs and/or 2x GPUs, a 1000W PSU is ok, a 1200 more than adequate. I don't believe there are platinum 1500s, you can find some pretty good Gold rated 1350s and 1200s tho around the $300 mark, and platinum 1000s around the $250. I would go with one of those, with preference on the platinum series if you are not planing on pushing anything with more than the single CPU/2x Fermi based hi-end GPU mentioned above.

 

@ idle i just expect platinum > gold > silver > bronze regardless of the max rating.

[branskyj]

Thank you for the detailed answer, Dimitrios.

I guess I should have explained more- I am running a 3930k CPU and my goal would be to add two or three GTX 590s (or GTX685 this autumn) for the sole purpose of GPU rendering (Octane), not gaming. Probably as you said I won't need a 1500W at first but my intention was to add another GTX down the road.

Thanks for the answer and I will check what reviews has Anandtech on Platinum and Gold PSUs.

All the best mate.

Julian.

[Dimitris Tolios]

Woot, beasty rig

Well, those 2-3x 590s will suck a lot of juice. I don't know how octane manages VRam memory usage, but if it's manageable with the 1.5GB/GPU 590s allocate, that should be pretty fast. Haven't looked up exact figures, but I would expect 2x 590s be a tad less demanding than 4x 580s...still crazy tho. You will be stressing a 1000W PSU under heavy loads, so a 1200W would not actually be a waste.

 

If power efficiency is your goal, I would skip the 590s tho...the new generation (kepler) vastly improves energy efficiency - both under load and when idling. And saving 5% overall efficiency with the "perfect" PSU when your values are nearly double with an idling fermi vs. an idling kepler, kinda beats the purpose of the really good PSU in the "conservation" point of view.

 

It's like stretching the "fuel efficiency" for xtreme supercars - power needs juice. Lots of power, a lot of juice. Period.

 

On the lucky side, the same PSUs will be a tad better over in UK...110v does not help their battle, 220v is easier on them.

 

Also, depending on your case (and you will probably need a big case) you might try a dual PSU configuration - used to be the only way a few years back.

[branskyj]

Hm, I didn't even know about the "dual PSU configuration" option. That actually sounds very interesting considering the insane prices for high-end powerful PSUs. That way I can get (hopefully) two PSUs. I will look into it now.

Thanks for the idea, Dimitrios.

Cheers,Julian.

[Dimitris Tolios]

Hm, I didn't even know about the "dual PSU configuration" option. That actually sounds very interesting considering the insane prices for high-end powerful PSUs. That way I can get (hopefully) two PSUs. I will look into it now.

Thanks for the idea, Dimitrios.

Cheers,Julian.

 

Well, just be careful cause you will be in need of quality PSUs either way.

I did some quick reading around (mainly http://www.overclock.net and overclockers forums etc) and people have mix feelings about dual PSUs...for a reason. Some risk is involved. But I don't believe there are other ways to achieve such high end, multi GPU/CPU configurations.

 

Some ppl report wall-measured draw of around 770W for an overclocked 3930K, and 2x o/ced 580GTX. Your 2x 590s - if also overclocked will flirt the 1000+W, so you are looking into 1200-1350W PSUs already. I don't have sources to quantify what happens past that point. Most people writing in forums for such things are gamers, and thus see things only within the SLI/Crossfire scope - it such cases, more than 2x 590s or 4x 580s make no sense as that reaches the "quad SLI" limitations.

 

Octane and other unbiased engines that utilize compatible devices regardless of SLI/CF are not in their interests, so 3x 590s are useless for them.

 

Newer drivers report that the performance deference between kepler (680 GTX) and fermi (580/590) is dropping, with fermi being always faster but 680s not being completely embarrassed. At least for VRay RT GPU which I try to follow in chaosgroup's forum.

Taking into consideration how easier it is to power 4x Kepler cards vs. the 2x 590s, plus the versatility of the extra Vram the former will have (even @ 2GBs, and 4GBs versions are coming), the 590s are not that desirable.

 

At least not past the 4x GPU cores at least, as that will start introducing power and heat issues, with diminishing performance gains.

 

If you were doing something reeeeeeally GPU intensive in computation tasks, that the performance difference would actually improve your income conciderably, you might consider taking a completely different path than the Sandy E i7 platform: I've been "accused" of wet teenage dreams, so take a look at the TYAN FT72B7015 barebone...it's a dual Xeon platform, designed to run up to 7-8 dual width GPUs, with 8x 16x wide PCIe ports. A bit pricey, but includes 3x 1200W reduntant PSUs (the effective max load is 2400W, the 3rd PSU acts as a backup should one of the other 2 fails).

 

With a couple of 5620s, 8x 580s 3GB and 24gb ECC it will set you back some $9000.

Ventor assebled such systems are selling for a bit more (take a look at http://www.renderstream.com/ for example). You can also "spy" on their configurations, and maybe value engineer some of your aspirations for multiple GPUs