Little help with GTX280 SLI on an Enermax Infiniti 720W

I'm building a new Core i7 system and planning to run two GTX 280s. Everything I've read suggests that 720W is hugely adequate for such a system, but I'm a little worried because of Enermax's literature.

Two GTX 280s will require two 8 pin PCI-E plugs and two 6 pin PCI-E plugs. While the EIN720AWT has three 12v rails, it has only one 8 pin and two 6 pin cables. Now, in it's bag of modular cables, it came with one which takes two 12v peripheral plugs and turns them into an 8 pin PCI-E cable, straight out the back of the PSU, without dimestore cable adapter trickery. That would solve the problem, but for the fact that the manual specifically forbids the use of modular PCI-E cables in "peripheral" plugs, as well as using peripheral cables in PCI-E plugs.

So it's forbidding me to use the modular cable adapter that came with the PSU!

It may be completely wrong, but what I've worked out is (Giving Jonnyguru more weight than the manual):

12v rail 1: PCI-E 6 pin (three 12v peripheral plugs available)
12v rail 2: PCI-E 6 pin, CPU 4+4 (three 12v peripheral plugs available)
12v rail 3: PCI-E 8 pin, 12v lines in ATX connector (zero 12v peripheral plugs available)

So assuming I use the 8 pin and 6 pin from 12v rail 3 for one card, and the 6 pin from 12v rail 1 for the other card, where should I plug in the second 8 pin adapter? The wattage will easily support two heavy usage cards and a beefy CPU, but should I heed the manual's warning anyway? Is it unwise to span multiple 12v rails for one video card?

Here's the Jonnyguru article on this particular PSU, but I can see already that the literature he had is outdated, mine gives more information than his does.
http://www.jonnyguru.com/modules.php...p=Story&reid=2

And the PSU's manual
http://www.enermaxusa.com/support/do...l_infiniti.pdf

At the top of page 9 is the diagram of the plugs on the back of the PSU. One 8 pin cable is fixed and not shown. The two "PCI-E ONLY" plugs are used for 6 pin cables. If you look on page 10, you can see the adapter I'm hesitant to use, EMC009. It's even got black ends on the PSU side of the cable, like it's meant to be used in the peripheral plugs the manual strictly forbids use of.

Generally you shouldn't power a single video card off of multiple rails. I'd probably recommend just running one card off the second rail and one off the third, providing you don't have too many HDs and other things running off of molex connectors. If you do have a lot of HDs, you'd probably be okay with using the 6-pin from the first rail and taking an 8-pin from the second.

Right, I forgot to list my devices. I don't have a lot running, one DVD drive, two HDDs and three 120mm low-RPM fans.

In that case, I suggest you power one card off the second rail and one card off the third.

Sorry for dragging out what should have been a simple problem, but I have new info, and my first post was wrong. It's been edited accordingly.

According to this image and this chart, the rails are divided thusly:

12v rail 1: PCI-E 6 pin (three 12v peripheral plugs available)
12v rail 2: PCI-E 6 pin, CPU 4+4 (three 12v peripheral plugs available)
12v rail 3: PCI-E 8 pin, 12v lines in ATX connector (zero 12v peripheral plugs available)

Knowing this now, one of the cards MUST bridge two 12v rails, specifically the one using rail 3's PCI-E 8 pin. Even with only one card, using the non-removable 8 pin PCI-E cable as suggested requires spanning two 12v rails.

I suppose I'm just looking for confirmation now, the only solution seems to be to use the 8 pin from rail 3 with the 6 pin from rail 2 for one card, and the 6 pin from rail 1 with the 8 pin adapter cable also in rail 1 for the second card.

Yes, in that case it seems you don't really have a choice.

I got a confirmation from Enermax on my last post there. That's the best layout to avoid overtaxing any of the rails, with one card on rail 1 and the other card on rails 2 & 3. I thought they'd make excuses or tell me I shouldn't power this much from their PSU, I was pleasantly surprised!

Well, actual power capacity isn't really an issue. The PSU has plenty of power for your components.

Originally Posted by Zero82z

Well, actual power capacity isn't really an issue. The PSU has plenty of power for your components.

Do you ever sleep? lol Seems like you've replied within 30 minutes of all my posts!

True, but they didn't try to be sneaky snakes and tell me I had to procure a beefier PSU, nor did they cover their tails and say "don't do that" to avoid liability. I'm impressed by their demeanor more than their actual products (which are already very impressive), and that's what'll keep me coming back for more Enermax solutions in the future.

Thanks for all the replies! Case closed!

Originally Posted by Flubb

Do you ever sleep? lol Seems like you've replied within 30 minutes of all my posts!

It's 6:30PM right now where I am. Not exactly bedtime for me . You just happened to make your posts at times that were fairly close to when I was around.

I personally would be a little weary of loading a 720 watt PSU with 2 large video cards. Yes it does have a decent amperage but you are probably running that PSU at close to 100% capacity thus reducing its life span.