View Full Version : Quad GPU and power rails?

27th August 2009, 00:36
I am trying to plan for the future. And make sure that I buy a sufficiently beefy CPU.

How important are the AMPS on the 12V rails?

Most 1000W units have a combined 70-85A single +12V rail, or several 20A +12V rails.

Now, the GTX295 states it needs 550W on 44-46A +12V rails.

Still I see lots of tests out there where they "okay" 20A +12V rails modular PSUs for multi GPU setups.

A 1500W PSU with 40A on each +12V rails is the most juicy I've found, other than that I've seen some 1010-1248W PSUs where the rails rate from 30 to sub 40A on the +12V rails.

What gives?

At the same time I read users with 1000W PSUs complaining that their spanking new GTX295 cards hang after 1 minute, while still being cool. Is it not enough juice, are they feeding with 20A +12V rails?

The two PSUs I'm considering is either a CORSAIR 1000W with 40A +12V rails, Termal Take Tough Power 1500W 40A +12V, or the M12D 850W 20A +12V.

But I'm confused as what amps the +12V rails need to provide to four GPUs as it would be in a dual GTX295 setup.

27th August 2009, 00:54
It seems that it's Nvidia GTX295 that are insanely amps hungry.

The ATI Radeon HD 4870X2 will be happy with 20A on the +12V rails as it has certified the Dark Power PRO 1000W by "be quiet!" to work with two 4870X2 cards.

27th August 2009, 01:36
An 850W PSU is good enough for 2x GTX295's in quad SLI. However it is always better to get a more powerful PSU than your system needs so it isn't being stressed and is running below its limit. So a 1KW PSU would be the best to go.

A Thermaltake Toughpower, Enermax Galaxy, OCZ ProStream or any other similar 1kW good make PSU would be fine.

My main PC is currently using a Thermaltake Toughpower modular 750W PSU and I'm very happy with it. Quiet and very stable. Plus the modular cables mean you only have to have those in the system that are being used.

Regarding GTX295's, I just don't see the cost of 2 of these cards being worth it at all. Yes they are great cards, but I've also heard the quad SLI is also not as good as nVidia are making out and isn't delivering the promised performance increases.

I would personally stick with 2 ATI 4890's in crossfire. The combined cost of these is less than one GTX295 and they deliver great performance for the price.

27th August 2009, 02:06
So I shouldn't worry about the amps being just 20A on the +12V rails, vs some PSUs that are 40A on the +12V rails?

27th August 2009, 02:38
I just read somewhere that PC P&C's Siencer 910W PSU is certified for quad SLI of GTX 295.

Looking at the spec of the PC P&C 910W PSU it has a single 12V rail rated at 74A with Max Power of 888W, so that explains why it is good for quad SLI 295's as it easily has the power on the 12V to deliver enough for two cards.

Therefore a PSU over 900W is the minimum to look at, and one that has less 12V rails offering more Amps per rail, rather than most these days that have 4 or 5 12V railes spreading their power output between them and only delivering 18Amps on each rail.

Kin Hell
27th August 2009, 09:44
@ Arnljot

Make sure the PSU you buy has a Single 12v Rail. They are by far the best PSU solution for modern day Pee Cee's.
Get yourself the Red 750W PC P&C PSU (http://www.overclockers.co.uk/showproduct.php?prodid=CA-004-PP&groupid=701&catid=123&subcat=1104) & that will be more than enough for a single GTX295 with 60A on tap. If you want to go Quad SLI at a later date, you'd need to be in the 1KW & upwards bracket. The 900W PC P&C is just a bit shy for Quad SLI with only 74A available. 90A is about right, but get ur wallet out for their 1.2KW affair.
Tagan use to be good, but they got very pricey compared to PC P&C. These bad boys are the Rolls Royce of PSU's & no matter what you hang off them, they just don't budge.