Nate152 wrote:
Hello triangle

That's a power hungry gpu but a 1200 watt psu is enough as long as it has four 8-pin pcie cables.


Click the pic a couple times to make it bigger, this is the specs for the saphire tri-x 390x from newegg.

PSU to be exact is this one:
PSU: "LEPA G1200-MA 1200W ATX12V / EPS12V SLI Ready CrossFire Ready 80 PLUS GOLD Certified Modular Power Supply "
http://www.newegg.com/Product/Product.aspx?Item=N82E16817494011
In the specifications read:
PCI-Express Connector: 8 x 6+2-Pin.
CrossFire: CrossFire Ready.
SLI: SLI Ready.
Is this correct Nate?

triangle wrote:
I am curious about running two 980 Ti's in SLI and one 285gtx as primary Physx all at once. Is 1100 watts the wattage needed for all three to run on mobo?

A reference GTX980Ti requires a 250W PSU (and recommends a 600W+ PSU) with 6-pin and 8-pin connectors.
A reference GTX285 requires a 204W PSU (and recommends a 550W+ PSU) with two 6-pin connectors.

You'll need a PSU with enough 6-pin/8-pin connectors for your three cards, of course. And the extra 12V PEG output (Asus "EZ-Plug" or whatever) to feed more PCIe power into your motherboard, if supported. Ideally, you'd want all three cards on the same 12V rail, or at least balanced evenly across two or three 12V rails.

I think a 1000W Bronze PSU might be enough, but 1200W Gold would be much better (and last much longer) running peak loads - an over-rated PSU will also tend to run quieter and cooler under normal loads than a proper-rated PSU. You'll certainly need a mighty PSU if your system is packed with lots of power-sucking drives and accessories.

From what I've seen online, people running strong 3-SLI GTX980Ti setups seem to usually have 1500W-1600W+ PSUs, while a few with 900W, 1000W, 1050W, and 1080W PSUs report issues at peak load. Price difference between a decent 1100W and a quality 1200W-1250W PSU is quite small compared to the price of twin GTX980Ti cards, I'd say it's not worth worrying about determining the exact threshold while it is worth spending a little extra to deliberately oversize and simply remove PSU troubles from consideration.