dual 7990s with Cooler Master GX 750W PSU

[skidkid87]

I was thinking of running dual ati HD 7990s and looks like they both need 4 8pin PCIe power connectors in total, my PSU have them 4x 6+2PCIe power connectors.

So I was asking since mostly it shows that to run both 7990s in crossfire I'd have to have a PSU that's atleast 850W, but my PSU has the needed connectors.

so I'm basically double checking if I can have both cards without having to upgrade my PSU, as basically there's nothing over 750W that you can buy over the shelf, you'd have to custom order it or you'd have to buy it online, so I'm checking before I have to go through a lot of hassle on this

for my build I currently have:
CPU: core i7-3770 (no overclocking)
MB : Z77X-D3H
RAM: 4 DDR3 1600 MHz Kingston Xtreme blu
HDD: 2x WD velociraptor 10,000 RPM 600GB (RAID 0) on sata 6Gb/s
1x Green caviar 7,200 RPM 250 GB (non RAID) on sata 3Gb/s
fans (all are 120mm) : 6x Coolermaster LED fans
1x coolermaster standard fan (came with the case)
Optical: 1x DVD/CD burner on sata 1.5 Gb/s
PSU: Cooler Master GX 750W 80%+ Bronze

and I only have 2 USB (keyboard and Mouse) ports used at all times, I usually connect one more USB 3.0 external HDD and maybe one more USB 2.0 external HDD

that's all the information I have to help you calculate the power consumption

 

[animal]

a single 7990 requires at least a 700 watt psu. X-firing a pair would require something in the neighborhood of 1200 watts.

 

[Lumber-jack]

7990 has a TDP of 375 and they recommend about 850 watts for one. You would need 750 watts just for the 2 video cards alone. If you aren't running many things in your computer you might be able to get away with a little less than 1200 but I would error on the high side than low. My modular power supply I am sure has enough connections to hook both up but its only 860 watts. You PSU would just do one never mind it doing two. Why are you giving us all the information when you can just do it yourself online in less time?

 

[skidkid87]

the reason I was asking is that I already have 4x 8pin PCIe power connectors and I was wondering if I could pull it off since they only need 4 8 pin connecters combined

anyways I just got my 7990 and it generates an intense amount of heat so running 2 of them most probably will need water cooling as air colling will not be enough, 1 card alone runs at 80 degrees Celsius under load and I find my PC generating alot of hot air when I'm gaming so 2 of them for me is out of the question now, as I didn't know that and my Case does not have enough room for water cooling

but at least it runs on my 750W just fine, no problems here, thanks for your time

 

[Lumber-jack]

You got me thinking and I did a little research and it would be wise to use water blocks on two 7990's and there is some people who have done that with success. It is expensive though at $150-200 per block plus the other parts by the looks of it. Then you need a new 1200 watt PSU so I was thinking instead of pulling my Cosair 860Axi I could use a second PSU with a relay kit that is worth $20.

On that note my 7990 was pushing 100C when I was running some fractal tests so I wouldn't worry about 80C. If I see the 7990's drop again I think I will try it just for the hell of it.

Curious if you have coil whine with yours? I am okay.

 

[17seconds]

Mandatory reading:
http://www.tomshardware.com/reviews/radeon-hd-7990-crossfire-overheat,3539.html

 

[skidkid87]

You got me thinking and I did a little research and it would be wise to use water blocks on two 7990's and there is some people who have done that with success. It is expensive though at $150-200 per block plus the other parts by the looks of it. Then you need a new 1200 watt PSU so I was thinking instead of pulling my Cosair 860Axi I could use a second PSU with a relay kit that is worth $20.

On that note my 7990 was pushing 100C when I was running some fractal tests so I wouldn't worry about 80C. If I see the 7990's drop again I think I will try it just for the hell of it.

Curious if you have coil whine with yours? I am okay.

no coil whine here, can't hear it if it's there, the card is inside a closed cooler master elite 371 case with 7 120 mm fans cooling the case (4 intake and 3 exhaust) but all of that and the case is pritty much silent, no problems here, but I always have my AC on to cool the room to 23 C when I'm gaming that's probably y it runs at 80 C