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Trying 3-way SLI gtx970's on 750w?

post #1 of 9
Thread Starter 
Now this might sound like a bad idea, but hear me out. My two brothers and I each have a 970 making three total, so sure enough having my x99 system means I can actually do 3-way SLI for some fun benching and whatnot.

Now my 750w PSU definitely sounds like it isn't enough, but today I bought a watt-meter and plugged it into my PC with 2-way SLI. The max under full load I've seen was just 420W and that's the wall, a bit above what the PSU is providing. So surely there is enough headroom for another card and a bit more CPU OC'ing right?

So would 750W be reasonable for just some short term fun? This of course isn't some 24/7 plan. I use a Corsair HX750 Watt psu which only has four pci-e connectors, so I'd have to do two dual molex to pci-e converters to get all the power connectors I need.
post #2 of 9
750w is okay if that's what you got on hand. Remember, that 420W that you're seeing pulled from the wall is really only like 380W assuming 90% efficiency that the PSU needs to output to the computer. You're using only half of the power the PSU is rated for. You're fine.
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post #3 of 9
What kind of load did you put on the GPU's? Any CPU load? As Syan said, 420w from the wall is actually around 360 used internally (DC). You should be perfectly fine as long as you stressed the GPU's with Kombuster or Furmark etc.
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post #4 of 9
Sounds like plenty to me. These vid cards these days are not sucking the power grid like years ago. I wouldnt hesitate to run 3 970's on a solid 750w PSU.
post #5 of 9
Thread Starter 
Loaded psu with cinebench and furmark running and peaked right at 500W, so still plenty of headroom for another card. thumb.gif
post #6 of 9
At stock to very mild overclocking you will be fine. However once you start overclocking the CPU and GPUs you will have a problem. I run a X79 setup with 4way 970s and I can tell you once you start cranking the clocks you start needing a lot of power. I was running 3way on a 875w tough power and it did fine until I was running over 1450core and cpu@4.8ghz. Had to move to a PC power and cooling turbo cool 1200 to be rock stable. Now I'm running a ZX1250 and ZX1000 together and haven't looked back. I would use what you have then go to a good solid 1000W.
post #7 of 9
Thread Starter 
Quote:
Originally Posted by Moparman View Post

At stock to very mild overclocking you will be fine. However once you start overclocking the CPU and GPUs you will have a problem. I run a X79 setup with 4way 970s and I can tell you once you start cranking the clocks you start needing a lot of power. I was running 3way on a 875w tough power and it did fine until I was running over 1450core and cpu@4.8ghz. Had to move to a PC power and cooling turbo cool 1200 to be rock stable. Now I'm running a ZX1250 and ZX1000 together and haven't looked back. I would use what you have then go to a good solid 1000W.

If I up my CPU clocks any more it would just be from 4.2 to 4.5-4.6 or so. The two cards I have now don't like to OC very well with each other so with three it'll probably be pretty minimal OC. At most I would be running 3-way for a few hours so no need to change cpu.
post #8 of 9
I went through 15 cards to find for matching cards that would all do 1600 on the core with custom bios. I run 4way at 1500. 3way at 1525 with no heat issues as I can use slots 1-4-7 so perfect spacing for air cooling.
post #9 of 9
Thread Starter 
What drivers are you using? It seems to be the most limiting factor actually for me. I know broth cards can do ~1570 core at least each, but even at 1500 it can be unstable. I currently have 353.62 as it seems to be working better than some of the newer drivers I've tried.
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