Someone on here ran a 5970 and a 5770 at the same time although the latter may not have been active while gaming like in my situation.
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GTX 690 in a 2012 Mac Pro
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Someone on here ran a 5970 and a 5770 at the same time although the latter may not have been active while gaming like in my situation.
The reason you're seeing a lot of similar replies is pretty simple -- most experienced people have evaluated the risk and reward, and concluded that a single card that is at or near the 225W limit that the Mac Pro can offer is the best choice. I've been running a single GTX 680 for the past couple of months, and have found it to be an excellent card that is more than enough for the games I play.
What are you going to be using the system for? I'm guessing gaming under Boot Camp, since SLI isn't supported under OS X. What games require a 690 to be playable these days, where a single 680 is not playable? If you're planning for a game that hasn't been released yet, why not get a single GPU now and then another one in 6-12 months when the current products are refreshed? Wouldn't that be a better option? 690s are still going for $999 or more here in the US, from what I can see.
I think splitting the two 6 pins into 8 pin is very risky, it will draw more current then they are designed.
Getting a sigle 680 now and then a single 680 later doesn't help with my problem, I'd have the same power draw dilemma later. 1 690 has less draw than 2 680 and produces less heat. I have found a good deal on a 690 and have my heart set on that card. Crysis 3 for instance needs a GTX 680 for high settings, 690 will see me out a couple of years compare to a 680.
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EI Awesome has already said that each 6 pin provides 75w, two would give 150w through a Y splitter to 8 pin. The other 8 pin source would be from a GPU PSU inside the Mac Pro. Given that the GTX 690 draws 300w max the 150w from each source should be fine on the Mac Pro PCI-E power trace. In theory anyway, unless you actually have something technical to back up 'very risky' i'm inclined to believe the power draw via this method is within limits. Can you provide evidence otherwise?
I'm getting one person saying 225w and one saying 150w (75w via each 6 pin). Which is correct?
I'm not suggesting getting a second GTX 680 in 6-12 months, I'm suggesting you spend that extra $500 on the next-generation card from AMD or NVIDIA once it gets released next year (e.g. the GTX 780 or whatever it will be called). You just stick with the single GTX 680 in the mean time.
If you have a great price on the dual-GPU card and have your heart set on it, then go for it -- nobody is telling you otherwise. It just requires a lot more effort than a single card solution, but you already know that.
Edit: Regarding power, the Mac Pro can provide 225W, 75W from the PCIe slot and 75W from each of the 6-pin power cables. If you find some kind of converter that takes the 2 6-pin cables from the motherboard and combines them into a single 8-pin connector, that should work and give the expected 150W. However, you still have the problem of feeding the card from two separate power sources, which has an unknown amount of risk.
I would imagine that the feed from two different sources can be compensated by linking in a relay to start the second PSU at the same time as the Mac Pro PSU, many GPU PSU units have a plug in molex from the host PSU. If the timings are off ever so slightly I doubt it would be an issue but say it is I imagine the worse to be the card running in a 'crippled mode'. I think that cards are advanced enough nowadays to compensate for delay in power via one of 8 pin inputs, so long as full power is enough after say a second or two I think that would be fine. This is all theory but it looks promising.
The people using the additional 5.25" PSU have not reported their cards stalling on boot, so I would assume the card simply waits until power is detected on both 8-pins before completing its own startup.
You have been told not to split the 6-pin leads and to get an secondary internal PSU instead.
Since you are set on purchasing this card, just do it. Why not write up a How To once you have got it installed and stress tested?
You have been told not to split the 6-pin leads and to get an secondary internal PSU instead.
Since you are set on purchasing this card, just do it. Why not write up a How To once you have got it installed and stress tested?
My thought exactly, the power management must be able to compensate for fluctuation, it's just a question of how much....
Are you aware that I'm not splitting 2x 6 pins to 2x 8 pins? I'm taking power from the 2x 6 pin on the board and converting it to 1x 8 pin. The other 8 pin supply will be from the GPU PSU. Who told me not to split the 2x 6 pin to 1 8 pin?
Let me just say that 580 are particular about their power.
I once used an internal 6 pin combined with an external 8 pin and the card never booted again. I imagine it had something to do with power from one source running the wrong way to the other, ie 11V + running down a 12V - line or some such trouble.
I have a giant box (or two) of dead cards. Each one a sad story. I plan to get to each one and fix it but the truth is most I never will.
If you get an external PSU, use it to power BOTH plugs on whatever card. Trust me on this. The impulse to see "I wonder what will happen if I......" should be avoided here.
I once used an internal 6 pin combined with an external 8 pin and the card never booted again. I imagine it had something to do with power from one source running the wrong way to the other, ie 11V + running down a 12V - line or some such trouble.
I have a giant box (or two) of dead cards. Each one a sad story. I plan to get to each one and fix it but the truth is most I never will.
If you get an external PSU, use it to power BOTH plugs on whatever card. Trust me on this. The impulse to see "I wonder what will happen if I......" should be avoided here.
That's a bit brash, I'm simply wanting more powerful graphics, I don't want kernel panics too!
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The 580? This is a 690 i'm talking about. You mentioned the card died, what happened? Are you just making a best guess as to why it died?
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Is a 450w 5.25 Graphics card only PSU with 2x 8 pin connectors enough to power 1x GTX 690?
As much as I wanted all of this to be internal I'll have to get an external supply if I cant power the card from one 5.25" 450w PSU (Fingers crossed). If i'm forced to use an external I need the thing hidden in a cupboard below my desk, does anyone use an external PSU for this purpose and which one? Cable length is my main concern here - that is the 2 8 pin wires need to be around about 2 metres, any issues with those lengths?
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Of course it is
If the card draws 300W peak and 75W is coming from the PCI-E slot then the GPU psu only needs to supply 225W...
Of course it is
If the card draws 300W peak and 75W is coming from the PCI-E slot then the GPU psu only needs to supply 225W...
Do I need to allow for overheads? Those overheads being the PSU not supplying the full rated 450w performance? Is this still a concern with a modern PSU?
If power draw spikes, say for instance at startup, would it ever try and draw more than 300w? If these are non-issues then i'm set.
This is the supply I have in mind:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817206001
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Back in 2011 a user mentioned his Mac would not boot without the help of a native Mac GPU.
The user was using a 570, would the issue be present in my system with a 690? Would I need to retain a 5770 for instance? I'm fine without boot screens but wouldn't want to have an unbootable system with just a 690.