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Discussion in 'Mac Pro' started by AndreeOnline, Mar 26, 2015.
I have been fighting that same issue as well. Here is the thread on DifferentSLI.
I haven't had much luck getting it to work for me though. I have two identical 980ti, one is MVC flashed.
I haven't post to this thread since I finished the mod, but mine has been going stable for over a year now. It powers my 980ti exclusively (not using the logic board). When I put both in, I use the 6+2 pin connectors from the PSU and the 6 pin from the logic board. Since I couldn't get SLI to work , only one was under full load.
I was able to patch and install the patch, had a popup from windows saying my system is SLI ready or enable or something... but when I go to the drivers page there are no options for SLI so annoying...
Hello, how are we going now with these mods? Are them still valid?
I don't need at the moment but i'm willing to buy one better graphic card soon, from gtx980 to over... and i've read all this topic
Not very sure what you mean, but this mod should be always valid, it's a pure hardware mod. As long as you want to run 1 (or more) high power GPU, you can always consider this mod.
Well... thank you
You don't need to do any special power mods to run a GTX980.
Even though I tincker with computers, I don't feel technical enough to actually do this mod, even with your no-cutting/soldering solution
Are there other "less elegant" solutions to run a pair of amd or of gtx980 ti?
Btw, will this mod even be required with e.g. dual RX480 setups?
Thanks in advance for the help!
The 980ti can run on the internal connectors using a 6 to 8 pin adapter. I don't know about a dual RX480 setup but on paper they should run on internal power as well, each plugging into a 6 pin connector.
The mod feels safer if properly done and makes the mac fans run quieter under heavy load, but I've yet to see anyone reporting power related trouble running any maxwell card on the internal connectors.
A less elegant way to run two high powered GPUS would be to have another PC power supply outside of the macpro and run the 8 pins into the side or the pcie expansion bays (assuming you have one free spot.) This method would practically let you run whatever setup you want without worrying about the mac pro's internal PSU.
You wont need this mod for a pair of RX480s as these cards aren't power hungry. If you get a referenced / non OC version, they're usually only 6 pins and you can have both run on the system power. If both 480s are 8 Pin (usually when OC / custom AIB versions) then you can run off some power from the sata drive bays.
However, running a pair of 980Ti would be trickier, and this mod would make it possible.
I was just watching some videos, and it looks like a solution to internally power two gtx980ti would be to use some power from the pcie slot and some power from 4x sata ports
1st gtx980ti with power from its pcie
+ the two sata of the cd drives slot
2nd gtx980ti with power from its pcie
+ the two sata of two of the hard drive slots
do you think this would this work? (with the right cables ofc)
would fans go crazy? (top much power drawn from the sata ports)
It may work, but may also kill the SATA port. The SATA port only rated up to ~55W, so 2x55=110, may not enough to drive the 150W 8pin input. So far, no one knows how much the cMP SATA port can actually deliver, if the 9820Ti really draw 150W from the 8pin, that mat cause trouble. If it only draws a bit > 100W, then everything will be fine.
I think it can work but it will be unstable, and like h9826790 already mentioned, it has the potential to kill the sata ports. I recently did some power draw testing on two 390X card running in the system using one cMP 6pin on each card and the other 8pin ports are powered externally. During heavy loads, the card did pull its entire designed TDP (~285W) consumption and each 8pin pulled 150 watts which is the max of that connector. I'd be very hesitant to pull that much off the sata ports.
One better way of doing it with two 980ti would be to power the 8 pin connector with a 6 to 8 pin adapter and the 6 pin connector with a dual SATA to 6 pin adapter on both cards. You don't risk frying your SATA ports and we know the PCIe power connectors have an overload protection (and can handle the 8 pin connector from the 980ti), so the worse that can happen if you overload those is your mac shuts down. This would however use 4 SATA ports and I guess the fans would run very loud under full load.
I tried that method with a 390X, using a 6pin PCIe to 8Pin plug. Unfortunately it does start and boot and work on a regular browsing but under load the power cuts off, because the card was trying to pull 150W out of the 75W limit of the 6pin.
Well maybe not with a 390X but it works with a 980ti. I'm not sure how it reacts with two though but it seems the overload protections are independent on both connectors so my guess is that it should work.
I dont have a 980Ti to test out so I can't give my first hand experience on that. However, the non-reference 390x that I have is only about 25W more on power draw compared to the 250W reference 980Ti, so my assumption goes towards them having the same power requirement.
Well this would be unacceptable in my working environment.
How do you set up with 1 or 2 external PSU?
Where can the neccesary cables go into the case?
You'll only need one extra PSU, and you'll need a hard minimum of 300W. I'd recommend 400W+ to keep it safe, and they should be able to fit inside of the DVD tray with the drive removed, and you might even be able to stick it in the cage itself. The PCIe connectors will have to go through the same hole/area that AndreeOnline set it up (on Page 1) and now the only thing you'll need to come up with is the power cord. My for best area to grab it from is to wire an IEC cable and directly solder it to the Mac Pro's 110V inputs at the back end.
If you're willing to just keep the external PSU outside of the MacPro, you can route it through the back and into one of the PCIe expansion slots, given that you still have one open spot.
So what you're telling is that you have to open the PSU and solder inside, which is what the internal mod is about. You would also need to make electrical connections between the two PSUs to synchronise their startup or start your external PSU manually (which means having physical access to it).
The easy and dirty way to use an external PSU it is to leave it outside the mac as it doesn't need any soldering or wiring skills. This leaves you with something looking like this and the external PSU has to be turned on before the mac. You could do a cleaner mod internally but that would end up being way more complex than the mod proposed in this thread.
I don't see how the external PSU mod is simpler (well the dirty way is) or more suitable than the internal mod or pulling from SATA, especially in a working environment. If I were you I'd rather try on internal power first and if that's not enough (or if you need the SATA ports) find a friend comfortable enough with electrical wiring to help with the internal mod.
TDP alone is not relevant, there's the real consumption and also the way the load is balanced between the different connectors. A 780ti shuts down the mac under load whereas a 980ti or Titan X doesn't, and these are all 250W TDP cards. The thing is Maxwell cards don't pull that much current from the 8 pin connector so they don't trigger the 10 amps limit. There are enough people here running 980tis internally so that we know those work on internal power without modding. I can even run my Titan X fully overclocked at 110% TDP running Furmark for hours without the PSU mod. Now that is true for Maxwell cards but won't necessarily apply for other cards and apparently not to the 390x.
Yes but I think itdk92 is trying to do two of them, not one.
Yes, one internal 6 pin can supply the 8 pin connector of a 980ti, there's two of them. The other two 6 pin connectors can be supplied by SATA power. No mod, no external PSU, just four cheap adapters. I think simplicity was the word.
Ah, ok. I misunderstood.
It may work, but really very very close to the shutdown limit, and there are plenty of reports that the 980Ti can shutdown the Mac Pro, just not every single card will do. However, also not every single card (even the none OC card) won't trigger the shut down protection.
Since itdk92 stated that it will be unacceptable for his working environment. I personally won't recommend this config to him.
Well I've checked and there are effectively a few users reporting shutdowns, that's still something to be prepared for but it's worth a try. Now as he doesn't feel comfortable doing the mod himself I'd rather advise him to ask for help doing it rather than using an external PSU. It's a dirty and ugly hack and it's not safe to use on a daily basis unless properly done. This thread has freed us from using this hack so it's hard to recommend it here nor anywhere.