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Powering a GTX 980ti in a CMP

D

deppest

macrumors member
Original poster
Oct 6, 2009
69
8
Hi chaps

I am thinking about putting an EVGA GTX 980ti (250W) into my cMP, mostly for CUDA compute/rendering. I am aware that the card could be connected directly to the two 6pin mini connectors in the CMP, i.e. by using 8pin->6pin mini and 6pin-> 6pin mini cables and some people seem to be quite happy with that setup. However, being aware of the 2x75W limit those two 6pin mini connectors in the cMP can safely provide (according to specs) I would prefer to distribute the power draw of the card more evenly by connecting both the 8pin PCIe and the 6pin PCIe on the card to both mini 6pin in the cMP, kind of crosswise. Difficult to describe, please take a look at the picture. Would really appreciate your views on this.
 

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yes, I know about it and like it a lot but I do not currently want to invest into this kind of work
 
2x mini 6pin -> single 8pin -> 2x 6+2pin

I think this is a simpler way to share the loading between the two mini 6pin. You only need a single 8 pin as the bridge, but not 4x 6pin.
 
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Fwiw my Titan X(M) SC is running on just a mini six to 8 pin and mini six to six pin without issue. I understand the 980ti can be slightly more power hungry but I suspect you'll be fine however you wrangle it.
 
It seems okay in theory but there are already known working solutions, so I'd stick with what people have tried and proven to work.

But if you really want to balance the load, I'd use H9826790's method. Your diagram has a lot of y-cables and adapters, leading to a rat's nest of cabling and extra expense.
 
I've been using a 980ti in a 5,1 for a week now with no issue.
I've got to admit I didn't know about the 75watt x2 limitation.
I got the card from Mac Video Cards (who I'm impressed with) and just sent them an email for clarification on this. If anyone knows it's them.
 
I have been using the 980Ti in my Mac Pro for quite some time now. I power it with one mini-6-pin to 8-pin, and one mini-6 to 6-pin. Works fantastic, even when under full load/benchmarks.
 
Here's what Chris at Mac Video Cards said about installing a 980Ti into the motherboard:

"Yes, in general it’s fine. If you machine is fully loaded (full hard drive bays, multiple PCIe devices, CPU upgrades), then it’s recommended to use an external power supply."

This raises the question "what is fully loaded"?
And the related question "what happens when I go over?" Does the machine just not start up or do I fry something?
 
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Mine is fully loaded. 6 drives, 4 pci cards, 96GB Ram. My 980ti was drawing too much for my power supply to handle, my machine would just randomly reboot. I got a 500w PSU just for the 980ti and now it's running like a champ.

Chris at Mac Video Cards also told me this was normal.
 
JesterJJZ said:
Mine is fully loaded. 6 drives, 4 pci cards, 96GB Ram. My 980ti was drawing too much for my power supply to handle, my machine would just randomly reboot. I got a 500w PSU just for the 980ti and now it's running like a champ.

Chris at Mac Video Cards also told me this was normal.
Click to expand...

I guess with a Single CPU Mac Pro your configuration would not be a problem.
 
JesterJJZ said:
Mine is fully loaded. 6 drives, 4 pci cards, 96GB Ram. My 980ti was drawing too much for my power supply to handle, my machine would just randomly reboot. I got a 500w PSU just for the 980ti and now it's running like a champ.

Chris at Mac Video Cards also told me this was normal.
Click to expand...


Thanks. Good data.
I just upgraded everything and haven't had a crash. I'll get a PSU if that becomes a thing. Glad to know it's just an inconvenience thing more than something scary
 
Single 6-core (upgraded) W3690, 3x16GB RAM, all drives and PCI slots filled, Maxwell Titan X on 6+6 power.
Been using this config for a year and a half, only one time has it ever shut itself off (in Windows, final level of Starcraft II).
I was able to use Nvidia Inspector to lower its target power to 90% (225W) and finish the game just fine after that.
Nothing else I've thrown at it fazes it, not even Furmark.
 
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My Mac Pro 5,1 has worked flawlessy with the MacVidCards NVIDIA GeForce GTX TITAN X. Mac Pro has multiple cores, multiple PCIe slots used, and one power hungry HDD - no problems. MacVidCards provided the 6-pin and 8-pin cables and again, there's been no issues of any kind so far. I think I remember reading that the GTX TITAN X draws less power than the GTX 980ti but I'm not 100% sure.

Mac Pro specs:
12-Core
NVIDIA GTX TITAN X
3 PCIe drives (OWC Accelsior E2)
1 HDD (WD Black, 6 TB)
 
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I am wondering how close to the edge my system is so I actually took the time to do the math. Well, "quick math" since I couldn't find some of the numbers so their is some very quick guess work based on a little info (I figure the numbers below are within 10-15% of being accurate):

Dual Hex 3.3 CPUs, Ram, Motherboard 300 (total guess based on other numbers I found)
GTX980Ti 250
SSD 30
PCI Single SSD 40 (I'm not sure how many watts the actual PCI card gets so I added a bit)
PCI Double SSD 75 (I'm not sure how many watts the actual PCI card gets so I added a bit)
Cool Spinning 4TB HD 10
Cool Spinning 4TB HD 10
7200 HD 12
7200 HD 12
Superdrive 50 (couldn't find any data on this so this is a total guess)


My system total 789

Total cMP power supply watts 980

So i have 200 watts extra more or less depending on my guesses above. I can live with that. Anyone have a better guess on the numbers above?
 
Murray M said:
I am wondering how close to the edge my system is so I actually took the time to do the math. Well, "quick math" since I couldn't find some of the numbers so their is some very quick guess work based on a little info (I figure the numbers below are within 10-15% of being accurate):

Dual Hex 3.3 CPUs, Ram, Motherboard 300 (total guess based on other numbers I found)
GTX980Ti 250
SSD 30
PCI Single SSD 40 (I'm not sure how many watts the actual PCI card gets so I added a bit)
PCI Double SSD 75 (I'm not sure how many watts the actual PCI card gets so I added a bit)
Cool Spinning 4TB HD 10
Cool Spinning 4TB HD 10
7200 HD 12
7200 HD 12
Superdrive 50 (couldn't find any data on this so this is a total guess)


My system total 789

Total cMP power supply watts 980

So i have 200 watts extra more or less depending on my guesses above. I can live with that. Anyone have a better guess on the numbers above?
Click to expand...

According to a PSU expert in this forum's post (few months ago). That 980 is the max rated, no guarantee that the PSU can actually deliver 980W in any situation. e.g. under high ambient temperature.

Anyway, it's hard to believe that your SSD can draw more then HDD. But, your estimate is on the safe side anyway.
 
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Have you got more than one SSD in your Mac, 30W seems a bit overkill. I've got three Angelbird SSD's in mine and, according to their tech specs, the draw a maximum of 1.97W each.

Found this chart on Tom's Hardware.
 

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I have two machines running GTX980ti. One uses a reference EVGA ti and has the 8pin/6pin connector on the card. I have been running this machine using the mini power adapters on the logic board for about a year and a half with no problems. in regular mac usesage it barely uses any power according to istat Menu. With heavy rendering it gets warm and fans spin up, but it in no way overloads the system.

My second machine has the GTX980ti FTW and this card has two 8pin/8pin connectors on the card. I initially connected it with 6pin to 8pin mini connectors like my first machine, but it didn't like it. At full bore in games, one connector was pulling WAY more power than the second. Power supply would overload and just shut off. No harm done, but not reliable. I rewired the card to use the two logic board mini connectors Y-harnessed to one 8pin, and the two SATA ROM drive plugs Y-connected to the other 8pin. In this configuration the machine runs very well. No overloading and no shutdowns. According iStat menu, the card pulls anywhere from 140-190 watts.

Now, istat may not be that reliable, but it appears that the 250-300 watt spec of the cards is for a burst spike and not a continual power draw. Your results may vary.
 
The APIs and clunky old drivers on macOS prohibit the 980Ti from reaching its highest potential anyway, so its power consumption under macOS will naturally be less than under Windows.
 
I run my FTW machine with Windows Ten. It perfoms about the same as macOS. Although I don't have a program like iStat in windows, the FPS and card temps come out about the same.
 
I have now received and installed the EVGA GTX 980ti ACX2.0+ SC+ by connecting it directly via 6pin->6pin and 6pin->8pin cables. First time I booted up, about 1min after I logged in, all the vents went crazy. All of them went all the way up to their respective max's, e.g. BoosterA/B @5200. This was not just the normal PCIE vent going up after startup which is a well documented bug. Second time, again the same symptoms, temps were perfectly fine and the systems behaved completely normal. I then used Mac Fan Control to bring the vents down to normal levels. after a bit more testing, I removed Mac Fan Control again and things seemed to be ok.
However, once yesterday, and again this morning I had a hard shutdown, preceded by a dark screen for a couple of minutes, which never ever happened before so I must conclude the card is at least sometimes drawing too much power from my older cheese grater. On the other hand I've already been doing some test rendering with THEA (CPU&GPU) which went perfectly fine and the speed is indeed something to behold. Anyway, I may go back after all to my initial idea to balance the load between the two 6pins or even go down the route of the pixlas mod.

BTW my cMP is quite fully stuffed with 4 hard drives, 1 PCIE SATA adapter with Samsung SSD, and another Samsung SSD as boot drive on the second optical SATA.
 
You may need to move some things around. I have two SSD PCIe cards and a GTX980ti in the PCIe bay. Initially I left the stock video card in for occasional boots, but found that the extra power draw made the computer think it was getting too hot and the fans were going crazy. The SSDs also showed an increase in Temp being right next the the 980. In the end, I moved the SSDs to the top two slots, left the 3rd open with the backplate off for more air out and the 980 in the lower slot. Fans performed much better. I only had to use fan control to lower the boost fan by a few 100 RPMs to get things quiet. (I also have 4 SATA drives in the bays, so I am at max power useage)

you should look into running one power plug off the PCIe mini connectors and the other power plug off the two SATA plugs in the CDROM bay. That was the magic connect for me that made everythign stable.
 
Being a SC (superclocked) card might be the problem. 980Ti are right at the threshold of what a 6+6 pin CMP can tolerate. Best to go with vanilla reference cards.
 
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