Mac Pros are equipped with 2x mini 6-pin power supply socket on the motherboard. If you plan to upgrade your video card, most of the current GPUs come with 8-pin socket nowadays. How did any of you manage to find the solution for the correct power adapter cable? Any of your responses would be appreciated.
Mac Pro (Mid 2012), macOS Sierra (10.12.3), 8-Core 32GB
In running such current graphic cards with 8 pins in Mac Pros, I think the following system monitor apps could be quite useful as for safety precaution in case of excessive temperature or power draw.
These apps I stumbled upon a while ago have very good reputation in many online communities, and in my user experience provide reliable and comprehensive readings about system hardware in various perspectives. However, temperature of non-mac-edition cards are NOT displayed for any slots of Mac Pro due to the limitation of System Management Controller (SMC), but power draw in ampere (A), which can then be calculated for wattage (W), is displayed for every slots. They are essential for power workstation owners.
And as for power adapter cable, I decided to use dual mini 6pin to 8pin 18AWG cable, which is safer than using 1x mini 6pin to 8pin cable and could keep my mind at peace to some extent, esp when series of 3D rendering tasks, driving 4K resolution on two monitors, and perhaps occasional gaming for a break are involved for a certain period of time. Just to be certain, I have plan to do some intensive testing and benchmarking prior to letting this workhorse run on its race track.
If the video card requires either less than the maximum a Mac Pro can supply or only slightly more then you can get a 6pin to 8pin adapter and be fairly safe in using it. I did this as an example with an AMD Radeon HD 7970.
The maximum power a Mac Pro can supply is 75w from the PCIe slot plus 75w per 6pin cable meaning a total of 225w.
If the video card does require significantly more than the maximum the Mac Pro can supply then you need to get a secondary power supply to provide the extra power. This could be an external power supply or it could be fitted in the second i.e. empty optical drive bay of your Mac Pro. See the following article and follow the links on it.
http://www.macvidcards.com/do-i-need-an-additional-power-supply.html
Thank you for great comprehensive explanation John. My understanding is that HD 7970 is rated as TDP of 300W, which exceeds the power supply limitation of logic board (or motherboard), and yet so far running safely with 1x mini 6pin to 6pin and 1x mini 6pin to 8pin. So it is really true then – some reported that each mini 6pin can handle power draw up to ~120W max or even more perhaps? One thing for sure is that cMP's internal build-in PSU can supply the whole system up to 980W.
So for my case, Sapphire Nitro+ RX 480 OC 8GB non-reference should be no big deal at all for cMP as it is rated as TDP of just 225W, especially connected by dual mini 6pin to 8pin Y-splitter power adapter cable. Moreover, Polaris architecture is considered more power-efficient than previous generations. I wonder nevertheless, in worst case scenario, what could possibly happen to logic board or GPU at overload – just shutdown or any harm to the system?
Most of the time a video card is hardly doing any work, if however you were running it heavily for prolonged periods then this would for a card like the HD 7970 cause it to draw more than the official capacity of the cable and cause the cable and more importantly the very thin wires on the main Mac Pro logic board to heat up and perhaps fail. In my case I don't stress the card so it was a minimal risk, however if you were doing several hours of heavy gaming, or running a BitCoin mine, or some other similar stressful task it might be a risk.
On the Mac Pro the PCIe power leads go via the logic board whereas in many PCs they go direct to the power supply, this means the logic board is a potential point of failure if over stressed.
Two possible results would be either melting the logic board wires, or causing the Mac to shutdown as a preventive measure. Each 6pin connection is officially rated at 75w, like normal electrical cabling you can pull more than the official amount but this causes excess heating and potentially failure or even fire.
Note: The RX 480 apparently is only supported in Sierra so as you have a 2012 model which you can run Sierra on you will be ok.
What's the most reliable external power system? I have run 2 GTX 680 cards on a Mac Pro 4,1 with an external supply, but when I swapped them for a 780 ti, the card crackled and smoked. Does this mean the PSU is too small for that card? I'd like to know before I plug in the replacement card.
How to connect to current Graphic Cards with 8-pin in Mac Pro?
