Sidebar Sidebar
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.

MP 1,1-5,1 RX6800 (non-XT) for 5,1 - Dual 8 Pin power without Pixla's ?

C

crackajacka77

macrumors newbie
Original poster
Jun 3, 2022
18
1
Hey there,
currently using an external PSU for powering my RX6800 in the 5,1. Is it possible to get dual 8 pin power from the stock 5,1 without going into doing the Pixla's mod?

Thanks!
 
Last edited:
Not without doing it safely. You will burn or at least get the Mac into emergency shutdown, when you overload the PCIe additional power rails >> 100 Watts, each.

There are attempts to get a few watts from the Sata ports, this is not the way to go.
 
  • Like
Reactions: d0sed0se
Hey Macschrauber, poking cables in the 5,1 power supply also doesn't sound that safe to be honest :)
 
If you can't do it yourself, ask a friend that knows how to do it or go to a qualified technician.

Is the only way to safely install a GPU with more than ~200W power draw inside the MacPro5,1, powered by the internal PSU.
 
  • Like
Reactions: d0sed0se
Yeah, if there's anyone able to do Pixla's mod here in Berlin, please feel free to hit me up. Otherwise I'll just gonna stick to the external PSU. Thanks again you two. 👍
 
crackajacka77 said:
Yeah, if there's anyone able to do Pixla's mod here in Berlin, please feel free to hit me up. Otherwise I'll just gonna stick to the external PSU. Thanks again you two. 👍
Click to expand...

Mac Factory is in Berlin. I dont know how good they work, but they sell a lot of Mac Pro parts and machines.
 
hey there, i'd recommend trying the evga powerlink with your RX 6800. from what i've seen on google, max wattage is 250w, which is technically over spec but i'd be surprised if the mac shut down from that tiny bit of extra power draw with the evga power link. you should run a gpu benchmark or something that really utilizes gpu resources (davinci effects or cinema4d) just to test

edit: bear in mind that RX 6800 won't work in ventura or sonoma (monterey at the latest), as OCLP team is working to patch those drivers still in ventura and sonoma
 
Last edited:
grandosegood said:
hey there, i'd recommend trying the evga powerlink with your RX 6800. from what i've seen on google, max wattage is 250w, which is technically over spec but i'd be surprised if the mac shut down from that tiny bit of extra power draw with the evga power link. you should run a gpu benchmark or something that really utilizes gpu resources (davinci effects or cinema4d) just to test
Click to expand...

This is just plain wrong. TDP is thermal design power and not a measure of total power draw and does not even account for spikes that will make the SMC shutdown the PSU.

While the plain non-XT RX 6800 was not tested with in same minimum details, a RX 6800XT that have a declared TDP of 300W - instead of the 250W of the plain RX 6800 - can have spikes of 433W with OC modes and 366W with the stock config:

AMD Radeon RX 6800 XT and RX 6800 Review: Nipping at Ampere's Heels

AMD's best GPUs to date are strong in rasterization but fall behind in ray tracing.
www.tomshardware.com www.tomshardware.com

Multiple people here on the forum had SMC emergency shutdowns even with even a plain Sapphire Pulse RX 580, that have a declared TDP of just 185W…
 
Please rethink this... This is a terrible idea and you will for sure burn out your backplane 🤦‍♂️
 
Most research and literature I’ve seen says you technically get 75 W from the PCIe lane, and 75-100W per six pin cable, with some reports saying you can go a little more. An RX 6800 (non XT), can pull somewhere around 250w, Which is just a tiny bit over. Yes, pixlas directly to the power supply would be best, and I even seen the video of the guy doing the mod without the vampire taps.
 
grandosegood said:
Most research and literature I’ve seen says you technically get 75 W from the PCIe lane, and 75-100W per six pin cable, with some reports saying you can go a little more. An RX 6800 (non XT), can pull somewhere around 250w, Which is just a tiny bit over. Yes, pixlas directly to the power supply would be best, and I even seen the video of the guy doing the mod without the vampire taps.
Click to expand...

Wrong again in multiple levels.

First thing, maybe someone that never rendered anything with the GPU, have just one display connected can make it work with it just being powered with the backplane, but you can’t extrapolate a video on Youtube for all use cases…

Second thing, modern GPUs never draw anything near 75W from the PCIe slot, see reference AMD RX 480 melting PCIe slots, it’s more like 40W on the graphic over time and and the AMD firmware have a hard limit with the PWM controller, even with most crazy OC modes, to never ever draw more than 71W from the PCIe slot since the RX 480 fiasco.

Third thing, if you read the article that I’ve linked you would know that the instantaneous power draw spikes are the problem, with 231W instantaneous power draw from one of the 8-pin connectors. Again, even a Sapphire Pulse RX580 in some use cases can make the SMC do an emergency shutdown and that is with a TDP of only 185W, not the 250W of the RX 6800/300W for the RX 6800XT.

TDP is not power draw, is thermal dissipative capacity and the GPU have multiple different power planes that have very different power draws overtime accordingly with what the GPU is working on. No GPU design draws 75W here, 100W there and there - modern GPUs were never designed this way and this never happens on real life.

Anyway, you are free to meltdown your own 12 to 15 years old backplane to a crisp.
 
  • Like
Reactions: ddhhddhh2 and grandosegood
hey thanks for your detailed information. i was unaware that even an rx 580 card could cause such a shutdown. if anything, i would have hoped they overengineer and allow for a bit more power draw.

i have been running a radeon vii with a evga power link in a mac pro 4,1>5,1, which is clearly over the limits, but i was always afraid to splice directly into the wires, or solder something to the psu itself. i seen this guy on youtube connect an 8 pin pcie connector directly to power supply connector going into the motherboard

(part 2 explaining the 8 pin connector)

has anyone tried this? inside the motherboard connector are these gigantic pins, so i'm wondering how well a solderless connection works? it appears to use female pcie power pins that are slightly crimped at the end with plier, according to the videos. thanks again.
 
grandosegood said:
hey thanks for your detailed information. i was unaware that even an rx 580 card could cause such a shutdown. if anything, i would have hoped they overengineer and allow for a bit more power draw.

i have been running a radeon vii with a evga power link in a mac pro 4,1>5,1, which is clearly over the limits, but i was always afraid to splice directly into the wires, or solder something to the psu itself. i seen this guy on youtube connect an 8 pin pcie connector directly to power supply connector going into the motherboard

(part 2 explaining the 8 pin connector)

has anyone tried this? inside the motherboard connector are these gigantic pins, so i'm wondering how well a solderless connection works? it appears to use female pcie power pins that are slightly crimped at the end with plier, according to the videos. thanks again.
Click to expand...
They are not locking up so definitely not recommended. There has to be a solid connection.
 
You must log in or register to reply here.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.
Top Bottom
Back