extra pcie power on motherborads (TR4)

[Pesky Ngon]

ive noticed some mobos have a 6pin on them for extra PCIE power. i plan to have between 5 and 8 Navi GPUs attached to a TR4 mobo for 3D rendering work. obviously this is going to draw a lot of power. 

i will probably be combining two 1600w PSUs to get enough power for the GPUs. can someone please explain the relevance of the extra 6 pin for PCIE power? will it cause me any problems if i dont have one on the motherboard i buy? im thinking of things like instability, killing components, shortened life span, lower performance etc. you get the point. would greatly appreciate any help.

[GoldenLag]

Well if you are going to do 8 cards you will need a passive PCIe splitter. 

 

As long as you plug into the GPU directly it wont be an issue. Boards that need extra PCIe power will say so in the manual or have extra power inputs.

[Pesky Ngon]

2 minutes ago, GoldenLag said:

Well if you are going to do 8 cards you will need a passive PCIe splitter. 

 

As long as you plug into the GPU directly it wont be an issue. Boards that need extra PCIe power will say so in the manual or have extra power inputs.

im not planning on using a pcie slitter, it would limit bandwidth too much (1x). im planning on having 5 gpus in the pcie slots (16,8,16,8,4), but most (tr4) boards have 3 nvme slots. i can use an adapter on each of these to plug one more gpu in per nvme slot at pcie4x each.

[jj9987]

That plug is needed if you have multiple cards that draw (a lot of) power from the PCI Express' slot. In that case you may run into issues with power delivery, if the cards pull power from the socket. If the plug is there, connect it. If the plug isn't there, I wouldn't worry about it unless you run into issues (instability).

 

Some graphics cards pull all the power from the PCIe power connectors, some pull most power from that, but some from the socket (for less power consuming parts, for example memory).

[GoldenLag]

6 minutes ago, Pesky Ngon said:

im not planning on using a pcie slitter, it would limit bandwidth too much (1x). im planning on having 5 gpus in the pcie slots (16,8,16,8,4), but most (tr4) boards have 3 nvme slots. i can use an adapter on each of these to plug one more gpu in per nvme slot at pcie4x each.

You get 16x to 2 8x adapters......

 

Would be lot less of a mess than to use the m.2 ports

[Jurrunio]

The 24pin can easily supply 150w to the PCIe slot (technically 3 cards is possible, but that's pushing the two wires hard). The 6pin, when going out of ATX spec but within that of the wires, can push 300w per daisy chained cable (yes, even if you only use one of the plugs on the cable) and that's enough for at least 3 cards. Those connected through M.2 slots will need extra power plugs to the adapters so they arent calculated here.

 

Note that I take 75w per card as that's the ATX spec for 12V and 3.3V combined (though minimal from 3.3V). Different cards manage power connections differently, some use less than others.

 

If you dont use a board with extra PCIe 6pin for PCIe slot power (not even the stupid molex on Asus X399 is enough), you'll burn the 24pin and that's game over.

[Pesky Ngon]

19 minutes ago, GoldenLag said:

You get 16x to 2 8x adapters......

 

Would be lot less of a mess than to use the m.2 ports

hmmm true....or...i could use both and get 10 cards? :'D 

[Pesky Ngon]

22 minutes ago, Jurrunio said:

The 24pin can easily supply 150w to the PCIe slot (technically 3 cards is possible, but that's pushing the two wires hard). The 6pin, when going out of ATX spec but within that of the wires, can push 300w per daisy chained cable (yes, even if you only use one of the plugs on the cable) and that's enough for at least 3 cards. Those connected through M.2 slots will need extra power plugs to the adapters so they arent calculated here.

 

Note that I take 75w per card as that's the ATX spec for 12V and 3.3V combined (though minimal from 3.3V). Different cards manage power connections differently, some use less than others.

 

If you dont use a board with extra PCIe 6pin for PCIe slot power (not even the stupid molex on Asus X399 is enough), you'll burn the 24pin and that's game over.

thanks for the info, very helpful  

[GoldenLag]

2 minutes ago, Pesky Ngon said:

hmmm true....or...i could use both and get 10 cards? :'D 

You could do 16x to 2 8x to 4 4x.

 

You dont really beed more than 4x if its PCIe 4.0 and threadripper 3k