Question Dual-power supply configuration questions

[emma_c]

I am trying to set up a multi-GPU rig (based on mining rigs) for machine learning, and it needs two power supplies. I’m using the Supermicro M12SWA-TF motherboard (it is an oversized board of SSI EEB form factor), 6 Nvidia 1080 Ti GPUs (that each have an 8-pin and 6-pin input), one 1000W PSU for the motherboard and 2 GPUs, and one 1200W PSU for the remaining 4 GPUs. I have two sets of questions:

1. The risers connecting the GPUs to the motherboard have no power inputs. Why do posts talk about powering the risers from the same PSU that powers the GPUs? The GPUs have 6-pin and 8-pin inputs that I am planning to power from the same PSU.

2. Why do posts talk about splitter cables that connect both PSUs to the motherboard? What is this accomplishing? Also, the motherboard has four power inputs, 1 24-pin and 3 8-pin. Do I need to connect all four to both PSUs?

 

[faalin]

You can read through your manual here https://www.supermicro.com/manuals/motherboard/M12/MNL-2336.pdf but yes you will have to plug in all 3 8pin cpu connectors, you can not use the 8 pin PCIe cable for these.


As for the GPU and riser, since your are not supplying power to the riser cable it is passing 75watts from the motherboard to the GPU. You are then adding a second power and ground from the other PSU which could damage the PSU, motherboard, or cards them self.

 

[emma_c]

You can read through your manual here https://www.supermicro.com/manuals/motherboard/M12/MNL-2336.pdf but yes you will have to plug in all 3 8pin cpu connectors, you can not use the 8 pin PCIe cable for these.


As for the GPU and riser, since your are not supplying power to the riser cable it is passing 75watts from the motherboard to the GPU. You are then adding a second power and ground from the other PSU which could damage the PSU, motherboard, or cards them self.

Thank you, your reply is very helpful. If we used riser cards instead of cables, would that mean that we don’t pass 75 watts from the motherboard to the GPUs, and then we could power the GPUs from a different PSU than the one powering the motherboard?