Question How to correctly hook up power supply to WRX90E-SAGE with two GPUs ?

[jferments]

I am currently building a PC based on the WRX90E-SAGE motherboard, and I'm unclear on the proper way to hook up the power cables from the PSU. The information in the manual is very sparse, and I'm worried I'm gonna hook something up wrong and damage my hardware.... I am going to be running 2 x RTX 4090 GPUs and an AMD 7965WX CPU, and I am using an EVGA Supernova G+ 1600W PSU.

So basically my questions are:

1) For the CPU, should I be connecting the cable from PSU port CPU1 ---> CPU 12V1_1 on the motherboard? What are the other CPU ports for? (the other ports are called CPU_12V(2)_1, PCIE_CPU_12V_1, PCI_CPU_12V_2) .... Given that there is only one CPU socket on the motherboard, I don't understand why there are two CPU power ports? Also, am I correct to assume that I should be using CPU_12V(1)_1 instead of any of the other ports?

2) As far as the GPU, I am using dual RTX 4090s as I mentioned above, so I noticed this section in the manual:

When installing two or more graphics cards ensure to connect the PCIE_8P_PWR
connector(s). If the PCIE_8P_PWR connector(s) are not connected, a BIOS prompt will
appear and will remain until you have connected the PCIE_8P_PWR connector(s).

When the system is powered by only one (1) PSU, ensure to use a single rail PSU if you
wish to connect PCIE 8-pin connectors to PCIE_8P(1)_PWR and PCIE_8P(2)_PWR.

Can someone explain to me what these PCI_8P_PWR ports are doing exactly? I am not understanding where I am supposed to connect these to the PSU, and what kind of cables to use. I already have power from the PSU going directly to the GPUs (4 x 8 pin PCI --> 12VHPWR port for each card).

I only have one additional VGA slot remaining on my power supply (the other 8 are being taken up by the two GPUs, each of which use 4 x 8 pin ports). Can I just use one of the 2 x 6+2 PCIe cables that came with my PSU, and plug it into the VGA port on the PSU and then plug both of the 6+2 connectors into the PCI_8P_PWR ports on the motherboard?

Thanks!

 

[thestryker]

First of all the two sets of EPS12V connectors are for if you're using dual PSUs.

It looks like the connectors you want to use for single PSU are CPU_12V(1)_1 and CPU_12V(2)_1. The EPS12V connectors are rated at 300W so it would be advisable to plug in both just to ensure best operation as the CPU is 350W TDP.

The PCIe power connectors are to guarantee PCIe slot power as they're rated for 75W each and these are the same cables as you would connect to a video card. Now the slots won't necessarily be drawing that much, but this guarantees you have 75W available for the video cards. I'm not sure why connecting two would be necessary, but the manual sure seems to indicate it is so it'd be worth connecting them.

 

[jferments]

It looks like the connectors you want to use for single PSU are CPU_12V(1)_1 and CPU_12V(2)_1. The EPS12V connectors are rated at 300W so it would be advisable to plug in both just to ensure best operation as the CPU is 350W TDP.

So even though I'm using a single PSU, it's OK to connect both, without risk of delivering too much power to the board?

My PSU does have two CPU power ports on it, but I'm worried that if I connect both to the motherboard, it could damage something, and I don't see any guidance in the manual on how to proceed. I'm really not familiar with this sort of thing, because I've never built a system that uses this much power, multiple GPUs, etc

The PCIe power connectors are to guarantee PCIe slot power as they're rated for 75W each and these are the same cables as you would connect to a video card. Now the slots won't necessarily be drawing that much, but this guarantees you have 75W available for the video cards. I'm not sure why connecting two would be necessary, but the manual sure seems to indicate it is so it'd be worth connecting them.

As far as the power to the GPUs, I already have 4x8 pin power connectors going to each GPU (via 12VHPWR connector), so I don't understand why the card would be needing supplementary power from PCI port ...

But like you said, the manual (without explaining why) indicates it's important so I was going to go ahead and do it, but the problem I'm running into is that I've used 8 out of 9 VGA ports on the power supply for my GPU. I only have one VGA/PCI power port remaining. Is it OK for me to use a pigtail/split PCI cable from a single VGA port on the PSU and plug both of the 6+2 ends into the two PCI_8P_PWR ports on the motherboard? Or do I need to use two separate PCI cables?

 

[thestryker]

As far as the power to the GPUs, I already have 4x8 pin power connectors going to each GPU (via 12VHPWR connector), so I don't understand why the card would be needing supplementary power from PCI port ...

Every card still pulls some power from the slot (it's part of the spec), but usually it's much less than 75W for the high power cards. I have my 3080 capped at 300W the vast majority of the time and it has 3x 8-pin cables which is plenty, but it still pulls some slot power.

But like you said, the manual (without explaining why) indicates it's important so I was going to go ahead and do it, but the problem I'm running into is that I've used 8 out of 9 VGA ports on the power supply for my GPU. I only have one VGA/PCI power port remaining. Is it OK for me to use a pigtail/split PCI cable from a single VGA port on the PSU and plug both of the 6+2 ends into the two PCI_8P_PWR ports on the motherboard? Or do I need to use two separate PCI cables?

You shouldn't have any issues at all with power draw on the board with those cards so it should be perfectly safe to use the pigtail.

So even though I'm using a single PSU, it's OK to connect both, without risk of delivering too much power to the board?

My PSU does have two CPU power ports on it, but I'm worried that if I connect both to the motherboard, it could damage something, and I don't see any guidance in the manual on how to proceed. I'm really not familiar with this sort of thing, because I've never built a system that uses this much power, multiple GPUs, etc

In the manual in the 2.5 Power Connection section on page 2-14 it shows which you should use for single PSU which is where I got the connectors I mentioned from. You are at no risk of there being too much power just by connecting the cables as it will only draw what it needs. You don't want to be in a situation where not enough power is available and since the CPU has higher TDP than a single EPS12V can provide it's a good idea to play it safe and connect both.