Sorry this is a long one, I’ll try to keep as much fluff out as possible.
Using the ASUS WRX80 motherboard and a threadripper, I built a machine for 3D rendering that had eight 3090s in it (using bifurcation cards since it has 7 PCIE slots). I’m now trying to upgrade to seven 4090s since it will be way more powerful and much simpler with having one GPU per PCIE slot.
To explain how I have the power distributed: I split 6 of the GPUs between three 1300w PSUs. Then the 7th GPU and mobo are plugged into a 1000w PSU. I have the two 6 pins in the side of the mobo plugged in as well as that is required if you have more than 4 GPUs.
The problem I’m seeing is that if I have too many cards slotted in the mobo in it will shut off before it posts. I first had a 1000w power supply (EVGA 80+ Gold) powering the motherboard and CPU, with that I was able to get 4 cards running. If I added a 5th card, it would shut off before posting. Through tinkering, I figured out if I used a 1300W power supply (EVGA 80+ Gold) for that, I was able to get 5 cards to boot into windows, but 6 cards plugged into the board would shut off before posting.
Here is what I tried so far (to no success):
- Updated the mobo BIOS
- Splitting power cables that plug into the mother board between multiple different power supplies. So CPU in one PSU, everything else in the other.
- Using 5 cards, I moved the GPU in slot #5 to #6, it booted into windows. So it’s probably not the PCIE slot
- Using what would normally be the 6th GPU as the 5th GPU (so 5 cards total still), and it booted into windows. So it’s probably not the GPU or riser cable.
Everything seems to point to a power issue, but how is 1300w not enough? The UPS the power supply is plugged into for the mobo says it’s drawing less then 500w when booting. Any help is appreciated.