Do I need a different PSU? Gigabyte 9070 XT & Corsair RM850e
Posted by 2_wyckyd@reddit | buildapc | View on Reddit | 5 comments
I picked up a Gigabyte Radeon 9070 XT, and it looks like it requires 3 PCI Express power cords as input. The PSU I purchased, the Corsair RM850e, has three CPU/PCIe outputs, but I’m pretty sure I need two of those for the CPU itself. So I’m seemingly two wires short. Am I missing something here? I haven’t built a PC in years.
BaronB@reddit
The Corsair's PCIe cables all have two 8 pin connectors on them they can be used to connect to the GPU. A lot of people will recommend against using both at the same time, but this is because daisy chained cables like that are only required to handle 250W totally according to the ATX spec, but some Nvidia GPUs would pull over 400W from them causing issues.
Corsair's cables are over spec, and can handle around 350W.
GolemancerVekk@reddit
First of all, the PCIe spec is 150W per connector, so whether Corsair cables can do 300W or 350W is irrelevant since it's >150W either way.
Secondly, Corsair cables are the same as everybody else's, 16AWG for the main cable (suitable for carrying 300W) and 18AWG on the splitter (suitable for 150W).
Thirdly, the problem with the splitter design is that the PSU can't control what the card decides to pull through the splitter. There are 300W available and the card can decide to pull >150W through the connector that has the 18AWG cable.
The PSU manufacturers use this design to reduce costs since an 16/18AWG cable + splitter is cheaper than two 16AWG cables. They are basically covering their ass with the bare minimum and hoping that the card manufacturers follow the spec and don't pull more power... which has already been proven false (basically every single modern GPU will spike above its official TDP).
Will this cause a problem? Maybe, maybe not. Depends on how long the power draw is and on which connector. Basically you're playing russian roulette with your expensive components.
My personal advice for OP would be to return the RM850e and get an ADATA XPG Core Reactor II 850W which has plenty of PCIe individual cables and it's a higher quality PSU anyway. Probably get it cheaper too. That's what I'd do if it were my PC.
ping /u/2_wyckyd
Full-Resolution9449@reddit
It's fine. THe ports on the power supply can do two 8 pins each basically so one port will have the 8 pin for the CPU , and the other two ports could have 2 8 pin PCIE EACH so a total of 4
it looks like the cables included with it are a 1x 8 pin pcie, and a 1x dual 8 pin pcie so you should be fine
2_wyckyd@reddit (OP)
So there’s one port on the PSU that says 12V-2x6, is that what I use for the PCIe cable?
Full-Resolution9449@reddit
no that's for the 12v 12 pin connector, also called pcie HPWR, it's what the Nvidia cards have on them
I don't think the 9070XT has that so you wouldn't use that. You'd use the pcie 6+2 (8 pin) and you'd use the other pcie dual 6+2( dual 8 pin) to connect to the GPU, so that makes 3 8 pins