Is it OK to power an RX 580 with a molex to 8-pin adapter?

pyronautpyronaut Member Posts: 3
I just bought a 6th card for my rig, but my PSU (EVGA SuperNOVA 1000 G3, 80+ GOLD, 1000W) only has 5 8-pin GPU cables. It has a spare cable with 4 molex connectors on it, however (the part plugging into the motherboard is 6-pin, but two if them are hollow).

I was wondering if I can just get a 2 molex to 8 pin adapter and use that to power the card instead. I've heard that each molex can handle 40w, which would make 80w total, but the card will probably pull between 90w and 120w depending on the mod, so I'm not sure if the molex adapter will be up to the job.

What do you guys think? I want to avoid having to buy another PSU if I can, since I'm trying to reduce costs/ROI time. I'm using 760W at the wall, so the PSU has plenty of juice left to give.

This is the adapter I'm thinking of getting:


The other option is to use the GPU cables that split into two 8-pin connectors. Since I'm under-volting my current cards to 90W and one 8-pin should be able to handle 300W, I think I should be able to use one GPU cable to power two cards.

Comments

  • TaltonTalton Member Posts: 25
    There are a bunch of different accessories you can get for PCIe 6 / 8 pin splitting, check a few out here: https://www.amazon.co.uk/Startech-com-Express-Power-Splitter-Cable/dp/B004NNTVT6/ref=sr_1_5?ie=UTF8&qid=1516744388&sr=8-5&keywords=PCIe+8+pin+splitter

    I'd personally have a little play around, if you're splitting power from one cable to another then you've not really got any worry of over volting, it's when you're putting 2 powered cables into 1, that's when I'd worry.
  • pyronautpyronaut Member Posts: 3
    Thanks for the info. With the above adapter I'd be putting 2 molex connections into one 8 pin, but since molex carries less power than 8 pin I don't think there would be an issue.

    I think the better option would probably be to use the cables that already have two 8 pins on the end though. I just wasn't sure if it could power two cards, but from what I've read it looks like it should be able to handle it. I just wanted to make sure I didn't have bad info before going with that optin.
  • rmhrmh Member Posts: 410 ✭✭✭
    edited January 2018
    pyronaut said:

    Thanks for the info. With the above adapter I'd be putting 2 molex connections into one 8 pin, but since molex carries less power than 8 pin I don't think there would be an issue.

    I think the better option would probably be to use the cables that already have two 8 pins on the end though. I just wasn't sure if it could power two cards, but from what I've read it looks like it should be able to handle it. I just wanted to make sure I didn't have bad info before going with that optin.

    It depends on the GPU, but this converter will fry for example on an R9 390X.
    For safe PCI-E 8pin powering from molex/sate, you should do this:
    2x molex=>1PCIE 6pin
    2x molex=>1PCIE 6pin
    2x PCIE 6pin => 1 PCIE 8pin
  • pyronautpyronaut Member Posts: 3
    edited January 2018
    rmh said:

    pyronaut said:

    Thanks for the info. With the above adapter I'd be putting 2 molex connections into one 8 pin, but since molex carries less power than 8 pin I don't think there would be an issue.

    I think the better option would probably be to use the cables that already have two 8 pins on the end though. I just wasn't sure if it could power two cards, but from what I've read it looks like it should be able to handle it. I just wanted to make sure I didn't have bad info before going with that optin.

    It depends on the GPU, but this converter will fry for example on an R9 390X.
    For safe PCI-E 8pin powering from molex/sate, you should do this:
    2x molex=>1PCIE 6pin
    2x molex=>1PCIE 6pin
    2x PCIE 6pin => 1 PCIE 8pin
    Yeah that's what I was worried about, so that's why I was leaning towards the 8-pin splitter cable that my PSU came with instead of molex. It should be able to handle two cards from what I've read about 8-pin cables.
    Post edited by pyronaut on
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