Safe to power risers with secondary PSU?

hellohahelloha Member Posts: 18
I'm running short on molex and sata plugs on my psu. I do have another one that I could use just to power the risers. Is this a good idea?

Last week I had two dead cards and I am still trying to find out what happend. I have a riser that acts funny and has two burned out solder joints at the bottom. This could be the cause or else it was due to combining PSU's (the PCIE power) (don't do this!).

Wondering is only powering the riser is safe or not?

Thanks!
K.

Comments

  • hellohahelloha Member Posts: 18
    FYI: ALWAYS TEST YOUR RISERS ON CHEAP HARDWARE!
  • Techman34Techman34 Member Posts: 405 ✭✭✭
    @helloha this has been the subject of much debate! Here's a succinct excerpt from an old thread from @Heliox who said:

    "PSU that powers the motherboard also powers my primary graphics card, so PCI-E 16 slot closest to the CPU.
    It as well powers my second one (the second PCI-E 16 slot "if the mobo has one").
    My PSU that powers my motherboard also powers all of the risers.
    So my secondary PSU only supplies power to the additional graphics cards. Not their risers."

    Extensive debate has gone on, but much of the PCI-E technical spec was explained by @mmx so he provided the science behind why the method here is the right one. So bottom line is PSU 2 should only be providing extra power to the top PCI-E VGA power connection on the top of the extra GPU's.
  • hellohahelloha Member Posts: 18
    Thanks, I'll do some more reading in those posts, and stick to adding PCIE power directly on the card itself from the second PSU.

    FYI: here's what a faulty riser looks like:


  • charliebridge82charliebridge82 Member Posts: 34
    Techman34 said:

    @helloha this has been the subject of much debate! Here's a succinct excerpt from an old thread from @Heliox who said:

    "PSU that powers the motherboard also powers my primary graphics card, so PCI-E 16 slot closest to the CPU.
    It as well powers my second one (the second PCI-E 16 slot "if the mobo has one").
    My PSU that powers my motherboard also powers all of the risers.
    So my secondary PSU only supplies power to the additional graphics cards. Not their risers."

    Extensive debate has gone on, but much of the PCI-E technical spec was explained by @mmx so he provided the science behind why the method here is the right one. So bottom line is PSU 2 should only be providing extra power to the top PCI-E VGA power connection on the top of the extra GPU's.

    That's exactly the way I'm doing things: 2 rx470 and 3 rx480, all powered by one HP 750 server psu (6/8 pin connectors), the risers, mobo and ssd are powered by an evga 650BQ. The risers are powered with "hand-made" cables, since the sata-molex adapter doesn't have the capacity to withstand the power demand of a 470/480 gpu.
  • hellohahelloha Member Posts: 18
    So I used the setup where I power all the risers from the PSU that is connected to the motherboard and all seems to go well. Additional PSU's only provide PCIe power directly to the card over 6-8 pin cables.

    Now I am planning to add a M.2 PCIe riser to add an additional card. My question: these adapters also have 4 pin connector and a molex adapter. Any idea what to do whith this?

    Also connecting to this M.2 riser is a normal PCIe riser that is already powered. Should I even bother powering the M.2 riser again?

    Thanks for any advice!
    K.
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