Could this PSU power an r9 390, or is the card itself to blame?

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fome33

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Jan 26, 2016
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Computer Specifications:
Motherboard: MSI Z97 PC Mate
CPU: i5-4690K
GPU: MSI R9 390 8 gigs
RAM: really nondescript, from an older prebuilt, runs fine
HDD: Seagate baracuda 2tb
Optical drive: also nondescript, mostly not used
PSU: EVGA Supernova 750b NEX
Watercooler: LEPA Aquachanger 240mm

So, I've hit a predicament. I have an EVGA supernova 750B NEX as a power supply. It has powered my last build that had a 770 just fine (and I've switched back to that card because the MSI r9 390 worries me). It has four rails with 20 amps each, with a total of 750 watts coming from the power supply. However, my computer tends to crash when the 390 comes under heavy load such as when I run 3Dmark, or Furmark, or Skyforge, or even CS:GO for a some time. A complete restart, no BSOD. Fans go out, lights go out, and then the whole thing comes roaring back to life ready for another round. Furmark doesn't even get to start before the computer shuts down. Now here's the thing, I ran the 770 on the PSU just fine on furmark with no crashes, along with Skyforge. I plan to RMA the card, but I am open to advice on what I should really do.
 
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turkey3_scratch


Multi-rail designs are not worse than single rail. If anything, they are safer, because it takes a lot less amps for overcurrent protection to kick in. Something could be burning and overcurrent protection won't even kick in on high-wattage single-rail units. The benefits of a single 12V rail compared to multi are rare, but it all comes to how well the...
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turkey3_scratch

turkey3_scratch

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If a PSU could not deliver enough power, either the PSU would catch fire or, what usually happens, is over current protection (if it's delivering too many amps on a particular rail) or over power protection (too much power being drawn as measured from the wall) will kick in and shut down the PSU.
 
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fome33

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Jan 26, 2016
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What concerns me IS the multi rail PSU. I'm not sure if I should only count the amps and watts from a single rail or go by the combined or otherwise. If it goes by individual rails, this could easily not supply enough amps for the card as I've heard it needs about 30 amps, but each of the single rails outputs 20amps each so, it wouldn't be able to even handle the card at peak load
 
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turkey3_scratch

turkey3_scratch

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Multi-rail designs are not worse than single rail. If anything, they are safer, because it takes a lot less amps for overcurrent protection to kick in. Something could be burning and overcurrent protection won't even kick in on high-wattage single-rail units. The benefits of a single 12V rail compared to multi are rare, but it all comes to how well the multi-rail is designed. Which cables have power derived from which rail. If you have a multi-rail design that puts all the PCIe cables on a single rail, that is bad, but ones that are well distributed and have a good amount of amps on their rails are, if anything, better than single rail designs.

Though single-rail seems to have taken over the market. There is marketing everywhere that "single rail is better". It's just easier to screw up multi-rail than it is single-rail, that is all. Realistically, in a multi-rail design, in order to stay consistent with the IEC 60950-1 rules, no conductor should carry more than 240W. So 20 amps should be the overcurrent protection limit on a multi-rail design, but we often see 30 amps on rails. The trick is that they use the idea that a rail delivers its current about multiple wires, not one, so if you have 4 wires delivering 12V current, it would take 960W or 80 amps for overcurrent protection to shut it down. That would be in a single rail design rated at 80 amps on the 12V rail.

But this doesn't stop the fact that the possibility exists for one wire to just-so-happen deliver 480W, which is too much, and not shut down because that group of worse did not carry a combined 960W. The result is a burnt conductor.
 
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