[SOLVED] PSU for a dual 3090 build?

[MoreMoneyThanSense]

My current specs:

-3950x watercooled, 2080 ti watercooled, three GTS360 rads + 10 Noctua a12x25 fans, 64 gb trident z neo RAM running at 3800cl14, two 2TB PCIe Gen 4 NVMe M2 SSDs, Seasonic Prime 1000W Ultra Titanium PSU

I plan to upgrade to a dual 3090 GPU setup - is it recommended to beef up the power supply, and if so, to what level / what might be a reasonable pick? 1200W?

 

[torbjorn.lindgren]

With the move to the 12pin connectors, the adapters appear to need 2x8pins per 12pin.
8pins can do 150W, so two 8pins + 75W from the PCIe slot = 375W..... So the 3090s are either going to be very close to power limits with their official TDP, or they're going to need multiple 12pins (and therefor, numerous 8pin PCIe each)

If they need more than two 8pins each, they'll likely need four. Which is the absolute upper end of connectors your PSU has.

Nvidia's 12-pin power connector is pretty much only going to be used on the Founder's Edition, all the third-party 3080/3090 I've seen pictures of have either two or three (higher-end cards) 8-pin connectors.

For clarity, the 12-pin connector is not inherently limited to 2x150W, it's officially rated for 600W! - the minimum quality of pins and cables are that much better! This is why Seasonic suggests a minimum of 850W PSU for their modular 12-pin cable intended for their existing modular power supplies (IE Seasonic made sure it can handle 600W).

Now, the 2x8-pin->12-pin converter that Nvidia provides in the box do technically only have 150+150W "available" as rated by the PCI-E consortium, though it's well known that the 6/8-pin ratings are extremely conservative - der8auer did some testing a while back gradually reducing the number of cables to test how conservative and the answer was "insanely conservative". I wouldn't be the slightest surprised if the converter and a decent (or good!) PSU would be fine handling the full rated 600W via it as long as the two 8-pin connectors isn't sharing a single cable to the PSU!

Not that I expect that it'll be possible to make a 3090 card to pull that much (500W+) anyway without resorting to at least chilled water cooling if not LN2 overclocking, and cards intended for that definitely is going to either be powered via 3 (or more) 8-pin or a very beefy PSU with sufficiently beefy cables for the converter (if it's a FE card) to be a non-issue. Yes, this assumes no cable sharing but when we're talking high-end overclocking that's just another way of saying "don't sabotage your own build"

 

[Barty1884]

Now, the 2x8-pin->12-pin converter that Nvidia provides in the box do technically only have 150+150W "available" as rated by the PCI-E consortium, though it's well known that the 6/8-pin ratings are extremely conservative - der8auer did some testing a while back gradually reducing the number of cables to test how conservative and the answer was "insanely conservative".

Yes and No. On a quality unit,no doubt about it - as all cables will be a minimum of 18AWG.

IIRC though, the ATX standard doesn't specify AWG requirements - So something like 20 or even 22 AWG could be used by some cheaper units. Theoretically capable of the >150W for an 8pin PCIE connector..... At (something like) 50'C. In practice, 150W would be the absolute upper end you'd ever want to see.

So, releasing a product that runs out of an existing spec (ATX2.31*) is a complete no-go.

*And 2.31 is still the 'latest', >10 years after release

I wouldn't be the slightest surprised if the converter and a decent (or good!) PSU would be fine handling the full rated 600W via it as long as the two 8-pin connectors isn't sharing a single cable to the PSU!

Same as above really.
8pins are standardized to 150W. Whether multiples of 8pins directly, 8pins adapted to 12pins single cables or daisy-chained off one, the standard exists.

Not disputing a quality unit can output substantially more.... and there's much more available provided you're not daisy-chaining off a single cable - The fact is, the standard doesn't change for a new product. If the card needs 500W (for arguments sake), it needs three 8pins (+75W PCIE) at an absolute minimum. Recommendations can be for separate cables for each 8pin etc within the product marketting etc, but daisy-chained 8pins should 'just work'.

 

[Karadjgne]

It's all in the pins and plastic. The pcie pins used have a rating of 5A, there's 3 hots in an 8pin pcie, so can theoretically use upto 180w before becoming too hot and melting the connector. Same for the 6pin, has 2x hots so is good for upto 120w theoretically. But, that's Molex connector standards, there's other companies out there that make cheaper substitutes and use less heat resistant casings, so the 75w/150w standard was applied to the gpu itself. But it's common for vendors to fudge that a little at times, even AMD was pulling over 90-94w from the x16 with initial releases of the Rx480's, physical limits of That slot are supported 100w. And that's not including the AMD 450w+ power draw from the R9 295x2, which had spikes exceeding 600w.

Wouldnt be all that difficult to have a 12pin pulling 600w, just requires a change in connector to the 9A or 11A version pins/connector, the 11A version only using 5x hot leads, the 9A version using 6x

Physically, a 12" section of 18ga is good for 10A @ 12vDC continuous. Or about 7A for a 18" section. So each 18ga hot is physically good for @ 100w± at 18" or 132w ± at 12". Plenty of space for upgrade to higher rated pins.