Purely theoretical: Dual SFX-L PSUs to power a beast system

LePhuronn · 2 Mar 2018 at 15:21

Hey.

This is a purely theoretical question to satisfy a curiosity I have. I have very tentative plans to do a big mod project, and some of the case work I'm thinking would significantly restrict the amount of space I'd have for a PSU. Given I'd like the hardware to match the ridiculous case and modding, I'd be looking at a stupid core count on a HEDT platform with a pair of bonkers GPUs. For a reference point, let's say a 1950X Threadripper on an Asus Zenith Extreme and a pair of Asus Strix 1080 Ti.

But given the space restrictions, I couldn't use a single 1300W+ PSU to drive it all. but what about a pair of 700W SFX-L units? Again for reference, let's say Silverstone SX700-LPT.

These units only have 1 8-pin EPS each and the Zenith Extreme needs 2, so what about using 1 PSU to power both graphics cards, and the other unit runs 24-pin ATX, 8-pin EPS and rewire an 8-pin PCI-E into another 8-pin EPS?

Doable or would this just catch fire and create a £5,000 bomb?

Like I said, it's a purely theoretical situation, but if it'd be doable then some design ideas would become a little more concrete.

Anybody to chime in?

Armageus · 2 Mar 2018 at 15:25

Not an issue - it's the same thing a lot of miners have been doing to get extra pci-e connectors when running lots of GPUs.

Something like:
My basket at Overclockers UK:

1 x Kolink Dual / Multi Power Adapter for combining Power Supplies= £8.99

Total: £11.73 (includes shipping: £2.74)

will auto start the 2nd PSU for you

LePhuronn · 2 Mar 2018 at 15:47

Thanks Armageus, but you were supposed to say "no, don't do it" because now I really want to grab an In Win 909 and start chopping it up

Seriously though, some prior research has turned up people saying it's a bad idea, especially with newer units with Active PFC shutting down because GPUs will be drawing power from both PSUs, and the 2nd PSU will no no +5V load causing massive Vdroop on the 12V. Admittedly these posts were from 2012 and 2014, so is it no longer an issue?

But then we have B Negative lauding the Corsair SFX units for running together in his Mil-Spec Caselabs build (Corsair SF600 and SF450).

It's a project that will never happen, but I do like torturing myself with these things, and knowledge for knowledge's sake is always fun.

Kurgen · 6 Mar 2018 at 19:31

does do the same thing, out of stock currently

My basket at Overclockers UK:

1 x Phanteks Power Combo Device - 2 PSU to 1 Motherboard PH-PWCOB_2P1M= £37.99

Total: £48.49 (includes shipping: £10.50)

rtho782 · 9 Mar 2018 at 11:54

I have a number of mining rigs running fine with dual PSUs, some GPUs on one PSU some on the other. I have had zero issues with it, it's worked really well.

I've got a range of PSUs in use, a couple of RM1000i, a Superflower 650W unit, a no-name chineseium 1350W unit, a couple of Cougar 650W units. All or most of them will be active PFC.

LePhuronn · 9 Mar 2018 at 16:13

Good to know. Having looked at the Kolink PCB Armageus posted, it occurs to me that the 4-pin Molex on it is probably used to power that relay, so there's likely to be some kind of 5V load which would help the supposed Vdroop issue.

But, alas, all of this useful conversation has come to naught. 2 SFX-L PSUs are 250mm wide, the case I wanted to use is 231mm wide. So they won't fit side-by-side and any other potential arrangement ends up taking space I wanted to recover by not using ATX PSUs in the beginning

Thanks for all your input, it's appreciated.