Quote from: shan23 on January 25, 2018, 11:16:16 PM

Quote from: pbfarmer on January 24, 2018, 04:38:56 AM

Quote from: shan23 on January 19, 2018, 09:46:56 PM

I'm a new comer to the forum, and I'm trying to get one last bit of info before I can assemble my 8 GPU rig. I was hoping you could answer my query regarding a similar setup.

I'm planning a 8 GPU build, in which I've ordered the following components:

2 x EVGA SuperNOVA 850 Titanium PSU
8 x GTX 1070 Founders Edition
Risers (6 Pin 006c as recommended in the wiki https://www.reddit.com/r/EtherMining/wiki/hardware/risers)

Here's a pic of the connections available in my PSU:

What I'm confused about is which slots do I connect the risers? I feel I have the following options:
1) Use a PCI-E splitter, so that each VGA slot is used by 1 GPU and its riser (got the idea from your aforementioned post)
2) Put each GPU in its own VGA slot, and its corresponding riser in a 6 pin slot in the same PSU (will have to use up a VGA slot for the third GPU)

Option 2 limits me to 6 GPUs in this rig, though my mobo is capable of 8 (z370-A). I'd obviously like to have a 8 GPU setup, but I don't want to use an option that is remotely unsafe. Am I being too paranoid about the whole thing (u can tell I read the Risers section in the wiki quite a few times!) ?

A cable w/ an 8 pin termination should be able to supply 150W according to the PCIE spec - if your GPU is drawing less than 150W, you should be able to split such a cable between the GPU and riser. The better option would be to simply use an 8+6 split (Y) cable - 8 pin to the GPU, and 6 pin (w/ an extender if necessary) to power the riser. That way you can be certain the cable is rated for that load (an 8 + 6 termination should supply 150W + 75W per PCIE spec,) assuming your cards draw less than 225W (which they absolutely should for mining.) Since you only get two of those types of cables w/ your chosen PSU, you could use the 2 x 4 pin peripheral (a.k.a. molex) cables to power your other 2 risers.

A couple other notes:

1. The draw on an 8 pin termination of a PCIE cable is spec'd to 150W, but the cable likely can provide closer to 180W (3 hot pins @ 5a x 12v or 60W each,) while the supply is actually probably closer to 240W (4 hots x 60W,) so you're probably fine just splitting a single 8 pin terminated cable if GPU TDP is < 180W. But if you want safest, the config above works (and saves you from buying additional splitters.)

2. The FUD around sata power is a little overblown. While a sata power connector easily provides the 75W max allowed for a PCIE x16 connector, the main concern is that the PCIE spec allows for 5.5a over the 12v rail (66W) on the MB connnector, while a sata power cable only provides 3 12v pins @ 1.5a each, or 12v @ 4.5a (54W) total. However, most modern, optimally tuned GPUs run around 75-150W for mining, so a single 8 pin PCIE power cable likely provides all the 12v power the card needs, w/ the MB connector/riser providing the 5v, and minimal (if any) 12v. Of course, this split is up to the GPU manufacturers, and they *could* technically pull all available (66W) 12v power from the MB bus before utilizing the PCIE power cable (or split as evenly as possible across the 2 sources,) but that is not how I've seen power delivery implemented on any recent card I've used. My cards all run in the 100-150W range, and the ones using risers powered by sata cables are doing just fine.

3. Ver 006C is pretty old for the risers. I would recommend at least ver 008s, like these: https://www.amazon.com/EXPLOMOS-Graphics-Extension-Ethereum-Capacitors/dp/B074Z754LT

Thanks a lot for the detailed reply - I learned quite a bit from it, and have ordered the 008 risers as per your recommendation!

Two follow-up queries:

You mentioned I could use 2 x 4 peripheral cables (molex) to power the other two risers (ones which aren't connected using risers). Did you mean that I use each of the 8 pin CPU ports in my PSU (marked as CPU1 and CPU2) for 2 molex cables (referring to the back of my PSU whose pic I've linked before)? If not, I don't see any more ports that are capable of handling the 4 pin Molex's?
I'm trying to get identical power inputs for each of my GPUs - so, I'm considering buying 2 more Y splitters ( 8 + 6 split(Y) to 8 pin) so that each of my 4 GPUS and its corresponding risers are powered using the Y cables. Is there anything wrong with that idea, other than the fact I'll have to order extra splitters? Speaking of which, I should be able to purchase EVGA splitters from the manufacturer's website, right, or would any amazon Y splitter would do?

Thanks!

Sorry for the late reply - hopefully you've already gotten your answers by now, but just in case...

1. sorry, for some reason I thought I saw 2 perif ports on that PSU - looks like it only has one. You should have a cable w/ multiple 4 pin peripheral (molex) adapters for that port. So you'd have to either chain 2 cards on a single perif cable, use one perif and one sata cable (assuming your card pulls less than 4.5A from the risers 12V,) or buy additional PCIE cables. You can't just use the CPU ports - those are wired differently. There are converter cables on ebay/amz, though you have to make sure you're getting the ones that are CPU->PCIE, and not just PCIE extenders (double check the wiring yourself - I've read reviews that make it sound like the wrong item gets shipped sometimes.)

2. Nothing wrong w/ using all 8+6 cables - def the safest option, assuming you're under ~225W per card. You can't purchase individual cables from EVGA - they only sell bundles, which are ridiculously expensive and you get a bunch of crap you don't need. You can get aftermarket ones from places like moddiy or cablemods (https://store.cablemod.com/configurator/) Generally, you can't get these from amzn, as the supply side termination is unique to the PSU manufacturer.