3080 power requirements

[Trypt]

Hello all, please take a look at my sig for the setup. I'm in the process of finally securing a 3080 (EVGA Black), but have a couple questions about the power. I have read that the 3080 wants the two 8pin connectors to come from its own cable for each, this seems to come directly from NVidia, but this makes no sense to me and indeed I have read articles that claim this is BS and that a single cable with 2 8-pin connectors from a good PSU brand will have absolutely no trouble with that.

Secondly, I will be using the 3080 for gaming of course, but also for mining during all other times, and would like to keep the Vega 56 for mining in the background as well. I will have to get the cooling under control, I know this, but how about the power?

I have the 750W Corsair PSU, it's about 1.5 years old and in great shape. The Vega 56 takes about 150W constantly while mining, so I figure with the 3080 taking about 320W max (I could always limit it at that anyway), that should be more than enough headroom especially since I don't have HDD's or anything else internally, just the two M.2s and the 3600X.

If I could get an answer for both of these questions that would be great. If the answer to the top is I need 2 separate cables but the bottom that the PSU is enough, can I run 3 separate cables (1 for the Vega 2x8pin, 2 for the 3080 one 8pin per cable)?

I guess that's three questions.

Regards

 

[don256us]

In terms of using two totally seperate 8-pin connectors: I can't think of a good reason why it would matter. Back when I started getting into PC's, we were being sold on 2, 3 and even 4 legs(?). Today's PSU's only have one. With that in mind, if you have a two cables with one 8-pin or one cable with two 8-pin connectors, they all come from the same leg.

 

[Janus67]

People have reported instability and such with using all from the same cable, to the point that pretty much all documentation for the cards specifies what cables to use. If it is 3-plug (like my FTW3s are) then two can be daisy chained and 1 obviously from a different plug/cord.

I agree with you Don, most decent PSUs these days are all single rail, I am not knowledgeable enough to know if there's anything else that goes on behind the scenes for power than that.

 

[Trypt]

I've read some posts that it's not so much about the PSU itself but about the cable. That they make the recommendation due to the fact most cables are cheap and can only handle so much current. It's precaution it seems, but I can't be sure. It seems that power delivery is not an issue, but putting 300W through one cable rather than two could be a heat issue.

 

[EarthDog]

Only one way to find out...

 

[don256us]

Rail! That's the word I couldn't remember. Thanks Janus. With only one rail, I don't see how it would matter where the plug comes from. All of the plugs are on the same rail. Now there may be issues with bad power supplies. Either poor quality, not enough power or ageing out maybe but how many legs you use per rail just can't be an issue in my way of thinking.

- - - Auto-Merged Double Post - - -

Starting to look at the power requirement for both cards. Just the 3080 alone takes 350W and Nvidia recomends a 750W PSU for a computer with just that one card. Based on limited (read: Not thorough) research, The Vega takes 236W and AMD recommends a 550-600W PSU.

Using very round and very conservative numbers, the two GPUs could need ~600W plus another 200-300W for the rest of the computer. That would reasonably put you into the 850W range.

 

[EarthDog]

The main concern here is the amount of power going through a single cable. By spec, 8-pin PCIe is 150W. A 3080 is a 320-350W card so you're running the cable/connectors out of spec at stock speeds (imagine overclocking). Typically this doesn't harm anything, especially on a quality PSU, however it is, technically, out of spec. Hence why NV recs that you use two. Will one work? Surely. But I would keep an eye on the cable under load and see how warm it gets during long heavy loads.

The concern with the rail(s) can be valid if you have a TRUE multi-rail PSU and that one of the rails doesn't have enough headroom to supply power. But since most don't that is only an issue with those units.

RE: Power use, he mentioned that his use (mining) consumes 150W on that Vega card. Plus another 320-350W for the 3080 (EVGA lists 320W for the version the OP is getting), and then another 150-200W for the system (more than 200W is too much fat on the bone) and he's still under 700W. I'd do it, happily, but there are others who find that to be too close to the max.

Using math with less fat on the bone, I don't think there is any harm in trying with what you have. But I would keep an eye on a single power cable and see how that works under extended playing time. If you have power issues under load, I would look into getting a more powerful unit for this task. 850-900W should be plenty. Do you have a Kill-A-Watt meter? If not get one. It's worth it to see how much the system pulls from the wall.

 

[Janus67]

FWIW, my two evga FTW 3080s I've undervolted/underclocked and sit between 230-250W under load when mining. When I go back to playing games or whatever I put it on defaults/auto so goes back up to around 300-325W

 

[Trypt]

Thanks Earthdog and Janus, that's what I was looking for. Indeed I will make sure I have a high quality cable that can handle the 300W, or 150W per 8pin connector. They are out there, I have seen them as aftermarket options for the Corsair PSUs (Corsair itself claims their cable can handle it as well, but NVidia disagrees).

Like I said, the Vega 56 takes about 160W while mining, and the 3080 will take max 300W, probably less. Remember that while mining, the system won't be doing anything else, I won't be mining while using the system for gaming, or at least I won't be mining with both cards while using the system. I don't see myself getting anywhere near 650W real power draw, even if I was to mine both cards and watch media for example, but I wanted to make sure by asking here what you guys think. There may be a peak here and there where the CPU actually goes to 90W for a second while the cards are taking 450W, but even that will only bring the power to 80% of 750W.

Anyway, I'll try it and see how it goes.

To tell you the truth, I may just sell the Vega 56, the only reason I use it now is cuz it's a pain to change the setup and get the RX580 back, I have two of those in the secondary system, both far quieter and same power draw than the Vega, and the 10% performance increase in the game I play wouldn't be noticable. The noise that card makes is absolute crazy, like a jet engine or something, and I have it at 40% fan speed (at 35% it's actually pretty quiet but my mem temp goes to over 90C and I don't like that for 24/7, at 40% it's at 70C GPU and 83C memory, that is acceptable). The only solution to the fan noise was to just lock it at 40%, at least then it doesn't whine up and down constantly, making it 10x worse. Now it's like a background constant hum, got used to it.

 

[dfonda]

The theoretical with one rail is that it should not matter...The reality of my two GPU's with 1000W PSU running fah was that it did matter...

Until I used separate cables they were not stable. I used one separate 8 and two 8's off the same cable on the RTX3080 and that wasn't good enough. I added a 3rd separate 8 and the 3080 ran stable.

The RTX 2060 was on its own cable and that ran stable.

I have been on EVGA's notify list for a 1300W PSU ever since. Can not run a 3rd GPU until I get one. 3080's are power hungry SOB's.

My old thread...
https://www.overclockers.com/forums...1-RTX-3080-and-GTX-1080-TI-PSU-recommendation

 

[Oldschool_OC]

Assuming the 8-pin wire is 16 gauge the following applies:
16 gauge wires can transfer a maximum of 3.7 amp (or 44.4 watts @ 12v) each. Multiply that by (8) and you get a theoretical maximum of about 355.2 watts per eight wires.
So even though the rail can produce more than 355 watts, you would need more than one set of eight wires to transfer more than 355 watts.
To be on the safe side I would say use at least eight 16 gauge wires per 300 watts.

However, if your 8 pin wires are only 18 gauge, the theoretical maximum power transfer drops to 220.8 watts per eight wires.
In this case, to be on the safe side I would say use at least eight 18 gauge wires per 150 watts.

*Edited to reflect the fact that I recently discovered the PCIe "spec" calls out 18 gauge wires.

 

[Blaylock]

I would run two separate cables to the 3080. As others have stated the max draw per 8-pin is 150W, however, there is also a max draw per cable and that is 288W from the PSU. Technically, it might work with a single cable, but it is out of spec and a fire hazard. I did a little research into your rig and it looks like your RM750x only has 2 PCIe and 2 EPS12v plugs. There are adapters out there to convert EPS12v plugs into PCIe, but your motherboard requires both.

I would upgrade to a larger PSU. I know it's not the answer you were hoping for but it's the safe choice. Running the 3080, even undervolted for mining, from a single cable is a fire hazard and you don't have other options with that PSU.

EDIT: I forgot to mention as a side note. You'll want to replace the thermal pads on that 3080 for mining. GDDR6x runs crazy warm. Many users are even mounting small heatsinks to their backplates to keep the 3080s and 3090s from throttling.

 

[EarthDog]

Sage advice.

Worth noting if you're considering the adapter route is your board only requires one 8-pin EPS connector. The second is optional.

 

[Oldschool_OC]

Not sure if anyone mentioned it, but there are also Dual 4 Pin Molex IDE to 8 Pin PCI Express adapters available for pretty cheap.

 

[Blaylock]

Yep. Just be careful with those. Max draw is 156W total per cable. Also, there are some really garbage Molex - 8pin adapters out there.

 

[Oldschool_OC]

Yep. Just be careful with those. Max draw is 156W total per cable. Also, there are some really garbage Molex - 8pin adapters out there.

Correct. 156W per cable is assuming the cable was built AT specification.

Having spent many years working in an electronics engineering lab, I can tell you from experience that there are those who build things BELOW spec, those who build AT spec and those who build ABOVE spec.

 

[Zerileous]

Late to the party but would add I know of one instance where a no-post situation was attributed to a daisy chained 8 pin cables on a Vega 64. Of of course maybe it was just a loose connector. In terms of the max wattage for a daisy chain cable, I would refer to the PSU manual, I know that Seasonic has one in their manuals.

An issue (or maybe non-issue) that I haven't seen mentioned is running an AMD and nVidia card in the same system. I'm not sure that this is possible in Win10, maybe if you used a separate OS to mine it could be made to work but at this point I'm speculating.

 

[EarthDog]

I think for mining (like F@H) you can mix and match.

 

[Blaylock]

You can mix in Windows 10 but for simplicity sake with the config file I ran 2 sessions of Phoenix miner, one for each. You just need to change the cdm port from default :3333(-cdmport xxxx) on the second session. Or disable remote control on the second session altogether (-cdm 0).