External power supply for additional GPU?

[Micha]

Hi,

I use some of my cards per PCIe extension cable outside my PC and I think about to add a 3090ti to my system (2x2080ti, 1080ti) per extension cable too. But my current power supply is good for 1200W only. I ask me, if I add the 3090ti than could I simple use a second power supply for the 3090ti? Or will two power supplies create dangerous difference voltages and destroy my system?

-Micha

[Yard2380]

I would advice against this, I have been looking into similar solutions and bought (but never dared to use) a small piece of hardware that would direct the power up signal to the second power supply. (So that they at least shutdown and start together) I feel it would be better to go with a 1600 watt power supply, drop the 1080ti (still good to sell) and stick with the 3090 and the dual 2080ti's. The 1080ti has no raytrace support and I guess it would be your viewport card. I use 3x 1080ti at the moment and render on all 3 cards while doing a lot of other *light tasks, the lag from 2 years ago is gone, drivers are better and I can still enjoy youtube and netflix while all 3 cards are on 100%. I would not trust a machine with dual PSU. Another option: throw all cards in, check what their max wattage is and undervolt them to keep them within the watt limits of the psu. This will reduce the performance with a small margin. (So render times will go slightly up... keep that Raytrace stuff in mind as well...) This can be done in software and requires no mechanical tinkering. With a 1600 watt supply you can probably power all 4 cards without issue. Unless the rest of the system is power hungry too. (couple of mechanical drives, AMD cpu etc.) Also keep in mind your pci lanes, with 4 cards you might run into small bottlenecks if you also do a lot of writing to disks. This is a serious incoherent piece of writing, so let me know if this makes any sense at all.

[Muhammed_Hamed]

2 power supplies are totally fine. Get this cable,
https://www.amazon.com/Female-Power-.../dp/B07DCNHPZ3
And you are all set, I have used this for years.. it is quite popular in mining or multi-GPU setups (there are many cases that support dual power supplies)
Even without this cable, could use a paper clip to run the second power supply ..

And yeah drop the 1080ti, and stick to RTX rendering.. and don't worry about PCIe bandwidth with 3 or 4 GPUs, your Threadripper is more than capable of handling that

[Micha]

Great suggestions, thank you very much.

Sidenote: my experiences are not so good with RTX yet, often, if I compare RTX vs. Cuda the RTX mode is slower. But I suppose so it will be improved over the time and better in the future.

[Micha]

An other idea, maybe Muhammed_Hamed you know a solution for this need too.

I checked the power usage of my current setup and in hybrid mode, if all GPU and CPU are running, than I need 760W. I have a 1200W power supply and I suppose so it could be enough for an additional 3090ti (350..400W). My problem is my power supply provide 12 x 8(6)pin connectors and the 2080ti need 3 connectors - 2x8+1x6. Is there a way to split a cable so that two connectors are enough for the 2080ti? I think the power supply provide enough power per two connectors to drive a GeForce RTX 2080 Ti GAMING X TRIO. I have seen there are adapters ... could this work?

[francomanko]

do you have a mount for your external gpu? Or is it in a case?

[Micha]

I have no mount for the external GPU. It's laying beside the PC.

[Muhammed_Hamed]

I have seen there are adapters ... could this work?

Don't do that, you cannot use a splitter on a single 8-pin with any of these cards.. it is gonna crash on heavy load

my experiences are not so good with RTX yet, often, if I compare RTX vs. Cuda the RTX mode is slower.my experiences are not so good with RTX yet, often, if I compare RTX vs. Cuda the RTX mode is slower.

This happens if you mix between the cards, it is not really recommended (the 1080ti will slow everythinig down) or if there is other issues, you probably need to figure this out
RTX has been always faster for me on 2xxx and 3xxx .. on some scenes more than others, but most importantly it is not slower

[piotrus3333]

8 pin is 150W max.
and do not get rid of 1080 - still more than enough to run displays.

[Micha]

Don't do that, you cannot use a splitter on a single 8-pin with any of these cards.. it is gonna crash on heavy load

My plan wasn't to use one 8-pin connector. The 2080ti is using less than 300W, but the MSI TRI Gaming has 3 connectors. My idea was to use two 8-pin connectors (300W), but split one of them for the third needed 6-pin connector. All together the not overclocked 2080ti could use until 300W.

[piotrus3333]

pci express by itself is 75W i think.

[Micha]

Sounds good, so two 8-pin connector + PCIe would be 375W. More than enough for the 2080ti.

I got an idea, checked the power usage per CPU-Z and found my 2080ti needs max. ~200W and the 1080ti ~180W. This match to the measured power usage of the whole PC of 760W.

I will try the power splitter adapter. Looks like 1200W could be enough for four cards. I'm curious.

[Micha]

2 power supplies are totally fine. Get this cable,
...

Hi Muhammed_Hamed

the next hardware upgrade is imminent and now it's really no longer possible with one power supply. If I switch off the external power supply for the external GPU, will the unused GPUs interfere with the others?

Can I simply switch the external GPU on and off at any time or is a restart necessary?

[JezUK]

2 power supplies are totally fine. Get this cable,
https://www.amazon.com/Female-Power-.../dp/B07DCNHPZ3
And you are all set, I have used this for years.. it is quite popular in mining or multi-GPU setups (there are many cases that support dual power supplies)
Even without this cable, could use a paper clip to run the second power supply ..

And yeah drop the 1080ti, and stick to RTX rendering.. and don't worry about PCIe bandwidth with 3 or 4 GPUs, your Threadripper is more than capable of handling that

Muhammed_Hamed ,

Thank you for that cable recommendation, do you also have recommendations for Riser Cables for the GPUs as well please?

Many thanks

[Muhammed_Hamed]

If I switch off the external power supply for the external GPU, will the unused GPUs interfere with the others?

Hi Micha,

There shouldn't be an issue with this setup

Can I simply switch the external GPU on and off at any time or is a restart necessary?

Best is to do this when the machine is powered off

Best,
Muhammed