this post was submitted on 22 Nov 2023
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Powering a GeForce RTX 3080 TI from an external power source (alien.top)
submitted 11 months ago by [email protected] to c/[email protected]
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I have a Dell R730 and a GeForce RTX 3080 TI GPU. I deployed these as a server for AI LLM testing and development. Due to the power requirements of the 3080 TI as well as logistics of power connector on the R730 mobo I was not able to power it from the motherboard of the R730. I purchased a Corsair RM850X and ran two 8-pin PCIe cables from inside the R730 out to the Corsair, which is outside the server. Since the RM850X is not connected to any motherboard it would not provide power even after I connected two 8-pin PCIe power connectors to the 3080 TI. I used a paperclip to short two pins on the 24-pin motherboard connector and it powered up the Corsair PSU and, consequently, the 3080 TI powered up and is now working. For the first time the R730 sees the GPU and I was able to install drivers and have seen HUGE performance improvements in the AI interactions.

I have seen posts and been told that this is not a good long-term plan and that there is even a danger in doing this. Given the constraints that I don't have another server or PC I can use for this project nor do I have an option to get another GPU that has less power requirements at this point I need to make this work with the hardware I have. So my question is--what are my options? This is working. I left it running over night and there have not been any signs of overheating or any other problems. That said, I don't want to play the fool and either ruin the GPU, the server, or both. How can I provide power to this GPU for the long-term in a way that is both safe and provides adequate power to it?

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[–] [email protected] 1 points 11 months ago

I'd recommend making a proper jumper for the 24 pin rather than using a paperclip.

[–] [email protected] 1 points 11 months ago

Google 'dual PSU adapter'.

There are two options:

1 - a 24 pin adapter that bridges the power-on pins to the other PSU

2 - a 24 pin adapter that takes a molex from the main PSU and uses a relay to power on the secondary PSU

Either works just fine.

[–] [email protected] 1 points 11 months ago

I found a bridge tool that serves as a permanent fix/replacement for the paperclip. Unless you all believe there is some danger in taking this approach of an external power supply that is not in any way connected to the motherboard but just provides power to the GPU, I think I'm good. This community is amazing. I am stunned at how fast you guys responded and got me squared away. Reddit rocks.

[–] [email protected] 1 points 11 months ago

Just a thought on electrical grounding issues - Any GRND imbalance between the external PSU and the server will result in a small current flowing through the card via the GRND traces. In a perfect world this should be negligible, however, to play it safe I would make sure the server and PSU are plugged into the same power strip at all times so they share the same ground bus bar. If you have a multimeter available I would also verify that the voltage difference between the grounds on the DC side of the 2 PSU's is exactly 0 is very very close to 0v.

[–] [email protected] 1 points 11 months ago

They used to make adapters that would go in-between the main power supply 24 pin and the motherboard, and hook to the 24pin connector of the secondary so it turns the secondary of and on with the primary. They were very useful for FX systems with multiple r9 290s. I would think you should still be able to buy them.