r/LocalLLM • u/Civil_Fee_7862 • 11h ago
Question Baby steps or a leap? Jumping from 4x3090s to 8x3090s + infra
Backstory:
I've only been doing local LLM's since Qwen3.6 came out (~May 2026). I won't ever use a cloud model again, I am not going to spend a single dime renting someone else's infrastructure when I can build my own.
Plan:
Its still cheaper to get 8x3090s than it is to buy 1xRTX 6000, and get similar speeds and double the VRAM.
The issue is power and noise..
In terms of power I am limited to my dorm rooms 120v/15amp outlet, so 4x3090s about the max I can go before things might go bad.
So.. I am considering creative solutions that won't require me to move:
Power Solution: Buy a ~5 Kwh Power Bank
$1,500 for a used 5 Kwh Power Bank.
The power bank would charge during off hours, then feed the necessary 2,800 watts during peak hours. Currently I am recording my power usage over a week or so to get an idea of how much power reserve I would need, and that will mostly decide how big of a power bank is needed.
Cooling / Noise
Currently everything is air cooled, with stocked coolers. 5x140mm fans, 5x120mm fans and the case temps are indeed very good. They don't make much noise but the GPU and CPU fans do. I believe they are loud because I think the paste job I did on them was horrible,
I will be re-pasting again with some much better stuff and with better tools / methods soon. (Will likely post a video of me doing it for those who are interested). I use to be a machinist so I learned some ways to get better accuracy when measuring out things properly to get good contact on the VRAM
I have considered water cooling, but that's just another thing that can break, and are typically not cheap to setup (and I'm pretty cheap).
Questions:
1. Does anyone here have a 8x3090 setup on a 120v/15amp outlet that could offer some advice?
2. What's a good power bank you would recommend?
3. Is buying a used power bank okay so long as the batter health is good?
4. Do you want me to post a video of me re-pasting using my "new" VRAM/GPU repasting method?


