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Asus ROG Thor 850W - Swap Original Fan with Noctua

Level 9
The problem with ROG Thor 850W PSU is its fan noise. One week after i bought the PSU, the noise started. A very annoying bearing / motor noise when the 0-rpm is disabled, or when the load is high enough for the fans to start. The noise of the PSU is literally the only noise i can hear in my system right now... Dealing with RMA is not an option, especially during the covid period, as it's going to take too long and i already know it's going to be rejected anyway, with the typical response "it sounds as it should sound". No Asus, when you build a premium silent system and you pay that much money for a PSU it does NOT sound as it should.

So, i've decided to not give a damn about the warranty and swap that cheapo fan anyway, with a quality one that will endure, making sure it meets the specs.

I've found the specification for the original fan (Model: PLA13525B12M - shown in the screenshot below (curve 2) ).



1. I know i will void the warranty.
2. Yes it can be dangerous, but i can handle that kind of stuff and always take precautions.
3. There will be some cable soldering with thermal heat shrinks, for the 3pin to 2-pin convertion.
4. New holes need to be drilled on the fan, to match the 135mm metal bracket that holds the fan.


The best candidate for replacement in my opinion, is the Noctua NF-A14 IndustrialPPC 2000 (3-pin). It's 12V, meets the curve of the original fan, and has pretty much the same airflow and better static pressure. Its minimum voltage seems to be 4.95V and it's running stable at 5V. I shouldn't have any problems at 5V and runs quieter at low rpm.

My concern however is the starting voltage of the PSU for the fan. Most PSUs start with a higher voltage (say 7V), and after 1-2 sec drop it to 5V where it stabilizes, until higher rpm and thus voltage is needed. Some people have tried other fans on other PSUs, like the Noctua NF-A14 FLX, which have a minimum voltage of 5.5 - 6.0 V. As a result the fans would not keep spinning with a PSU voltage of 5V. That makes sense.

There are PSUs however that drop the voltage below 5V, and that would cause a problem.
Does anyone know what the PSU minimum voltage for the fan is ? Does it stabilize at 5V or drops lower ?