RM750 Fan randomly spinning for 15-20min

[Eazon]

Hello ! I have bought a RM750 brand new a couple months ago or so, and after noticing that the fan would randomly spin while in idle/browsing, despite pulling less than 100w (reminder, this 750w unit should only have its fan start spinning when around 300w (40%) of power draw)
Room temperature is always around 20°c or below,

After a few weeks communicating with the support, we finally settled on an RMA process, and i received the new unit yesterday, installed it this morning.

After about one hour of use, only browsing and watching youtube, i noticed the exact same behavior. The fan started audibly spinning for around 15-20 minutes before finally stopping again.

I don't really understand how this is possible. The replacement unit i received is apparently a refurbished unit, is it possible that it suffers the same defect, or is it actually how the psu should behave?

I still believe that the RMA was worth it, as the previous unit would not only have its fan spin but also emit a very annoying vibrating/humming noise, that doesnt seem to be present with the replacement unit.

But i have a hard time understanding why it is behaving that way.
And yes i am 100% certain it is coming from the PSU, i have made sure of it many times before even contacting the support. Feel free to ask what i did to make sure.

Has anyone experienced similar behavior and can tell me if its pretty normal? The support assured me that the fan should only start spinning at 300w+ load but i'm starting to wonder if its not just spinning after an hour or two to exhaust hot air buildup, in which case i feel marketing is just not fair.

Thanks in advance for your answers

[Mark_T]

Two thoughts come to mind, have you installed the PSU with the fan facing up or down?

If it is down then the fan will have to run more often as the passive mode will not have reduced natural convection to remove the heat.

Similarly the heat generated isn't all about the big loads, if you have a lot drawing on the 5V & 3.3V rails then that will disproportionately increase the heat generated.

Edited November 27, 2021 by Mark_T

[Mark_T]

40 minutes ago, Mark_T said:

If it is down then the fan will have to run more often as the passive mode will not have reduced natural convection to remove the heat.

Edit: "If it is down then the fan will have to run more often as the passive mode will have reduced natural convection to remove the heat."

[Eazon]

It is indeed facing down, as the corsair 4000d as an opening at the bottom, with a fan filter, while the top is a closed shroud

I do also have a couple SATA SSD (and 2 nvme ones aswell), a couple led strips (phanteks neon ones) and 6 argb 5v fans
Do you recon that could be the cause?

[Mark_T]

In combination, yes, it feels like that would be enough to cause the fan to run for a bit now and then.

In fairness to Corsair, the marketing says - "The RM Series' cooling fan doesn't spin until you need it, for near-silent operation at low and medium loads."

So I'd say they were covered.