Question Corsair Case Fan RPM Drop

Nov 30, 2021
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In my current set up I’ve got 6 Corsair LL 120mm fans, 4 acting as normal case fans and 2 attached to the radiator.
My 4 case fans I keep around 1,600RPM but for some reason, one of the fans insists on running at 1,700RPM while the other 3 fans all run roughly the 1,580-1,600RPM.
However, when I get into any demanding game, the one faster fan that runs higher drops down to meet the others at 1,600RPM.


Anyone know what would cause this in the first place and why does gaming fix it? Why would gaming make the first fan behave like the others?

Set up: MSI Z690-A PRO running up to date Bios

All Fans have 4 pin connectors and are running at PWM. Tried DC, this phenomenon persisted.
 

Darkbreeze

Retired Mod
Try swapping that fan header with one of the other fans to see if the RPM difference follows the fan or stays with the same fan header.

Are all fans connected directly to fan headers, with no extension cables or fan hubs or splitters?
 
Nov 30, 2021
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Okay I will swap and report back my findings. Yes all 4 case fans are each connected to their own fan header on the motherboard.

I will see if the 100RPM discrepancy follows the fan or the header.

But what would cause heavy load/gaming to bring the one fan down to the other 3?
 

Darkbreeze

Retired Mod
Hard to say, but most likely I'd guess that it might simply be a manufacturing tolerance for that fan not as in spec as for the other fans, or could be anything really. Slightly out of spec RPM monitoring signal on the fan. Quirky PWM controller. Who knows. Longer trace to that fan header so a slight voltage drop on it compared to other headers. IDK. See if it follows the fan so we have an idea what system is at fault, if you really want to call a 100RPM discrepancy a "fault".
 
Nov 30, 2021
3
0
10
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Hard to say, but most likely I'd guess that it might simply be a manufacturing tolerance for that fan not as in spec as for the other fans, or could be anything really. Slightly out of spec RPM monitoring signal on the fan. Quirky PWM controller. Who knows. Longer trace to that fan header so a slight voltage drop on it compared to other headers. IDK. See if it follows the fan so we have an idea what system is at fault, if you really want to call a 100RPM discrepancy a "fault".
Did what you said. The discrepancy of 100RPM followed the fan, not the header. So it’s a fan with loose tolerances. I can live with that. But what makes it normalize with the other fans while gaming/during load?
 

Darkbreeze

Retired Mod
It's hard to say. I don't design fans or motherboards, so I really don't have an answer for that. Could be a slight loss of contact somewhere along the wiring or internal electronics and when temps rise just a little and voltage or length of pulse width increase, it's able to more accurately report it's RPM signal or something along those lines. I really honestly couldn't tell you exactly why but at least you know it's the fan now. Might also try leaving that fan connected and DISCONNECTING one of the other fans temporarily, just to see if, with one less fan running, that fan still does it as well. Probably will, but who know.
 

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