I noticed something funny with my new Enermax Modu82+ 625 PSU in my P180 case. Even though the Enermax plot of fan speed shows the PSU fan to stay at 450rpm up to >300W DC, at 260W DC mine is at 820rpm. However, it only does this when mounted in the case, not when running on the desktop. Removing the case door drops the rpms somewhat down to 730rpm, but far higher than when it's out in the open. My suspicion is that this is because the airflow is impeded by the narrow space right above the psu fan that the air has to pass through, as the cross section of that section is way smaller than that of the fan itself. (If it was flow impedance from drawing air past the hard drives and the front grille, it should not be a factor after removing the case door, one would think.)
Does anyone have ideas about how to fix this? It's nice that the psu is mounted in the middle of the bay so it can be mounted both ways, but it does split the available air channel in two. If the PSU was mounted flush with the case floor, there would be more space for air flow above, but that would require removing the platform and cutting a new hole in the back.
Thoughts? It's not like it's super important, because the Modu82+ is quiet enough even at 800rpm since when the machine is at full load, other fans (notably the 250mm fan to the external water cooling radiator) speed up too, but it offends my sense of perfection...
cheers,
/Patrik