Hey guys, I have Corsair RM550x that is turning on/off its fan in 65-70 min cycles when PC is on idle. When PSU fan is off I meassure 31W from wall and 21W when fan is off. Other PSUs are not like that and they are around 25W. Funny thing is that fan shouldnt even spin below 220W iirc and I found it hillarius that its using less power when fan is on. PC is working fine, but is this normal?
Edit: specs - MSI Z270-A PRO, intel G3930, 8gb ram, 2 sata SSD and no GPU
Edit 2:
Thank you all for helping me out!
I believe that no flow in case caused PSU overheating and due to lower efficiency at higher temp PSU was using more power. Enabling case fans with small positive pressure fixed the problem immediately and now its stable at 24W on idle. On the next diagram PC was idle for only short period of time, so you can also see power curve when it was running some services, but still "much" less than 30 W.
Edit 3: Before this post I asked Corsair about that, but got only bot level responses. Conversation was going in circle and then I gave up :D
OP, couple things:
The trigger for that fan on signal is going to be heat, not wattage. Granted those things usually go hand in hand but there are a handful of reasons that could be responsible for the behavior you're seeing:
Your PC is exhibiting an unusually high draw on one depreciated rail and pushing that part of the PSU near it's limit. Legacy components can be good for this, -12V is a great example of a depreciated power supply voltage.
You're seeing heat from something else soaking into the PSU. GPU is a good internal example. If you're an audiophile, headphone amp is a good external one especially if it's sitting on the tower.
PSUs are designed to allow other case ventilation to pass through them for cooling. You've probably got another non-PSU cooling issue - clogged filter, dead or dying fan, negative pressure.
Lastly, it's hard for us to say whether that power draw is appropriate without knowing more about your PC. In general, for a desktop with a dedicated GPU it's in the ballpark but again hard to nail down specifics. It's a big ballpark. Things like what idle states are supported and enabled can easily account for 5W.
Yeah sorry , its MSI Z270-A PRO, intel G3930, 8gb ram, 2 sata SSD and no GPU. Ill add that to main post. Thanks for input mate, its bit more clear already, but still weird tbh. All that could explain fan behaviour, but why is it using less power when fan starts.
Its true, my case fans are off since Ive set them to start spinning when CPU reach 45C and that is almost never. I guess Its not good to have 0 air flow. I should change case fan curves and see
MOSFETs are less efficient outside their thermal envelope. At the micro-scale you're talking about, you could be chasing loss of efficiency due to heat.
Your tips led me to a solution, but some statements in other posts are also correct.
I believe that no flow in case caused PSU overheating and due to lower efficiency at higher temp PSU was using more power. Enabling case fans with small positive pressure fixed the problem immediately and now its stable at 24W on idle. On the next diagram PC was idle for only short period of time, so you can also see power curve when it was running some services, but still "much" less than 30 W.
Thank you a lot and have a nice day !!!