I have in my server a Nexus NX-5000 R3 530W 82 Plus PSU. While measuring server's power consumpotion I noticed a peculiar thing. Even when I switch the PSU off it still draws 23W. Only by disconnecting the power cord did it go to 0W. I made the same test with my HTPC which has an Antec Neo HE 430W, but it behaved as supposed to, meaning that switching the PSU off brought the cnsumption to 0W. What might be going on?
I believe your motherboard is searching for a 'wake' signal. So just enough power is trickling through to detect a keystroke, network event, or USB signal. Most motherboards can even turn themselves on when their clock reaches a specified time.
Unfortunately the answer is not that simple. This is how it looks like:
- When the power cord is disconnected, the meter shows a consumption of 0W.
- When the power cord is connected, but the power switch of the PSU is set to 'off', the consumption is 23W
- When I switch the PSU on, the consumption goes to 39W, which I believe means that the PSU is powering the motherboard, which indeed has WOL enabled as well as RTC wakeup.
- When the systerm is running the consumption is 61W.
With my HTPC the picture is otherwise similar, but when its PSU is switched off, the meter shows 0W.
Edit: I switched the PSUs in the HTPC and the server. The result is the same, meaning that the PSU shich is now in the HTPC behaves exactly the same as when it was in the server, drawing 23W when switched off. I have been trying to test the meter with different appliances and I think it seems to be reliable enough.