Green IT is a big topic, that’s why more and more computer power supplies get a 80 PLUS label for showing off their superior efficiency. But if you every decide to run a Intel Atom based PC, use a PicoPSU, just power your notebook or charge your phone, you won’t really find out how efficient the power supply is. I came across this problem while searching for an efficient power supply for my new Atom-based home server. First, I wanted to use an 80 PLUS 350W power supply, but after reading some reviews, I found out that they are totally inefficient (<50%) on low load (<50W), which the targeted power consumption of my new home server is supposed to be. So I googled and found the PicoPSU, advertising >93% efficiency. Wow great, but wait, it needs to be powered by 12V DC. How efficient is the converter from 110/220V AC to 12V DC? No word on the manufacture site. I tried to google for efficient converter, but had no luck, so I gave up… until the case of my new home server arrived, a Gigabyte MIB T5140.
The Gigabyte MIB T5140 comes with a passive power supply which converts from 110/220V AC to 12V DC and has a labeled efficiency level of “V”. What the hell is that supposed to mean? Is that good or bad? I started to look at my other passive power supplies and found another label on the Toshiba R400′s. This time, it says “IV”. I guess they are meant to represent numbers, 4 and 5. But is higher better? I started searching again until I found the be-quiet notebook power, which has a “CEC” efficiency of “V”. That was the missing clue. CEC stands for Canadian Energy Commision (Energy Star) and would be perfect for certifying power supply efficiencies. But how efficient is level “V”? I started going through white papers of CEC and they only mentioned what I-IV mean, showing that V is reserved for future use. How can I have a level V power supply then?
I started to dig deeper and finally found a paper about International Efficiency Marketing Protocol, which finally revealed what efficiency a power supply has to have at what level including level V. And here are the results. I created a little table to show you how the the levels correspond to the actual efficiency.
|Level||Max. Output||Min. average efficiency|
|I||-||lower than all other classes|
So when you look at those values, you can see that III and IV are pretty much the same, only level V shows real improvement. At the same time, when you think that you are using a PicoPSU with 96% efficiency, you would actually only get 87%*96%=83% total efficiency, which isn’t so great at all.