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Notebook and other small devices’ power supply efficiency

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
II 1W 39%
II 10W 64%
II 30W 75%
II >50W 82%
III 1W 49%
III 10W 70%
III 30W 80%
III >50W 84%
IV 1W 50%
IV 10W 71%
IV 30W 81%
IV >50W 85%
V 1W (>6V) 77%
V 10W (>6V) 74%
V 30W (>6V) 83%
V >50W (>6V) 87%

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.

6 Responses to “Notebook and other small devices’ power supply efficiency”

  1. Frank:

    Great article! It’s so reasonable to have an average minimum consumption labeled on passive power supplies – all power supplies should have this!

  2. Gustavo Penteado:

    Thanks for the article, but I still haven’t undertand at all.
    I have a DELL inpirion notebook, and i brought another power suplly directly from a dell call center.
    And arrived a “different” PSU (there wasn’t a dell logo and the connector wasn’t a octogonal shape as my original one).
    And analyzing the background the only thing I found different is this efficiency level (one is IV and other is V – the original).

    So I ask you, which one is better?

    – sorry about any writing mistakes, I’m from Brazil.

  3. William:

    Great post!

    For “V”/”10W”, could there be a typo? Instead of 64%, should it read 74%?

  4. Qian Qin:

    you’re right, it’s 74%

  5. Henry:

    Hallo Quian

    Habe mich auch gerade gefragt, was die Effizienzklasse V auf meinem Laptop soll, danke für die Aufklärung! Ich verstehe nicht so viel von Netzteilen, aber etwas von Solarstrom, der ohnehin DC daher kommt. PV Modul direkt an Laptop anschliessen, und noch effizienter Arbeiten? Meld dich mal, wenn dich das Thema interessiert.

    Gruss, Henry

  6. Matze:

    Ich habe grad das Netzteil meines Notebooks durchgelesen, weil es mal wieder soooooo heiß ist.
    Hat 65W und Efficiency Lv V also was solls^^ wird schon gut sein.
    Vielen dank für dein Artikel