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I built a machine according to the specs of a computer magazine (c't, Germany). According to the magazine, the power consumption should be at around 10W.
I don't want to go into the specifics of the hardware but rather ask for general advice on where to look:
I updated the BIOS/UEFI version to the latest version, installed all the recommended drivers and unplugged all hardware that's not necessary to boot into Windows.
All that was left is the power supply, mainboard, cpu, cpu cooler and one SSD drive. But still I measured a power consumption of 50W, which is 40W more than it should be.

I tried booting Linux Mint from a USB stick, so I don't think it's some Windows-related problem..

Where else could I look?

Update 1

I dind't want the question to get closed for being too localized but if more details are necessary, here they are: The system is a desktop PC. The power consumption is measured using a Brennenstuhl PM 231 device, which was tested also by c't and they found it quite accurate.

The PSU is an Enermax ETL300AWT, the mainboard Intel DH87RL (Socket 1150) and the CPU Intel G3220 (Haswell).

Update 2

There is no online version of the article*. The most details I found can be read on its project page (in German, though...)

(*)You can pay for downloadable PDFs, however.

English translation of that project page

Update 3

Regarding the sceptics: It may sound ridiculous but apparently 10W idle consumption is possible with Intel's Haswell architecture. As a kind of proof, there's an additional Blog article explicitly listing the steps needed to reduce the idle consumption to 10W.

Additional hardware: I measured the consumption without the HDD, and as expected the usage dropped by around 10W. I have no chassis fans and the CPU fan is a "Scythe Mugen 4" model. It runs at around 600rpm so I think it won't draw much.

When stripping off all my extra components I should be at 10W. But I'm not getting anywhere near that. I would be happy to see "just" 15W in the stripped down version but currently I'm not getting below 50W no matter which component I remove. As I see it this cannot be explained by the PSU being less efficient at lower consumption.
I also waited half an hour or so (also checked that no Windows updates were running in the background) and the consumption dind't drop by more than a few watts.

  • Without specifics we can't figure out what is your problem and without the article (is there an online version?) we can't figure out if their readout is any good. Still, 10W for a laptop seems very very low. – Doktoro Reichard Nov 9 '13 at 18:23
  • How large is the PSU? Your PC is probably at the minimum power draw where the PSU is inefficient (i.e. you cannot use a 500W power supply if you expect to consume only 10W). "I don't want to go into the specifics of the hardware" -- You're asking a HW question without providing any details. superuser.com/questions/446419/… – sawdust Nov 9 '13 at 19:25
  • Did you set up the BIOS as described in the "Einstellungen für das BIOS-Setup" section on the project page you linked to? Also, make sure it isn't doing anything much when you measure the power consumption. – Andrew Morton Nov 9 '13 at 19:43
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    "power consumption should be at around 10W" -- That's a ridiculously low number for a PC. Is this actual power consumed (net from the PSU) or measured at the wall outlet? This test of your PSU indicates that the PSU is reduced to 75% efficiency at 22W load, so if your PC actually required only 22Watts, then you would still measure 30W at the outlet. If you manage to reduce the PC power requirements more, then the PSU's efficiency will go down even further, so there will be only minor power savings. – sawdust Nov 9 '13 at 19:49
  • Your question is interesting, but I vote to close it. Building a ultra-low-power desktop PC is not common knowledge (e.g. besides using Intel Atom and picoPSU), and you have followed a "secret recipe". We don't know what is in that "secret recipe", so we can only guess at how or where your build went wrong and fails to live up to expectations. Also note that that Enermax reports that the PSU is 2% more efficient on 230VAC than 115VAC. – sawdust Nov 9 '13 at 22:34
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Lets start by listing some of the components you are using:

  • Motherboard and chipset (which can use a lot of power)
  • CPU
  • CPU fan (not much, but if you aim at 10 Watt then the CPU fan will show up)
  • Case fans (2-5 Watt each)
  • RAM (2-3 Watt per DIMM)
  • PSU

The Motherboard looks like a regular desktop motherboard. The H87 chipset alone can draw up to 4.1 Watt. That is almost half your desired usage.

The CPU uses up to 35 Watt. It will not use it at idle, but I doubt it drops belows 3-5 Watt even in C6 state. It is a 22nm chip which uses little power under load, but there is always some current leaking and the smaller the architecture the larger the influence of this is. (This chip is build on 22nm, which is small.)

The CPU fan. I doubt it draws much. I measured the power usage of larger regular desktop fans and those used 3-5 Watt. Which means the smaller and less power using CPU fan usually gets ignored. But if you aim at 10 Watts then you take this into account.

Optional case fans. I got 6 of these. unplugging 4 of these drops my power usage by 20 Watt, so I am going to estimate 5 Watt per 10cm-ish fan.

RAM. I measured an increase of 2-3 Watt per DDR3-1333 DIMMs @ 1.5 volt. Scale accordingly to the memory you used.

PSU: A PSU often yields good results between 20% and 80% of its maximum rated power. Beyond that zone efficiency rapidly drops. The PSU you used is rated at up to 300 Watt and should be used in a system drawing less than 60 Watt. If you draw less it will not reach its stated 88% efficiency. Instead it might draw twice the power at the socket as it is providing to the components in your system.

[Edit] Ok, that was a little pessimistic. According to Hardwareinfo your PSU seems to be 74.8% efficient at a load of 22.5 Watt.

In other word, when supplying 22.5 Watt to the system it is drawing 30.1 Watt from the wall socket. And if you measure 50 Watt at the wall then it is supplying about 42 Watt to the system. (At that load it is already up to 84% efficiency).

Edit2: Obviously I can not link to an article you have to pay for, but this image seem to be free. It shows a clasical HDD and a SSD. The SSD would draw between 2 and 5 watt, depending per model. A Rotating drive often idles around 10 Watt. I assume that they used a drive which spun down on idle, so you would need to wait for that to reach the 10 Watt of send it a direct command. (E.g. using hdparm -S).

enter image description here

  • Thanks for the detailed answer. I updated my question accordingly with respect to the possible issues you mentioned. – foraidt Nov 9 '13 at 21:10
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The low-power consumption of this project PC seems to require meticulous adherence to:

  • HW components,
  • BIOS setting and
  • Windows drivers (i.e. you may not be able achieve this with Linux).

The user forum does have a thread about

The Energy Saving PC consumes too much

I have the PC-building project from c't 19/13. However, my DIY never consumes less than 15 watts at idle. You have, however, promised only 10.3 watts. What am I doing wrong?"*

The project authors admit that, after following their own instruction again, they got similar results of 15W power consumption. They traced the problem to the installation of the MS Windows driver for the SATA AHCI controller. The project requires the installation of the Intel Rapid Storage Technology (RST) driver. Failure to install the Intel driver would prevent the CPU to go into deep sleep mode.

  • I'm aware of this problem and its solution. That's what I meant with "installed all the recommended drivers". But I wouldn't even complain about 5W... – foraidt Nov 9 '13 at 21:09
  • Try installing some SW tool that will indicate if the CPU ever goes into low-power modes like deep sleep mode. Maybe CrystalCPUID? – sawdust Nov 9 '13 at 21:16
  • I couldn't get anything useful out of CrystalCPUID. It seems it doesn't support the CPU. However, in Windows Task Manager I can see that the CPU frequency goes down to about 0,78GHz when the machine is idle. – foraidt Nov 10 '13 at 9:35

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