Power Consumption

| experiment | measurements | power | watt

I have mentioned many times that I would like to know how much current something is drawing, so today Nic brought me a mains power meter. It is a very simple meter which plugs between the mains and the device and can measure volts, amps, watts, frequency, and a few other metrics. I decided to run around my house measuring everything I could.

Methodology

A couple notes about my methodology, firstly, I was very lazy in my measurement taking. I repeated some of the measurements, but not all. However, when I did repeat the measurements they always seem to have the same value, so this discouraged me from repeating.

To test a device I would plug the meter between it and the mains electricity and give it a some time to settle. Once settled I would take the reading. Sometimes the reading would flicker between two values, in these cases I took the higher of the two. Finally, I noticed that after I turned the devices off the meter would always read 8W. Either the meter was unable to read less than 8W, or zero was not calibrated correctly on the meter.

All these measurements were taken in my house in the UK, which according to my meter has mains electricity at 248V and at a AC frequency of 59.9Hz

Results

Device (status) Power Usage (watts)
xTune Speakers (standby) 24W
xTune Speakers (on no music) 25W
xTune Speakers (on vol30) 25W
xTune Speakers (on vol60) 50W
 
TFT Monitor 15″ (standby) 11W
TFT Monitor 15″ (on) 27W
 
TFT Monitor 17″ (standby) 9W
TFT Monitor 17″ (on) 38W
 
Nic’s laptop (web browsing) 35W
Nic’s laptop (playing game) 59W
 
xbox 360 (standby) 10W
xbox 360 (dashboard) 150W
xbox 360 (game) 158W
 
Sky+ Box (standby) 20W
Sky+ Box (on) 29W
 
Wii (standby – red light) 9W
Wii (on) 24W
 
TV (standby) 9W
TV (on) 95W
 
Kettle 2300W
 
My PC (off) 10W
My PC (booting during POST) 230W
My PC (booting) 130W
My PC (idle – Windows) 128W
My PC (game) 154W
My PC (1 core prime #) 142W
My PC (2 core prime #) 152W
My PC (3 core prime #) 160W
My PC (4 core prime #) 163W
My PC (sleep) 13W
My PC (idle – Linux) 150W

Some observations I made about these results:

  • My speakers use the same amount of power playing music as when they aren’t. I assume this is because the amps in them are always trying to amplify the signal.
  • My Sky+ box is pretty poor at conserving power. I found this interesting because Sky made a big deal about the Sky box automatically turning off at night. It even advertises this fact in big letters on the side of the packaging.
  • My PC which has a 800W power supply, with a quad core Intel, 4GB of RAM, and 6 harddrives, obviously doesn’t need 800W of power. The peak value, which I found during POST, was only 230W, with it idling (in Windows) at 128W.
  • Linux uses more power than Windows! This is using the latest Debian testing (2.6.30-8), and Windows Server 2008. Clearly, Linux has less energy efficient drivers, or is not powering something down that Windows is.
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