Power Usage

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Measured power usage

Measured with Kill-A-Watt, 119V input, tested with 720p output to LCD (not plugged in to wattmeter)
Note: These figures have also been confirmed with a 240V unit.

  • Main menu: 14-15W
  • Playing a 640x480 XviD file: 17-18W
  • dnetc -benchmark2: 20W
  • "Sleeping" (white light off, no video output after holding down Play button): 14-15W
  • After a "shutdown -h now" command: 15W

Questions

  • Is there any way to further reduce power usage, e.g., disabling the graphics processor?
  • Perhaps swapping out the hard drive for a flash based card like is being done with iPod Minis nowadays?
  • What about a "Shutdown" frappliance that physically turned it off. (Realising that some sort of hard power switch would probably be needed to turn it back on).

Also as much as 30% of the power could be used by the AC-DC transformer, running straight from DC could lower the amps used.

  • Doing a pmset -g yields:
-bash-2.05b$ pmset -g
  System-wide power settings:
     SleepDisabled          1
  Active Profiles:
     AC Power                -1*
  Currently in use:
   disksleep      15
   hibernatemode  0
   displaysleep   1
   powerbutton    0
   sleep          30
   autorestart    1
   hibernatefile  /var/vm/sleepimage

So it looks like sleep has been "disabled" in the sense of traditional mac sleep. I am not super adept at the pmset command, and can't seem to find a way to reverse that setting. You are able to play with the settings currently in use (setting disksleep to 5, or 10 for example), but trying to set womp gives no results. A pmset -g cap gievs you:

-bash-2.05b$ pmset -g cap

  Capabilities for AC Power:
    displaysleep
    disksleep
    sleep
    autorestart
    powerbutton

Measurement Requests

  • Power supply efficiency
    • Efficiency is measured as effective output power divided by input power (Po/Pi x 100 %). Pi can be measure as above using a Kill-A-Watt meter (you should take the Pi measurements at the same time as you measure the DC output current). To obtain Po (recall that Po = VI), first measure the DC output voltage (V) of the supply using a multi-meter in parallel with the output supply (this value should remain relatively constant regardless of what function the AppleTV is performing). Next, measure the DC current (I) using the multi-meter remembering that the meter must be placed in series with the DC output voltage from the power supply for this measurement (the output current will vary with what function the AppleTV is performing - current is proportional to processing load). Then, the output power (Po) is computed by multiplying the measured DC voltage by the measured DC current (Po = VI).