Avian’s Blog

Some time ago I attempted to measure the power consumption of my Eee PC with different settings for CPU clock and peripherals and confirm some findings on the Eee User forums.

On the second try I managed to get some results. First the measuring setup:

Eee is obviously very sensitive to voltage swings and I only got it more or less stable after I tried this with a second multimeter (with the first one Eee would not even boot). Soldering the biggest capacitor I could find in the workshop directly to the power connector and shortening the wires as much as possible also helped a bit. Even so turning on the camera repeatedly crashed the machine, so I couldn't measure its effect on the current.

Results (CPU clock as reported by cpufreq-stat):

All peripherals off, CPU idle:

• CPU clock at 113 MHz: 1.06A
• CPU clock at 900 MHz: 1.06A

All peripherals off, CPU busy:

• CPU clock at 113 MHz: 1.12A
• CPU clock at 900 MHz: 1.22A

Wireless LAN on, idle, CPU idle:

• CPU clock at 900 MHz: 1.17A

Card reader on, idle, CPU idle:

• CPU clock at 900 MHz: 1.14A

This confirms what other people have found out. CPU throttling is basically useless in Eee: There is less than 10% difference in current draw at full load and no difference in idle.

I also expected larger savings when you turn off the peripherals. Each thing you turn on but don't use costs you around 100mA, which is not that much. It would be interesting to also see how much difference you can make with backlight settings.

The computer was still crashing every few minutes so I think I satisfied my curiosity (and pushed my luck far enough) for now.