Power measurement

AC line monitoring

Appliance level

This is a quick way to get a power reading at the wall outlet. There is a logging alternative to the Kill-a-watt. There is the Wattnode. Both of these are good options for monitoring at the wall outlet.At this point though, I want to be able to measure internal components too.

Internal measurements

• Measure power supply efficiency. (Compare at wall and at power supply outputs)
• Check effectiveness of cpufreq and powernowd.
• Compare power used by different hard drives and other components.
• Compare power use with and without WiFi board installed.
• Figure out how to power down unused components and see if it works.

Ideally I want to be able to measure power over long periods of time, so connecting my trusty Fluke 77 and watching the display is not an option.

Methods of current measurement

Series resistor - put a small resistance in series with the load and measure voltage drop across it. Simple, but wastes lots of power thereby defeating my whole purpose.

SCT - put a current clamp around the wire.

Hall-effect - put a hall effect device next to the wire. Allegro makes some specifically for monitoring current.

The SCT's that I happen to have are in the 100 AMP range, too big for this project. I either need smaller SCT's or a hall effect device.