Measuring power consumption (was MP3 player)

[Bill Layer <blayer@uswest.net>]

The multimeter will do just fine but you will have to play one trick or 
another to make the necessary series connection with the power cord to 
measure current draw.. I have a special, short extension cord that has one 
conductor broken so that the meter may be inserted in series with the loop.

Set the meter for the current scale and measure the current draw with the 
device powered on. Then, keeping the device powered on, set the meter for 
an AC RMS voltage scale and measure the supply voltage at the wall - it's 
not wise to estimate, as AC mains voltages can be anywhere between 109 and 
126VAC - with 117 being nominal. Once you know current and RMS supply 
voltage, power (wattage) calculation is this easy:

P = E * I (Where P is power (in watts), E is energy (in volts) and I is 
current (in amperes))

I should mention that most all (even inexpensive) meters automatically give 
AC voltage readings in RMS - so don't get too concerned about this issue. 
If the meter doesn't say otherwise, it's giving the reading in RMS.