Saving Power at Home & Work

Laptop Computer & ADSL Modem


The graph above shows the way a laptop computer used together with an ADSL modem uses electricity. The laptop is a relatively old Fujitsu Siemens Amilo (Centrino processor) and the modem is the Telkom Marconi WiFi ADSL modem. The test started with both devices running with no activity (ie simply switched on but doing nothing for about 20 minutes). The laptop was then unplugged from its powersupply and used independantly for about 25 minutes, during which time the data logger recoded the power drawn by the ADSL modem alone. After that, the laptop was plugged back into its power supply and some work done (including some spreadsheet calculations, some document typing and intermittent browsing of the internet) for a number of hours. You can see a number of key characteristics:

The system is a completely resistive load, meaning that current and voltage are completely in phase and thus Watts consumed are almost exactly the same as the Volt-Amps (VA) consumed.
The Laptop and ADSL modem, both in inactive mode, used 20W combined. The ADSL modem used 10W in inactive mode .
After the laptop was reconnected to its power supply the peak power comsumed was due to the battery drawing relatively large amounts of power as it recharged.
Once the battery was recharged, the laptop and modem used between 25-30W combined, in normal use.

The summary figures for the test are:

Max. Power drawn 50W
“No Activity” Power drawn (laptop & ADSL modem) 20W
“No Activity” Power drawn (ADSL modem only) 10W
Normal Use Power drawn (laptop & ADSL modem) 25-30W
Total energy consumed during test 0.08kWh
Engery consumed per hour of normal use 0.03kWh

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