The device should tell you but you can always measure the current. A Thinkpad 600, for example, says it wants 16V at 2.6 amps. Volts X Amps = Watts, so the Thinkpad wants 41.6 watts. That probably covers charging the battery, so the normal draw would be less and you can tell with a multimeter. Given clouds and other inefficiencies, 40 watts is not a bad number to start with. If you want to run at night, you will need at least 80 watts of cells. Your battery capacity will have to be roughly 40 watts x 12 hours, 480 watt-hours. If you use a 12V car battery, your wires will need to handle about 3.5 amps. Somewhere, I have a book that has the relationship between wire gauge, resistance and power loss.
Compare what you need for an old laptop to a new 3.5 watt laptop. The 15 watt cell might give you better night run time and you might be able to use the built in battery instead of a 75lb lead monster. On Friday 12 September 2008, Brad Bendily wrote: > > So, i don't know much about calculating needed watts... how many watts > or amps would be needed to run a laptop and a cable modem? > Then we can figure out which charger we need... _______________________________________________ General mailing list [email protected] http://mail.brlug.net/mailman/listinfo/general_brlug.net
