I have a Toshiba laptop which I use on board my boat. The boat has two 85 AH batteries. What would be the power consumption of my laptop?
Jim Sexton responds:
Assuming that your two 85 AH batteries are fully charged, connected in parallel, and that youre running your Toshiba through the cigarette lighter adapter with 100 percent efficiency, you could expect your computer to run for about 56 hours (three amps into 170 AH) before your batteries go dead. This also assumes that you are not running anything else off the batteries like your GPS, radio, running lights, etc., and that your Toshiba can operate at 12 volts (it's rated at 15 volts) without tripping the internal reset due to low voltage. The only way to know this is to try it out or contact Toshiba, if you can't find any information on low-voltage operation in the user's manual.
Realistically, you should use the inverter because it operates at close to 90 percent efficiency and uses less than two amps of power. In this case you could expect your computer to operate for a maximum of 30 hours (five amps into 170 AH times 90 percent) before the batteries go dead. Again, I'm assuming that you have only the computer and inverter hooked up to the batteries. If you are using anything else, you need to determine its amperage and add that total to the five amps for the computer and the inverter, then divide that into 170 and multiply by 80 percent. (Other electrical/electronic units are not as efficient.) Of course, after the ship's batteries go dead, you can expect another two to three hours from the computer's internal battery. I would also recommend that you connect a voltmeter to your ship's batteries and keep an eye on it when you are using the computer or any other electronics solely on the batteries.