12/240V

The rule is simple. To allow for the power losses in the inverter you divide the power by 10 and that will give you the answer in most cases. If you purchase a 12 V power supply for your computer it will be more efficient and could cost you less. In that case you divide your power input by 12 (as you can see a 12 V PSU will drain your batteries less.)

PeterD

90W for the laptop plus about 10% inefficiency if you use a 12v converter direct to the laptops voltage.

Ie 100W.

P=VxI or I=P/V

The current is then 100 divided by the voltage, lets say 13V
=7.8A.

If you use a 240V converter and the laptop power supply you have another 10% inefficiency. That would make it about 8.9A.

What make is the laptop.
I run a Compaq Presario on a 6000ma Projecta converter no trouble at all
Runs at 19volts all day. This way is alot less messy that having extra wires to an inverter and then to the stepdown to the laptop.

Why not just buy the proper 12 volt adapter to run it?.

We use a little Tragus switchmode one ....about 70mm long, 40mm across and 10mm thick.

Hi all, thanks for your replies.
Rainer