Power projector with car inverter
My advise would be not to use an inverter, but to use a direct 12V DC- 19V DC converter such as a &gt;70W (preferably a bit more) Laptop power supply for use in a car, which will almost certainly be able to output at 19V.
Your only concern is finding out if the laptop supply comes with the correct plug for your projector.
The advantage is that converting 12V to 19V directly is much more efficient than converting 12V to 110/240V and back to 19V again.
If you're using a car cigarette lighter type plug, please note that they're not really suitable for suppying large currents for longer periods of time. They can get very hot and even melt.
Your car's alternator should be able to deliver the more than 6A needed to keep the battery charged when the engine is running.