Well the thing to remember is that a car's 12V outlet is usually only guaranteed for a max of I think 10 amps, assuming there is nothing else loaded on the outlet. They may put in a 10 amp fuse in some vehicles. So you can't get more than 120W out of a normal outlet. This may or may not be enough power for what you want to do. Some vehicles use thicker wire and a much larger fuse.