Many thanks. i want to use my arduino mega directly in my car. I used there an adapter from 12v to 5v because i use an nextion lcd too and mega don;t have enought power to supply the nextion. if i power the arduino directly with 12v from car wire it will be too hot, I think 12v is too much for mega. other thing is i want to put mega in a place where i have hard access to it and if i want to modify something i must put the usb cable inside.