Voltage inverters, typically invert the current from direct current (dc) to an alternating current (ac) and transform or convert the voltage from 12 volts to 220-240 volts. Units are sold with a maximum wattage rating. Above this maximum wattage figure the inverters will cut out to protect themselves. For running lights, hairdryers and other appliances that do not have a heavy starting load buy an inverter that is a least slightly larger that your anticipated maximum needs (20%). For a microwave ignore the cooking power wattage stated on the front of the oven and check the wattage requirements on the data plate. It is likely to be in excess of 1.5 times the cooking power and again add 20%. For electric motors that have a heavy starting load you need to multiply the stated wattage on the data plate by 1.4 and more. See this blog article on voltage inverters for more information.
The most common uses for the voltage inverter is in cars, boats, camper vans, caravans, food trailers and numerous other uses. These modified sine wave inverters allow the alternating current to drop to zero as it passes from negative to positive and back again.