When you run your generator, the converter/charger puts out 12 volts DC to operate the electronic controls on your microwave, etc., therefore the panel lights up. With genererator running, you should be able to operate your microwave and roof AC together on the 4000 watt AC power it feeds to the 110vac circuits. Start roof AC first, then microwave. Watch your after-market plug-in line voltage monitor/meter when running the generator or when plugged into shore power to make sure it stays in the green. Low voltage can damage AC and or microwave.