Why microwaves in RVs can be temperamental
The microwave at start seems to be laboring, as is the generator, a Honda EU 2000i. It's my belief that starting all of the equipment is similar to starting an AC. Lots of things are requiring lots of power to get underway. After it's started, both the microwave and generator seem to calm down.
The following is from Wikipedia, and it explains my experience with my microwave and generator.
A microwave oven converts only part of its electrical input into microwave energy. A typical consumer microwave oven consumes 1100 W of electricity in producing 700 W of microwave power, an efficiency of 64%. The other 400 W are dissipated as heat, mostly in the magnetron tube. Additional power is used to operate the lamps, AC power transformer, magnetron cooling fan, food turntable motor and the control circuits. Such wasted heat, along with heat from the product being microwaved, is exhausted as warm air through cooling vents.
High heating power delivered directly to the meal, bypassing the kitchenware, makes microwave oven the most efficient appliance for cooking or reheating small meals.
A microwave oven consists of:
a high voltage power source, commonly a simple transformer or an electronic power converter, which passes energy to the magnetron
a high voltage capacitor connected to the magnetron, transformer and via a diode to the case.
a cavity magnetron, which converts high-voltage electric energy to microwave radiation
a magnetron control circuit (usually with a microcontroller)
a waveguide (to control the direction of the microwaves)
a cooking chamber