Ran inverter but keeps tripping breaker.

How many watts is the microwave?

If it is say 1500, then you need to add the startup current into the equation to the wattage of the inverter.

Also thinking about it, I've got an inverter that I bought a while back that says on it 2000 watts but when I looke at it after I installed it, it said 2000 watts peak and 1100 watts constant power.

 

You are overloading it. Micro waves take A LOT of power shut off everything else before you use it. You need to look at getting a 700 watt micro wave. Like Ridgeline said the inverter is probably 2000 peak do some reading and math on both mirco wave and inverter or you will kill your battery's. The fridge is eating up a lot power already and you are more then likely using a power strip which is a no no.

 

The microwave maybe 750 running, but what is the surge value? It may spike at 1200. The surge is alot higher when it first turns on. Todays inverters are not 2kw all the time. I would not be surprised if you find you actually have a 1.5kw with a 2kw surge. You may need to get a second one of those inverters just to run the microwave. Otherwise you will probably need to get a 2.5kw inverter (2500 watt peak, 2250 load).

 

How many amps is the breaker rated?
If you keep tripping it it will get weak and will handle less amperage over time.

 

You sure it's 100 amps? That should not trip with a inverter.