I'd dare say it's a rating thing.
I'd wager the 800W is the power the magnetron puts out into the cooking area.
NOT the power it draws from the wall.
Now I have no idea how efficient a magnetron is, but if it's less than 50%, you're asking 1600W out of a (probably overrated) 2000W Inverter.
OK, scratch that, I just googled:
The modern magnetron is a fairly efficient device. In a microwave oven, for instance, a 1.1-kilowatt input will generally create about 700 watts of microwave power, an efficiency of around 65%. (The high-voltage and the properties of the cathode determine the power of a magnetron.)
Lets assume this is NOT a brand new microwave.
Lets assume even if it is, it's not usually a luxury product that many people spend a Grand on, so the Magnetron is PROBABLY cheap, regardless.
So my 50% efficiency is probably about right; possibly even less.
I'm also not sure how Magnetrons react to Square wave power, as compared to Sine Wave power.
Is it a Sine Wave inverter?
It's a power thing.
The reality is that most inverters, regardless of brand, in the 'same size package' really hate giving more than 1500W from a 14V source (Roughly 10A), they're just built to a price point, and the thickness of an average circuit board trace starts to be a limit from heat.
If you really want to use a microwave on the road, hit up Kmart or Target.
First, of all, they have a brand new 700W for under $50.
So instantly, it's a little less power, and MIGHT just get through (hopefully its magnetron is newer also).
If that doesn't work, those new ones are digital, and have power levels!
You should be able to make it a 500w microwave or less by turning it down on the menu.
Edited by Master_Scythe, 07 September 2017 - 09:58 AM.