Roadpro 2500 will not operate for more than 2-3 minutes.

Most food cooking directions are based upon a 1100 watt microwave oven output..
Since you didnt specify, I am guessing you have a 700 watt oven
You can roughly adapt cooking directions by multiplying times 1.6.
So if directions say 6 1/2 minutes at 1100w, cook for 10 minutes 24 seconds, or 10.4.minutes [roughly]
Here is a list of other oven powers
600. 1.8 times
700 1.6 times
800 1.4 times
900 1.2 times
1000 1.1 times

Of course, this is only a rough scale, microwave cooking times always vary from machine to machine. Always pay close attention when cooking.

There is a method described in this article that can be used even if you can't find a manual.

https://www.epicurious.com/expert-advice/how-to-find-adjust-wattage-power-of-microwave-oven-article

Quoting: "To find an approximation of your machine's wattage, fill a microwave-safe liquid measuring cup with 1 cup cold water. Microwave on High and keep an eye on it, noting how long it takes for the water to come to a boil:

• 1 1/2 minutes: 1,200 watts
• 2 minutes: 1,000 watts
• 2 1/2 minutes: 800 watts
• 3 minutes: 700 watts
• 4 minutes: 600 watts

you need at least a 1900 watt inverter with a fully charged battery to run a 900 watt microwave,it uses 900 watts to make microwaves and it uses 700 or so to run everything else.

you can get the manual in this link

http://kitchen.manualsonline.com/manuals/mfg/sharp/r820bk.html

engine has to be running with some high wattage items if your engine was running then your inverter is defective.

how do i set my hamilton beach 900 watt microwave to 50% power

From what I could find, it should be 10 1/2 inches in overall diameter.
meowpfttpftt

I have had this happen a few times.

Sadly replacement is the Best option.
Repairs can be %75 the cost of a new one.

The best invert we have been using is a Pure Sine 1500 watt inverter.

Sad news but hope this tip helps.

R/
David

If you are referring to the RoadPro RPPI-250

2000 Watts Continuous Power

2500 Watts Power Output @ 10 Minutes

5000 Watts Peak Power Output.

A small fridge will use about 500 -700 watts, with startup wattage at around 2000watts.

So, a dorm fridge will work fine.

the RoadPro converts DC to AC voltage, so a regular 120 volt dorm fridge will work.

You probably have a bad damper switch, damper motor or damper. See the attached sample drawing. You can order parts for Sharp models from Tritronics at http://www.wehaveparts.com.