Microwaves on inverters.

doughere wrote:
I have a unit with 1500 watt microwave and would like to be able to use it occasionally when dry camping (10 min or less at a time). I plan to use a 2000 watt pure sine wave inverter. Also plan using it on a 900 watt coffee maker (about 15 min a pot). Anyone have any experience with this setup?

Thanks,
Doug

Yes it works, been doing that with MW, kettle, and toaster for the last ten years--BUT:

- A "1000w" MW requires way more than that for input (see the label on the back for input required) might be 1500w.

So--what do you mean by "1500w"??? If that is the cooking size of the MW then it will want more than the "2000w" inverter can do (which also will have lower than that wattage as its "continuous" rating.)

You go by the "divide by 10" rule for your DC amps draw with the inverter. 1500w would be 150 amps draw, and 1200w would be 120a, etc. The 900w coffee maker would be 90 amps draw.

Now you look at the draw from a MW when using PSW or when using MSW inverters. First the MSW inverter needs to be a robust type that can run motors with starting surges. They exist, so assume you have one.

Also assume your MW is less than 20 years old so it will run on MSW. Some older MWs will not run at all on MSW. If it does run on MSW, it will run at less power and take a little longer to do the job than a PSW that will run the MW at its full power. If it can barely run, it will groan and moan, so make sure the MSW power is well over what the MW needs as a minimum so it runs ok but just "slower".

What that all leads up to is that the same "1000w" MW will pull 150 amps with PSW, but only about 120a with MSW. (It works out that the longer time with 120a is still fewer AH than the shorter time at 150a, but that AH diff does not matter much in the big picture of your whole daily AH use)

Note that the coffee maker will be the same 90 amps on MSW as on PSW because it is not motor driven.

-Now the coffee maker. 90a for 15 minutes can be an issue. I used a 90a kettle for a single cup at a time taking 3 minutes to boil. Three cups in succession over about an hour and a half in the morning. Never a problem until I got AGMs. After a year of maybe 36 times doing the three cups thing (using three days a month), the AGMs have started acting up.

It turns out they might have warped plates or something that get back to normal at lower draws of say 30 amps, but now they don't like the high amps draws for very long. I can do a single high amps draw no problem, even a second, but a third one and the AGMs collapse. The inverter low-voltage shut down happens. So I don't do the three cups with the kettle anymore, I do the coffee water on the stove. I still use the MW And toaster as one time shots, no problem

So the coffee maker at 15 minutes is one shot, but is a long time. I don't know how AGMs would like that. I was always able to use the MW for say 10 minutes and then right away for another 5 minutes when I had Wet batteries. Say DW inside does two spuds for 10, then frozen veg for 5 with me doing steak outside on the RVQ, onion/mushroom garnish on stovetop.
(Drat--now I want to go camping!)

So yes, you can do it ok if you really have a 1000w MW, not a 1500w one, and you have about 400AH of batteries for the 2000w inverter, and if those batts are Wet, not AGM. You might be able to do it with AGMs a few times and get away with it.

It might be that there was something wrong with my particular AGMs that made that happen, and it would not happen with anybody else's.
Don't know about Li batts. ( If you can afford Li, why are you in an RV instead of at the Sheraton? :) )