Microwaves on inverters.

4x GCs will be adequate. MW and coffee pot are usually limited time use. For example the MW could draw 150A for 10 minutes. That's less that 30Ah that needs to be replaced.

No issue with my large MW and 2000W inverter. No idea why others are concerned about MW surge which would be a concern with motor appliances.

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? :) )

I used a 700 watt microwave & a 5 cup 600 watt drip coffee maker with a 1500 watt PSW inverter on a pair of 232 amp hour 6V golf cart batteries, recharging with between 360 & 420 watts of solar. There were days that because of clouds, rain, etc that I skipped the microwave use, but almost always made the pot of coffee. Used 6-8 amp hours for the coffee. As long as you monitor the batteries & have a means to recharge them, it will probably work. Some microwaves are pretty inefficient, which could present a problem.

That said, when the microwave died, I replaced it with a 950 watt Panasonic inverter microwave. The advantage of the inverter type microwave is when you dial down the power it actually drops the input wattage. At lower power levels, a standard microwave runs off & on at full power. When the batteries are low, I can dial down the microwave to as little as 300 watts. It also does a much nicer job of defrosting - no cooked edges of food.

4x GC2 and 400 watts solar to go with that inverter will work fine.
Lithium is great but not necessary. If you go lithium make sure the parallel capacity is 200+ amps.

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

run our microwave quite often on an inverter. you will need enough battery and big short cables from battery to inverter.

Now one thing to consider, which we did was to toss the original microwave in the donate pile and buy a panasonic true inverter microwave. It's operation is much different than traditional microwaves. when in partial power mode it doesn't cycle between 0% and 100%, it actually runs at the % set. So.... if you set it to 50% that's what it runs at continually. Ours is a 1500watt microwave and I run it easily on a 1000W inverter if power is set to 50% or less. At 50% power it does NOT take twice as long to heat something, more like 25% longer.

I also have a hotel type keurig that draws 900W and we run it off the 1000W inverter with no problems either.

for this type of draw I'd recomend either 4 GC2s or a bank of 12V. GC2's aren't great for large current draw and have high internal resistance compared to a 12V jar. So with only 2 GC2's your inverter may shut down when batteries are below 75%ish SOC. With 4 GC2's it should work down to 50%. I run 4GC2's, with only 2 it only worked with batteries charged above 75% or so. A few others have had similar experiences.

Our Winnebago has this setup as a stock configuration. 2KW inverter and household microwave (not sure of the wattage). It works fine. We also use a K-Cup machine in the AM. BUT, I have 800Ah of batteries (I'm sure you could do with half that). Another tip I used to perform when my setup was less than this, heat hot water on your propane stove and pour it into the k-cup (or standard coffee maker). It takes a lot of juice to heat that water. If pre-heated, the unit only runs a pump.

Shot-N-Az wrote:
I suck at math, and I’m no electrician, but real world experience is that I can microwave on my inverter but it takes a lot longer than normal.

Is that a sine wave inverter?
Very common for a MSW to cook slower as the peak wave voltage underdrives the megatron.

I have four Trojan T125 batteries and a 2000W inverter and often use our 1200W microwave to warm food for lunch or a cup of hot water, usually for no linger than four minutes at a time with no problems.

Bill

time2roll wrote:

Shot-N-Az wrote:
I suck at math, and I’m no electrician, but real world experience is that I can microwave on my inverter but it takes a lot longer than normal.

Is that a sine wave inverter?
Very common for a MSW to cook slower as the peak wave voltage underdrives the megatron.

People might remember my tests on that for PWS vs MSW to heat a cup of water to a certain temp in the MW starting from the same cold temp. Yes it took longer with MSW to reach that temp.

However, in real life cooking a spud, Eg, you stick a fork in it to see if it is soft yet. How soft is soft? It turns out that you can stick the fork in at about the same time with MSW. It is soft "enough".

Same with frozen veggies. How soft is soft enough? Turns out you can over-do it with PSW and that the MSW for the same time is "enough".

So this is not a lab test using instruments.

If you are heating something and you need to let it cool down before you can eat it, you just wasted AHs. However some cooking does require you to heat it up just so, to "bring out" whatever, even if you then need it to cool before you can eat it and not burn your mouth.

I had no trouble with the 2000w MSW inverter to do everything with a newer MW. However, this 1991 MH has a 1991 Dometic "RV MW" that will not run at all on MSW. Turns out it runs perfectly on PSW. I had the opportunity to get a PSW 2000w so I did instead of swapping out the 1991 MW.

Several different brand, newer (say 2003 on?) MWs do run on MSW just fine except "slower" (when lab testing per above), when we tried them out in various RV set-ups in the slide- in camper and 5er we had.

It is only when you are operating on the margins that any of this matters. If you have lots of battery and proper size inverter (MSW or PSW) with proper wiring, you can run any newer MSW MW of the matching watts and not notice any real difference for most jobs.