Which mini microwave WORKS with a Freedom 20 Inverter?

capta · Nov 6, 2016

We run our microwave on a modified sine wave inverter all the time. If that is a 900 watt unit, at 120 volts, the Freedom 20 (a 2 kw unit?) should easily power that microwave, though at a reduced power because of the modified sine wave, which is to say it will take longer to cook things than expected. Don't throw the baby out with the bath water just yet. Look for another reason why it won't work.

Maine Sail · Nov 7, 2016

mz4wheeler said:
Bummer: I just dropped $130 buying this nice little microwave, only to discover LATER that it doesn't work with my Freedom 20 Inverter. Dang!!!

Obviously, I don't need a large microwave on my boat. This one was just .7 cubic feet, designed as a corner unit, and neatly fits in my galley. It's all great, except it doesn't work.

Since I bought the unit, I found out that my inverter produces a "modified sine wave", not a TRUE sine wave. OK: Lesson learned (the hard way).

Here is my question: Does anybody know, FOR SURE, that their little microwave works with their modified sine wave inverter? Does some list exist somewhere what "certifies" that microwave model XXX works for these types of inverters? Do you have a Freedom 20 inverter, and you have a .7 cubic foot microwave that works? What model???

Thanks!

Microwaves generally dislike many MSW inverters and yes some won't work at all depending upon the design. No matter what microwave you use it won't perform as well as it would with a Pure Sine inverter.

Microwaves are fairly complex using an internal transformer to bring 120V to approx 1800-2000V then it uses the magnetron and some diodes or fets, which gets rectified and doubles the voltage again to develop the rest of the voltage pushing it upwards towards 4000V +/-.

Some microwaves will even make really funny noises when working off MSW and some will simply burn out prematurely. Some inverters sold are actually square wave and most microwaves won't work at all on this. MSW tries to make the wave look more like power company but the peak voltages may not line up hence the different noises and lower performance..

What about battery input voltage? Microwave ovens are particularly sensitive to peak AC voltages. Higher voltages mean better cooking performance. MSW inverters do not deliver the same waveform "peak" voltages that the street does or a pure sine inverter does. Inverters try to maintain a peak voltage on output but they are directly affected by the DC input side that is powering the inverter. Couple MSW with low battery voltage and we have lower microwave performance. If your microwave works with MSW it will take longer to do the same job.

Most microwaves will "work" with MSW, but at a reduced potential, and they can die an earlier death. At best it will just take more time to do the same job that a Pure Sine inverter would do (MSW often between 15 & 25% less efficient at actual cooking performance). I've have run multiple tests using the best MSW inverters against even cheap Pure Sine inverters and there really is no comparison in cooking speed between the two. The microwave when run off pure sine also sounds healthy and does not sound "straining" and "buzzy" when operating off MSW.

Maine Sail · Nov 7, 2016

mz4wheeler said:
Well, it works at home. It works with shore power. Under inverter, it SEEMS to work... Lights up, turntable works, digital controls all look good, its just the magnetron doesn't engage. Looking at the inverter control panel, it doesn't draw the amperage I would expect for 800 watts. It's definitely not the inverter, all other appliances work fine (hair dryer, etc.).

Remember an 800W microwave is the cooking wattage. It will be drawing considerably more from the wall probably somewhere around 1350 +/- watts from street power..

BLOWINWIND · Nov 7, 2016

Think clearly on this. The label on the MW front shows Cooking watts.The Manfg sticker shows Amps needed from 120v wall outlet, or shows overall consumption of 110v , or ie =total watts. Usually 700,800,900,1000 Cooking watts still take
1000 watts out of wall even if cook power is 700 watts. So you would be better off to get a 2,000 Watt inverter--EO.

Dig this--a microwave tube returns to Ground (or Negative). Therefore the Inverter and Oven must all be connected to the same ground. You can't even run a MW with no ground pin, missing ground or not grounded outlet at home.

Joe2954 · Nov 7, 2016

I installed a 0.5 cu ft Tappan Microwave in 2006, rated at 500 watts microwave power with a demand of 850 watts. I initially was able to get it to run with an 800 watt (1200 watt surge) automotive inverter. It now starts and runs fine powered by an older Balmar 2000. We don't always run the engine at the same time, but when we do there is a noticeable improvement in MW power.
We are also able to run a small window size 5000 BTU AC with mechanical controls with the inverter. However, the AC will not restart after running until it has bled off the compressor.

BLOWINWIND · Nov 7, 2016

Ground ? ALL Same ?

BLOWINWIND · Nov 7, 2016

I was USAF (ours), (UGBC.) Big ground radar tech. 1/4 is about right wave etc. I would say, I guess may me the answer.
Remember where the electrons are supposed to go. Ground. Throw tome neon bulbs inside it and see if they flash -on and off.
Disconnect the ground in the house,or use an extension cord 2 wire OMG, it Doesn't work ?
Good Luck

Maine Sail · Nov 7, 2016

BLOWINWIND said:
I was USAF (ours), (UGBC.) Big ground radar tech. 1/4 is about right wave etc. I would say, I guess may me the answer.
Remember where the electrons are supposed to go. Ground. Throw tome neon bulbs inside it and see if they flash -on and off.
Disconnect the ground in the house,or use an extension cord 2 wire OMG, it Doesn't work ?
Good Luck

A microwave that required the protective Earth/grounding wire (green), in the 120V operational path, would not meet US codes because the green/grounding/Earth wire is 0V/Earth referenced unless a fault has occurred.. In other words reading continuity between the ground prong and neutral prong, when the unit is not plugged in, would violate NEC and US safety codes.

The microwave operates on the Black/Hot wire and White/Neutral Wire. The green wire is Protective Earth/Ground and is there to bond the metallic parts of the case to the Earth should a failure occur in the microwave that shorts to the metallic case. If this happens the green wire will provide a path to Earth and trip the fuse or breaker to save a human from being shocked.

There are plenty of improperly-wired boats, RV's and older houses out there where the microwaves work just fine on a two wire (hot/black and neutral/white) system. While it is really not advised to run any appliance as two wire, without ground, the protective Earthing/grounding wire is not required for a microwave to function.

Ken Cross · Nov 8, 2016

It seems to me that if the microwave oven required the earth ground, it would trip the GFCI.
I certainly wouldn't be able to use it in our kitchen at home or on the boat.
Ken

Benny17441 · Nov 8, 2016

See if you can find the wiring diagram for the unit in the odd case that a safety switch may have been incorporated on its designed circuitry to protect the magnetron against inadequate power.

Disregard more than likely it would be a design feature at the magnetron. Well, it is what it is so, I would suggest picking up a small cheap microwave at a flea market for around $10-$15 for use when away from the dock.

centerline · Nov 8, 2016

I believe you will find its more of an issue with the power source than it is the microwave oven.... test the inverter output power and you may find its either weak or its dirty power.... just because the power being delivered thru the device will run a component that operates directly on the "short circuit" principal like a heater or hair drier doesnt mean it will operate something more sophisticated like a microwave oven...and may actually be harmful to some components
Ive had the issue a couple times, and even to where the oven lights, timer and the rotating plate would function fine, but it wouldnt heat anything.... what I did was get a line conditioner, and plugged it in to the source power, then plugged the microwave into the line conditioner... and it works fine. its how I currently run the microwave in our toy hauler off the small genset... clean power is usually the answer..
going thru the line conditioner is also much safer when we need to plug our laptops in, because dirty power can damage chargers, and other electronics.

a line conditioner will take unstable, noisy power (dirty power) and stabilize it to produce clean power that is easily used by sensitive components, such as a microwave.
electricity can be unstable in several ways. voltage spikes/drops, or an unstable wave form... and then there can be other unwanted noise within the power that is caused by other reasons. a good line conditioner will clean up most problems.

Robin S · Nov 10, 2016

For the benefit of this group and Google searchers everywhere, here's what I found at home with my microwave.

It is rated at 750W cooking power. Input power is marked at 120v, 12A. (That's 1440 watts input, by doing the math) Note that input power numbers are always "worst case" and often can be less. A desktop computer would be noticeably less, a laptop pretty close. The desktop would have to have all slots filled with cards, etc, to reach the rated input power numbers. A laptop doesn't have many options. Something like a microwave or coffee maker will be close to rated power.

Here in SE Michigan, DTE Energy has available a "Power Bridge" device that talks with your smart power meter and gives you instantaneous power usage, plus graphs over time, history, etc. A smartphone app lets you monitor it from anywhere. Actually pretty cool ...

By noting my house baseline power usage, then running the microwave, it draws 1354 watts of power. The light bulb uses 30 watts alone, and is on while cooking. On a boat, I would remove the bulb, if equipped. Then total power was 1324 watts, or 110 amps at 12 volts! I would expect the trouble is the modified sine wave inverter just not being accepted by the MW. Some kind of power conditioner/filter is a possibility, but not cheap to be effective

BLOWINWIND · Nov 25, 2016

Sorry -- There is such a lack of proper information it is baffling. A clue is as the nameplate last line says ." WITH GROUNDING." A microwave uses the ac + and - via a doubler and transformer to make up the NEGATIVE Hi voltage for the microwave tube. (See if you can find a ground.) The Anode of the TUBE, THERE FORE, is GROUNDED ----AND THAT IS THE CABINET GROUND, NOW IF I DISCONNECTED, THE TUBE ANODE, EVERYTHING WOULD WORK EXCEPT THE MICROWAVE AS IT HAS NO MINUS path For conduction of the -2400 . ( + -)

I think I'm giving up----when I saw the author state the Freedom draws over 100 AMPS --WE ARE NOT ON THE SAME BOOK OR PAGE !

Which mini microwave WORKS with a Freedom 20 Inverter?

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