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Old 22-10-2016, 08:33   #1
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Microwave Time

For some reason the microwave when running off the inverter has become some type of time machine. One minute of microwave time when run off the inverter is now 15 seconds of real world time and it doesn't seem to heat anything even though it seems to be using the wattage power. It runs normal if I run it off the generator or shore power.

Anyone have a theory? Everything else seems to run normal off inverter power. I was motoring so it isn't a battery power supply issue and the low voltage alarm didn't occur.
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Old 22-10-2016, 09:21   #2
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Re: Microwave Time

Is your inverter a pure sine wave or modified sine wave output? Some power supplies within devices are very critical about the quality of the power source. Not all inverter outputs are created equal. If the microwave works fine on all other sources it does point to your current inverter. Can you measure the AC voltage while the microwave is running? Can you measure actual D.C. Voltage at the inverter while microwave is running?


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Old 22-10-2016, 10:10   #3
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Re: Microwave Time

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Originally Posted by sailorboy1 View Post
For some reason the microwave when running off the inverter has become some type of time machine. One minute of microwave time when run off the inverter is now 15 seconds of real world time and it doesn't seem to heat anything even though it seems to be using the wattage power. It runs normal if I run it off the generator or shore power.

Anyone have a theory? Everything else seems to run normal off inverter power. I was motoring so it isn't a battery power supply issue and the low voltage alarm didn't occur.
Sailorboy,

The microwave [and modified sine wave inverter] that came with our boat had the same issue.

The charger in the old modified-sine wave inverter finally started dying, so I replaced the inverter with a pure sine wave model [with a higher charging capacity as well.]

The microwave now works just as well on the new inverter as it does on shore or generator power.

My research revealed some microwaves are more sensitive than others, but all I needed to replace was the inverter... [the most expensive option, of course...]

In case this helps.

Cheers! Bill
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Old 22-10-2016, 10:16   #4
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Re: Microwave Time

It of course would seem to be the inverter. The microwave did of course work fine in the past (the few times I used it). Wonder if this is also related to why it seems the charger uses a lot more power than expected for its' output.
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Old 22-10-2016, 10:22   #5
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Re: Microwave Time

Our's does the same thing. Unless I'm just heating up a cup of coffee or tea for 2 minutes or so, we always run the generator when cooking a meal or something more substantial like a baked potato. Otherwise, the microwave seems to heat up rather than the food object we're trying to heat. Our small microwave is run off a 2500w inverter.
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Old 22-10-2016, 10:53   #6
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Re: Microwave Time

A sine wave develops 1.41 times more voltage at its peak than a modified square wave of the same energy whereas a modified wave is broader timewise thru the middle of its upper area. The area under each is the same and therefore the available energy is also the same.
That's why a light bulb on a modified sine wave looks just as bright as on a pure sine wave source.

A microwave oven rectifies the PEAK voltage and applies it to the Klystron which makes the waves.
When it receives less voltage but over a LONGER TIME each cycle, it doesn't produce as strong microwaves, but it draws a great amount of current and overheats itself.

Think of the microwave oven running at ten thousand RPM in first gear on a MSW instead of full speed in 5th gear.

Sine wave inverters are much more affordable these days.
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Old 21-03-2018, 10:19   #7
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Re: Microwave Time

Well this is an old thread but:

I was looking into replacing my charger/inverter because:

1 - it wouldn't run the microwave and it was a PITA to run the generator just to run the microwave (and the generator was broke for 2 months recently)

2 - the voltage from the generator is lower than shore power and that really seems to reduce the charge amps resulting in having to run the generator longer than I want to listen to it

3 - the charger doesn't have the settings I want and goes into float too early

That got into the whole pure sine wave verse modified sine wave decision ($300-400) with the manufacturers saying that a modified sine wave would run a microwave. But thats what I have now and the microwave wasn't working. But since it have been 1.5 years since I started this thread and I hadn't even tried to run the microwave off the inverter since then I tried it. You know what, it worked just fine. So I thought maybe somehow it mattered if the engine was running as that it was the last time I had tried to do it (I couldn't really think of why that would be) so I started the engine and tried it again. And again it worked just fine.

So now the whole replace the charger/inverter is up in the air as to whether it is worth the cost of doing and if I do whether to get the pure sine wave unit of not!

If only there was a place to get someone else to do all the pros/cons
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Old 02-04-2018, 13:35   #8
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Re: Microwave Time

If the timer is off it's the cycle rate of the inverter. If you have an 120v electric clock, it should be off the same amount.
Pre computers, I was on a ship where some engineers were speeding up the generators to change the cycle rate. The ships clock master was AC and all the client clocks ran fast about 10%. Before being busted, caused by us star shooters when comparing the chronometers, engineers last act before going off watch was to reset the generators.
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Old 02-04-2018, 14:02   #9
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Re: Microwave Time

Microwaves no like modified sine.
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Old 02-04-2018, 14:04   #10
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Re: Microwave Time

SB
Not sure what charger/inverter you should get but it sounds like it is time to throw out the microwave as you haven't used it in 1.5 years. We got rid of our microwave because we hardly used it and had better things to do with the space.
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