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Old 20-08-2010, 14:37   #1
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Microwave, Inverter and Amps

Hi! I have a Freedom 25 Inverter/Charger on my boat and an old 1987 Lippon "go anywhere" microwave. At times, when I use the microwave while plugged in, the amp meter usualy goes up to about 11 amps and stays constant. However, sometimes, the amp meter will go back down to about 1 or 2 for a couple of seconds, go back to 11 for 10 seconds or so, go back to one, and so on. I thought the microwave might be the issue since it is so old and it didn't seem like it was heating up food as fast as before. So, I tried this with a new kenmore microwave (that used 1 instead of 12 amps) and it went back and forth as well.

I am wondering if the amps jumping back and forth is normal? I would think that a microwave would keep using the same amount of power while it is running. But I could also see the microwave cutting down the power at times while running. I am kind a little worried some of the wiring or inverter may be having problems. Any thoughts?

Thanks!!!
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Old 20-08-2010, 14:42   #2
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Its normal for the thingy which makes the radiation to cut in and out.
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Old 23-08-2010, 09:41   #3
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It is not normal for the magnetron to cut in and out unless you select a power setting other than 100% or your using one of the preprogrammed cook/defrost settings. In manual mode and using the default 100% power setting, you should see a steady current draw.

Eric
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Old 23-08-2010, 10:00   #4
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Thanks for the responses. We are running the microwave at 100% and it is occasionally cutting in and out. I was heating up the same cup of water to test it. Most of the time at ran at 12 amps but sometimes it bounced back and forth. The same thing happened for a new unit and our old one, so I didn’t think it was an issue with the microwave. I can't figure out why it would bounce back and forth at times but not others.
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Old 23-08-2010, 10:08   #5
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It's the magnetron cutting in and out regardless of the 100% setting. There is nothing else with that much current draw that it could be. For a new microwave, I doubt there is anything wrong. Its just how your microwave was designed to function.

Microwave magnetrons are either on or off. This is how the power setting on a microwave is done. The lower the power setting, the lower the percentage of time that the magnetron is on over whichever time you set. The lower setting allows the heat generated by the waves vibrating of the molecules to transfer their vibration to adjacent molecules. Vibration at the molecular level is of course heat. This provides a more even heating since microwaves do not heat all foods evenly.
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Old 23-08-2010, 10:33   #6
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Quote:
Originally Posted by msulc View Post
Hi! I have a Freedom 25 Inverter/Charger on my boat and an old 1987 Lippon "go anywhere" microwave. At times, when I use the microwave while plugged in, the amp meter usualy goes up to about 11 amps and stays constant. However, sometimes, the amp meter will go back down to about 1 or 2 for a couple of seconds, go back to 11 for 10 seconds or so, go back to one, and so on.
!
If you are plugged in the 12v amp meter should not budge at all because of the microwave. If you are not plugged in and using 12v through the inverter the amp meter should show about 90 amps!!
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Old 24-08-2010, 10:14   #7
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This is obviously AC current you are monitoring but is it on the shore power input to the charger/inverter or the output to the microwave? If it's on the input, it may just be normal operation of the charger/inverter or a problem with it or the shore power wiring. You can easily tell by the sound of the microwave when the magnetron cuts on/off during less than 100% power setting. Heat your cup of water up on 80% power and you will hear the maggie cut on/off. Now go to 100% power and listen. It should be on constantly. By the way, microwave ovens do not work very efficiently on inverters with modified sine wave outputs. See this article for more info on this.

Eric
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Old 24-08-2010, 10:39   #8
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Could it be that the current draw by the m/wave is not as high as the inverters "load-seeking", or idle-setting. Can't remember off-hand what the range of amperage levels could be set at.
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Old 24-08-2010, 11:44   #9
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My microwave run tru the inverter uses 100 amps DC steady
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Old 24-08-2010, 19:00   #10
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At 12v, that would be 1200 watts. When on shore power with the inverter being supplied it's power from the charger and not the batteries, the current from shore power would be 10 amps (1200 watts at 120vac). Of course, there will be some loss due to the inefficiency of the inverter which will change these power requirements somewhat.

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Old 24-08-2010, 20:08   #11
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I have run the mircowave often from the inverter of course only for a short time
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Old 25-08-2010, 12:13   #12
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So ignoring ineffeciencies running the 1200 watt microwave off an inverter would draw 100amps. Running for 5 minutes would consume 8.3 amp hours? This is precisely what I want a microwave on the boat for.
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