Dometic Microwave On Its Way Out? - Fiberglass RV


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Old 06-07-2010, 09:16 PM   #1
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Trailer: Bigfoot 21 ft Rear Bed
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When I use the Dometic microwave in our Bigfoot 21RB it seems to start OK but the light inside soon dims and the fan slows down. I don't recall it doing that before. Actually, I don't ever even remember using it. Is this normal or should I have it checked out? Oh, it heats a cup of water in about a minute and the platter rotates.
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Old 06-08-2010, 05:50 AM   #2
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Sounds like you have a loose electrical connection and are loosing voltage.

Put a meter on the 115v line and see if it drops when you start it.

Bill K

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When I use the Dometic microwave in our Bigfoot 21RB it seems to start OK but the light inside soon dims and the fan slows down. I don't recall it doing that before. Actually, I don't ever even remember using it. Is this normal or should I have it checked out? Oh, it heats a cup of water in about a minute and the platter rotates.
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Old 06-08-2010, 04:46 PM   #3
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Steve, do you think it's possible that where you are using it there are other electrical appliances also being used. Did a clothes dryer or electric saw (for example) kick in somewhere on the same grid? Did you test it at your home? By your description and your last sentence it does sound like a draw on the grid and not your microwave.
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Old 06-08-2010, 05:57 PM   #4
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I measured the voltage inside the trailer at a couple of the electrical outlets and get 119.3 V without any appliances on. When the microwave first starts the voltage drops to 116.7 V and then down to 101.8 V when it bogs down (light dims and fans slows) after about 3 or 4 seconds. The voltage returns to 119.3 V when it stops. The trailer was hooked up to a 20 amp circuit in my garage using an extension cord. I'm lost. Any ideas?
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Old 06-08-2010, 06:07 PM   #5
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What is the wire gage of the extension/ if it's a light-weight (14 or 16) then what you have happening is heat in the cord which increases resistance.
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Old 06-08-2010, 07:16 PM   #6
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What is the wire gage of the extension/ if it's a light-weight (14 or 16) then what you have happening is heat in the cord which increases resistance.
I don't know the gauge of the extension cord but when the trailer cord was hooked up to my Honda EU2000iac the same thing happens. Looks like the next step is to take the microwave out of the trailer and hook it directly to a house outlet. ????
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Old 07-23-2011, 11:46 PM   #7
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Name: David
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I have nearly the same problem. and have had since new. Described the problem to warranty people and they just lookat me as if they didn't understand. They exchanged the microwave for another and the situation remained the same. I measure the line voltage with the machine MW operatating and it will drop from 115V to 107 V when the magnetron cuts in and then the fan drags down to about half speed. I worry that the magnetron may not be cooled properly. Checked all cons. through the breaker box and nothing found. This happens 70% fo the time when in a campground. It is more rare than not that the fan will stay up at speed when the Magnetron cuts in.
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Old 08-03-2011, 11:34 AM   #8
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I'm having this same issue that I've been working through for the last couple days and believe I've found the answer, although it's yet to be definitively tested.

It looks like it all comes down to the extension cords. I've used two different microwaves and they both act the same. I used my Kill-a-Watt to determine that both microwaves were using the same amount of power (approx. 880 watts and 9.2 amps). For me, I believe it's going to come down to the gauge of the extension cords, in part, due to the length of the run.

Here are a couple of good links to help explain:

* This one is in regards to the wire size for a circuit depending on the voltage, length of the run, amps, etc.. So it should stand to reason that they same would be true of the extension cords too; Wire Size Calculator

So, for me, running copper wire approx. 100 ft, off a single pole, 120v, 20 amp circuit... it says I should be using 8 gauge wire.

* This one is just an overall good read on the subject. The key piece I learned from this one is; "Length - As mentioned above, for every foot that current flows through a cord, there is a voltage loss. For a given current flow, fifty feet of cord will have twice as much voltage loss as 25 feet of the same
cord." There's also a good chart to show the percentage of voltage drop depending on several aspects; http://home.mchsi.com/~gweidner/extension-cords.pdf

I had already replaced circuit breakers, etc. Tonight I'm going to go back to square one and plug the microwave directly into the outlet. If it still happens, I'm going to put a new single pole 120v/20a circuit into the panel and run it to one single outlet using either 10 or 8 gauge wire and see if that resolves the issue.

But this issue is absolutely not due to the microwave itself.

Hope that helps anyone who happens across this in the future. I'll try to remember to update with any findings going forward.
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Old 08-03-2011, 12:31 PM   #9
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Wiring a trailer

We've had three rigs and have added outlets to all of them. We always use 14 gauge (15 amp wire), certainly adequate for an RV microwave. We typically have two boxes on a wire run.

We have had more than one incidence where the screws have loosened within the breaker box. I try to loosen and retighten the screws yearly.

Of course the cord to the box needs to be more substantial, capable of 30 amp service.

We use no extension cords in the trailer; we just put outlets everywhere.
We're up to 9 outlets, planning to add one more for the Air Conditioner when added.

Norm
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Old 08-04-2011, 08:30 AM   #10
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Name: Kyle
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I proved my theory correct last night;

I plugged the microwave directly into the outlet and it did not bog down at all. So I went and bought a 50 ft. 10 gauge extension cord (not cheap, by the way). I also installed a new separate 20 amp circuit breaker leading to a 20 amp GFCI outlet that I'm only using for my microwave. Unfortunately, 50 ft wasn't enough for me. Rather than going out to buy another 50' 10 gauge extension cord, I decided to try it with a 12 gauge going the final 50'.... works perfect!

However, now my AC is on a 14 gauge extension cord and bogs down... DOH! Fortunately all I have to do is repair a 12 gauge extension cable I already have for that one.

So, for me anyway, it was all about the extension cord(s) I was using, taking into account the distance and what was connected to them.

I hope that helps.
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