OT Microwave oven melt down

moonlight machine · Mar 10, 2020

I was working in the shop last night. Welding grinding all the usual. I started to smell something strange,looked around, did not see anything and went back to work. Later I saw that the clock was out on the microwave. I looked inside and the bag of chips that was in there so a mouse would not chow down on them was reduced to carbon. The coating on the glass was melting off, there was evidence of smoke coming out the vent. The labels on the back were melting and dripping down. The clock was working and all was well at 7:00 by 11:00 it was done. The thing started on its own and cooked til it melted down! WTF! Anybody see this before?

Hardplates · Mar 10, 2020

pictures?

moonlight machine · Mar 10, 2020

Hardplates said:
pictures?

It went in the dumpster last night and they picked up this morning.

Gordon Heaton · Mar 10, 2020

Never, ever heard anything like it! Glad you were there.

JST · Mar 10, 2020

Have not, but those things are controlled by microprocessors, programmed by folks in china who want to get it done and get paid, so there is certainly no guarantee it will be bug-free.

And parts fail, also.

Odd thing is that they have , in general, fuses in them, so if they go crazy and draw too much current, the internal fuse should blow and stop it. They blow when you do NOT want them to..... evidently they do not blow when they should, although the thing might have just been working as per normal, aside from it starting without a command.

Another thing.... they produce radio waves, and the chamber itself does not absorb much power, the cooked material is supposed to absorb nearly all, only you didn't have much if any effective "cooking load".. That one might not have been made to be safe when nothing is inside to absorb power. They can fail in "interesting" ways in those cases, where "standing waves" build up in the chamber due to the power not being absorbed by a "cooking load".

None of this excuses the thing turning on by itself.

1 Jaw Chuck (Chuck Evans) · Mar 10, 2020

Seen it happen. My father was using the microwave (1999) and it overheated and caused a kitchen fire.

Did not start on its own however.

Chuck
Burbank, CA

PeteM · Mar 10, 2020

Maybe something an accumulation of grinding dust or welding fumes made a connection??

My own microwave story is that when mine died, I took it apart. The maker had kindly put a schematic inside. Problem was, that schematic had been almost completely toasted a nice burnt brown by the time I needed it.

Gordon Heaton · Mar 10, 2020

PeteM said:
Maybe something an accumulation of grinding dust or welding fumes made a connection??. . .

I've wondered about that myself. I have a microwave in the shop, sitting on top of the mini-fridge. Its only 5 ft from the pedestal grinder.... maybe I ought to take a look inside!

moonlight machine · Mar 10, 2020

It did not pop the breaker, but it was totally dead when I got to it so it may have had a fuse in it. I thought about taking it apart for about 1/10th of a second, but it smelled so bad I just wanted it out of the shop. Even now 24 hours later this place just reeks!

PeteM · Mar 10, 2020

The one that died on me had both an electrical fuse buried inside and a thermal breaker. Thermal breaker was my problem - been running several years since replacing it.

GregSY · Mar 10, 2020

Microwave ovens...I read an interview with some woman who owned one of the first microwave ovens ever built. It was ancient but still worked. Turns out her father was at Raytheon and one of the engineers who 'invented' it. The one she had was like the 4th ever let out the doors....as you can imagine it cost a fortune and her mother had a heart attack when her father brought it home, so proud that his device was actually being sold on the market. Anyway, they attributed the reason it still worked to the fact that Raytheon had built it with an aerospace radar-quality tube, or some such. As the product became more refined and cost-reduced...they realized they could cut a lot of corners on that front.

My sister-in-law had some old microwave...notable for the fact that she would routinely leave metal spoons in it to no detriment.

JST · Mar 10, 2020

moonlight machine said:
It did not pop the breaker, but it was totally dead when I got to it so it may have had a fuse in it. ......!

Well it failed safe, so it met one requirement of UL. I had thought you meant it was still running and trying to cook itself when you got there.

There should have been a thermal sensor in it also, which may have opened. The transformers in them are super-cheap and limited duty cycle, so if it had been running long enough, it may have tripped the thermal in the transformer.

JDennis · Mar 11, 2020

GregSY said:
My sister-in-law had some old microwave...notable for the fact that she would routinely leave metal spoons in it to no detriment.

I saw something on TV or Youtube a few years ago talking about this. They determined that with spoons or butter knives you were generally safe leaving them in because the rounded corners and continuous surface would not allow the induced current any easy exit point, where as sharp corners, points or gaps of a fork would arc and be a fire hazard.

gustafson · Mar 11, 2020

young and broke I would bring my own mac and cheese to work and heat it up in the microwave.

put it in one day and sound like the saran wrap expanding, but all the Korean women I worked with were in a tizzy.

I turned around and little lightning bolts were flashing down around the edge of the plate

Seems I had 'inherited' one of my mother's old gilt edged plates and the microwave took exception

Didn't hurt the microwave any but did blast some of the gold off of the plate

GregSY · Mar 11, 2020

I used spoons as an example...but she would leave anything metal in there.

kustomizer · Mar 11, 2020

The one in our motorhome started itself when we connected the rv to land power, it was working on melting down while we were putting out awnings and hooking up water, it filled the rv with toxic smoke and was growling like a dog with a bone when we opened the door to go in. We unhooked the power to the rv, unbolted it, took it out, and the rv stunk for weeks.

dsergison · Mar 11, 2020

metal generally is fine if it's thick enough to carry the induced current. metal racks are in more than a few models. I microwave utensils all the time.

bhigdog · Mar 11, 2020

dsergison said:
metal generally is fine if it's thick enough to carry the induced current. metal racks are in more than a few models. I microwave utensils all the time.

Try nuking a raw egg sometime.............Bob

Mark Rand · Mar 11, 2020

Our 35 year old microwave oven occasionally trips the RCCB/GFCI breaker supplying the kitchen. Don't know if it had a problem all along or it developed one after I retrofitted the breaker last year. I've been thinking of getting a replacement that has a higher output and a built in grill, but the old one, with its clockwork controls still works as designed.

MetalCarnage · Mar 11, 2020

moonlight machine said:
I was working in the shop last night. Welding grinding all the usual. I started to smell something strange,looked around, did not see anything and went back to work. Later I saw that the clock was out on the microwave. I looked inside and the bag of chips that was in there so a mouse would not chow down on them was reduced to carbon. The coating on the glass was melting off, there was evidence of smoke coming out the vent. The labels on the back were melting and dripping down. The clock was working and all was well at 7:00 by 11:00 it was done. The thing started on its own and cooked til it melted down! WTF! Anybody see this before?

This happened around the time of the daylight savings change? Is it possible that someone tried to change the time on the microwave and inadvertently set the timer to run instead and walked away? Let's see, thought he was changing the "time" to 11:00 and started it running for eleven hours straight. Makes more sense to me than starting on it's own.

FWIW

-Ron

OT Microwave oven melt down

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