Mums Microwave died.

Hi all,

We got a call from my (86 year old) Mum today to say that she saw smoke coming out of her microwave so she unplugged it and carried it out into the garden!

It's not a modern lightweight jobby either, a pretty substantial one we bought her around 30 years ago.

Now she knows not to put anything metal in it and has been using it for 30 years (after all), and was apparently, just warming some soup when it happened. The only 'thing' is that she also left a light, clear plastic food tub / punnet in there as well (she didn't spot it because it was transparent) but that didn't seem to have suffered so presumably didn't get hot itself?

Can anyone suggest what happened from this picture (taken looking up inside at the top):?

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Is that circle the output port of the magnetron you can see though the hole?

A question this raises is that are old microwaves a fire risk (and if so why), as ours is probably older than mums was. We did try to find a more colour coordinated microwave the last time we decorated the kitchen but couldn't find anything that was as substantial and capacious without being more complicated or expensive. ;-(

Cheers, T i m

Reply to
T i m
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T i m a écrit :

The magnetron is usually at the side, working through an RF transparent ;window. That looks as if it could be the result of the rusting oven liner, making poor contact with the rest of the lining. That would concentrate the heating effect, causing a blast such as that. Or perhaps a spoon was left in a bowl and that made contact with the lining.

Reply to
Harry Bloomfield

I can't remember what else was inside other than the 'plastic' panel at the top, part of which you saw melted.

Ok.

[1]

I don't think it made a noise as such (although you might have expected it to have done, looking at that damage) and (luckily?) Mum was in the kitchen at the time and although a bit 'mutton' these days, would probably have heard that?

Well, again, I wasn't there so only have her word for it but she assures us that she was just doing what she has always done and because it's (was) a pretty big oven, would have taken a fair sized spoon to have gone anywhere near the sides (and certainly the top) if left in a bowl?

FWIW, we replaced one of the two series 120V (or whatever they were) lamps a few years back and cleaned it out while we were there (there was a fair bit of 'fluff' over things). It amazed us just how well everything was made and how clean it still was (considering it has been used in a kitchen for 30 years). ;-)

Cheers, T i m

[1] "These blast points... too accurate for Sand People. Only Imperial stormtroopers are so precise." By ? ;-)
Reply to
T i m

All cooking devices are a fire risk. Microwaves are massively safer than flame based methods.

Current microwaves are marginally safer due to a HV fuse, but not by much.

NT

Reply to
tabbypurr

And some clothes drying and mobile telephone devices of course. ;-(

Makes sense.

I don't think it's something you hear of much though is it?

Cheers, T i m

Reply to
T i m

It's probably worth getting a new microwave with a metal cabinet rather than plastic. (Re. Fire safety)

Reply to
harry

I had an old philips go like this many years ago. The bloke who condemned it suggested that the rust on the microwave door seals might have changed the cavity perameters enough to cause hot spots to move. I'm assuming he meant standing waves or reflected power back into the magnetron area. It was a strange beast as it had no turntable but a rotating aerial which of course was never as good as a turntable. I cannot see your picture obviously, but there are so many things that can cause reflected power to be in the wrong place, that you may never know. Most things in microwaves are supposed to be non flamable but presumably that does not mean melting will not happen if they get hot enough! I now have a talking one from Cobolt. Brian

Reply to
Brian Gaff

I've never seen one with a plastic case.

NT

Reply to
tabbypurr

When reheating some foods, especially those with membranes such as eggs or potatoes they will often produce mini "explosions" scattering bits of food around the cooker. If a large lump sticks to the surface it can overheat and burn some time later. (You can see some smaller bits in the picture so this has happened in the past). If it sticks to the roof it often wont be noticed but can overheat.

I'm assuming this is a microwave with a roof mounted feed and possibly a stirrer fan such as shown here :-

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and here
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The stirrer fan scatters the microwaves around, some are driven by a small motor, others by a belt from the cooling motor and some revolve in the cooling air. They often stick and debris can build up causing sparking. It is usual not to notice if they stick as you can't see them revolving and cooking performance isn't badly impaired - they will however produce localised hot spots.

Replacing the stirrer fan blade and making sure it is free as well as replacing the top plastic cover will probably restore it to life.

The fire risk by the way is negligible. The plastic is self extinguishing and once power goes off the small amount of burning will soon stop.

Reply to
Peter Parry

Yes, I was aware of things causing issues like that and have no way of knowing if Mum left something else in there that caused such reflections.

Understood. This one has (had) a big glass turntable but I don't know if it also had the stirrer fan / rotating aerial (as mentioned later in the thread).

Basically it looks like there is a 'non metal' panel in the middle of the roof of the microwave and offset from the middle was a fairly clean round hole about the size of a 50p piece right through the plastic. The plastic food container Mum left in there accidentally (she keeps the (microwave use) food cover stacking tray and a couple of other things in there between uses) had some of the plastic from whatever fell out of the roof in it and the edges of the hole have some drippage, as would be typical of some thermo plastic that had hot very hot. There is also some smoke damage around the hole.

That is where we are I think Brian. The microwave went straight down the dump (daughter was going that way) so I'll not have chance to see what happened.

Yes, I don't think there was an actual risk of a fire because I think it was all over once the bit that melted actually melted.

That's cool.

Mum would need one with a very loud voice! ;-)

It's funny. She's never worked in an office or needed to use a typewriter but because her hearing isn't so good she can communicate easier with us by typing on the likes of MSN Messenger now Skype than she can on the phone. We just have to be patient re waiting for a reply. ;-)

Cheers, T i m

Reply to
T i m

Understood.

Seen.

Understood.

Interesting, thanks.

It did have a turntable if the two tend to be mutually exclusive?

Understood.

Understood. Mums oven had quite a large 'plastic' panel in the middle of the roof (150 x 100 possibly) whereas ours is a much smaller one (75 x 60).

Ignoring the fairly large hole that is now in the roof you mean. ;-)

Understood. I would have thought that was the case and I don't think Mum did anything in the way of extinguishing any flames and the 'damage' looked pretty localised.

If it wasn't for the fact it had a hole burned though, it being pretty old, it not been a 'microwave' and if I had more time to play with such things, I would have kept hold of it and taken it to bits to see if I could see how that particular one worked and what went wrong.

Cheers, T i m

Reply to
T i m

Overheat and catch fire. I had that at the weekend. About 3am I wanted a toasted cheese sandwich but the butter was in the fridge, I usally get it out cut a pit off put it on a saucer and microwave it for 109 seconds or so a few times until is's softened up a bit. But this time as there was only a bit left in the wrapper... It was anchor butter, I set the microwave to 90w (lowest setting) and about 15 seconds also the lowest setting, I set it off and ion under 5 mins there were flames fare larger than I'd expect from 1/10th of the normal size block of butter. I placed another saucer over the burning mound and then checked it all in the sink.

Reply to
whisky-dave

No, having both wasn't uncommon.

Reply to
Peter Parry

The transformers are well worth keeping if you fancy playing with lethal very high voltages (2 to 3 kV). Alternatively they can be turned into excellent spot welders.

Reply to
Peter Parry

'Normally' (before realising I don't have enough hours left in my life to do all the things I've got to do, let alone want or would like to do ...) I would have taken it to pieces and played with it all.

However, our daughter was there (and knowing the above) offered to take it away ...

Cheers, T i m

Reply to
T i m

It overheated because it has on/off cycling control, not proportional. AFAIK only Panasonic has proportional control these days and their reliability seems a bit iffy. That's why I have repaired our old Belling, because its LOW setting actually is.

Reply to
Capitol

Have you a link to a design for the welder?

Reply to
Capitol

The usual cause is food stuck on the plastic outlet cover.

All you need do to give it more life is remove the burnt cover. People are in such a rush to chuck away what they paid for.

Microwaves do cause fires, they're just less likely to than other cooker types, as they're more contained.

NT

Reply to
tabbypurr

Just rewind the transformer secondary with a few turns of welding flex. Be sure to keep the transformer thermal cutout in circuit. A mains switch is necessary, don't leave it on when not welding. Simple.

Compared to a standard 40A arc welder: They don't run long before overheating. less power less open circuit voltage makes them a bit harder to get the arc going.

Better is one where you put 2 MOTs in series on 240v, and the rewound secondaries in series. Less transformer heating, more power. Adding a fan that runs when the welder's not on cools quicker.

NT

Reply to
tabbypurr

Do a Google search for " microwave transformer spot welder" (without the quotes) will bring you pages of links and videos on the subject. Basically you cut off the high voltage winding and substitute two turns of large gauge copper wire. I used a piece of wire from an arc welder as the secondary winding. It must be flexible enough to fit around the transformer core. I first tried using a leftover length of meter tail wire (25mm2) but that was far too rigid. A local welding supplier found 2ft of arc welder lead of the same size but of hundreds of strands of wire making it much more flexible.

Reply to
Peter Parry

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