Just FOUR days into 2026 – and I managed to blow up my microwave using potatoes

I am being completely serious about this, steam can be both powerful and dangerous in certain circumstances.

The expansion ratio for water into steam is 1,700 – that’s quite a lot.

Bear in mind, steam catapults are used to launch aircraft from carriers, and have to (in conjunction with the aircraft’s engines) get them up to flight speed in an extremely short distance.

All I had to was blow the door off my microwave oven 😲

While the side with the metal hinges was not affected, the side with the door latches was wrecked, and the plastic latch hooks were left inside the body when the expanding steam from the potatoes decided to make its bid for freedom.

If you’re not familiar with tinned, peeled potatoes, then you need to be aware that they behave like tiny steam powered bombs if not heated carefully. I decided to have a quick to prepare meal this evening, after spending longer than planned working in the cold outdoors, so dropped a few of these things in some boiling water (they’re already cooked), and set things up as usual, to heat them gently, to avoid the sort of explosive mess I learnt about years ago.

What went so dramatically wrong?

Normally, about five of these potatoes goes with whatever else I may be having.

However, the potatoes in tonight’s tin were TINY, meaning there were at least a dozen or more to be heated in the bowl.

Clearly, these came up to temperature MUCH faster than the usual larger examples, meaning the water inside began turning into steam sooner.

They don’t just release this steam, or gently vent it (the way a microwave baked potato does), but seem to trap it inside until they can’t hold it any longer – AND THEN THEY BLOW!

I think all but three exploded at the same time, creating enough pressure inside the oven to blow the door out, shearing the two door latches and leaving the hooks inside the body.

On a positive note, I discovered a new way to make mashed potato, something the microwave oven was filled with, as was the floor in front of the oven.

There’s more fun to come

I hadn’t noticed the latches had sheared – until I tried to close/latch the door and discovered it wouldn’t lock, then saw there were no latch hooks to be seen.

That ended that, as a microwave with no door latches or means to lock it closed is not even going to turn on.

Handily, I have a spare. Not used for years, this was added because it was also a conventional oven, and was used for items that wanted browning/grilling. Sadly, that didn’t last long. One of the radiant elements was poorly formed inside its silica tube, developed a hot spot, and burnt out. The ‘good news’ about that was that the manufacturer did not supply the elements as spare parts, leaving me with just the microwave part operational. I did try to fit some similar silica sleeved elements, but even those close to the right size developed hot spots as they could not be aligned perfectly, and always failed quickly.

I fired it up only to find it was apparently completely dead after sitting unused for years. Unlike the other microwave, which is analogue and infinitely variable, the newer one is digital, and the steps are TOO COARSE to allow fine power settings. I found it was either really slow compared to the ancient analogue unit, or too fast, leading to everything boiling over if I raised the power setting by just ONE step.

After trying to find out why the spare oven did not appear to be powering up…

I noticed EVERY electrical item in the kitchen was dead – it was actually in perfect working order once the breaker was reset.

When the door had been blown out of the old oven, and the latches sheared, this triggered one of the safety systems built into microwave ovens.

The two latches on the door act on two microswitches.

So long as the latches are in the correct positions, the microswitches do not connect anything.

HOWEVER, if the latches are NOT in the correct positions (which may indicate the door is not properly closed, so activating the magnetron to generate microwaves would be hazardous) the microswitch contacts are arranged to short the mains supply to the microwave, and blow the fuse immediately, ensuring it is not powered when the door is possibly not closed and latched correctly.

When the door was blown out, and the latches sheared, this created such a scenario, not blowing the fuse in this case, but tripping the (faster) breaker for the kitchen sockets.

And tomorrow’s job is…

I suppose I know what I’ll be doing tomorrow.

There are NO spares for my nice old analogue microwave – it’s just too old

I’ll have to fabricate new latches from scratch – no 3D printer here ☹

That should be all.

Oh well.

I was going to have to dig it out soon anyway, having noticed the turntable belt drive was occasionally juddering.

REVEALED! Riverside’s peculiar microwave oven

I’ve always been a little disappointed by the display of an early microwave oven in Riverside (Glasgow’s transport museum).

As seen in the pic below, it’s always on show with the lid closed, so it’s not possible to the interior, beneath the chrome.

That said, there’s no real mystery, as this type of microwave oven has been documented elsewhere, as summarised in the original post: Riverside’s peculiar microwave oven

Husqvarna Electronic Microwave Oven 1959

However, it’s always possible to ‘Do Better’, and my luck was in as was near Riverside recently, and popped in for a quick look.

Always surprisingly (or should I say disappointingly) busy, I’m grateful for my noise-cancelling earbuds, which help to tone down the sound of a thousand screaming kids which seems to fill the place nowadays.

Coming down the stairs at the back, I took a walk along the shop displays, and was rewarded with a view of this old microwave oven, in the OPEN position.

I’ve become slightly intrigued by this design, and wonder how effective it was.

A modern microwave oven has flat sides, and I’m guessing the dimensions of the aperture are designed to promote standing waves and resonance, to couple the maximum power from the magnetron, and avoid the waves just bouncing around in there and cancelling themselves out.

I’m not sure how this work using the shape seen here.

There’s an amusing episode of MythBusters from some years ago, where they thought they’d build a Mega Microwave, with FOUR magnetrons firing into the chamber.

As they built it, and fitted the magnetrons, I was surprised they didn’t take the operating frequency/wavelength into account, calculate the appropriate length, width, and height of the oven’s chamber, and position the magnetrons accordingly (for standing waves and reinforcement).

They were surprised, and mystified, when their Mega Oven not only didn’t work, and instantly incinerate anything placed inside, it didn’t work at all, and apparently didn’t produce ANY heating of the contents. This really was a surprise, as I’m usually impressed at their research, and level of attention paid to many of the myth they investigate and attempt to reproduce. In past episodes, they’ve often researched the reason for a failure, and revised their built to take that into account, but this time – nothing. They just scratched their heads, and were done with it.

I always wondered if there was ever a follow-up, or if anyone told them about their massive boo-boo.

Riverside’s peculiar microwave oven

Another pic I never used at the time I took it, this time from Riverside.

I’m not sure how many people visit museums and pay attention to displays that lie around the periphery, but it’s always worth taking a look at everything on offer. You never know what you might be missing.

In Riverside, the ground floor has a number of displays related to shops and services, with content ranging from toys, the cinema, garages, bike shops, and even pawnbroking.

Life was different in the past, and it wasn’t unusual to pawn items towards the end of a week, before the pay-packet was brought home by the breadwinner, and treasured possessions could be redeemed – until the end of the next week!

In Riverside’s pawn shop window there lies a very unusual item, one which most people will not recognise if they’ve only seen a present day version.

Looking distinctly modern for the day, and VERY science fictiony, is an early microwave oven.

It had me fooled the first time I saw it, mainly because I had been involved in high temperature testing, and for that we used shiny spherical electric furnaces to raise test subjects to over 1,000°C under tightly controlled conditions at their centre – this microwave oven looked very similar.

Husqvarna Electronic Microwave Oven 1959

Riverside’s description card for this device reads:

Husqvarna Microwave Oven Description

In the early 1950s, a microwave oven might have had a four-figure price tag, but by the end of that decade the price was dropping rapidly, and by the 1970s was around £200 and still falling quickly.

Before you start thinking that’s not so expensive, taking inflation into account, £200 in 1975 would be like £1,700 today.

There is some history of the microwave oven online, and it does date back to the 1945 thanks to the invention of the cavity magnetron, and a patent filed back then, for cooking, after an accidental discovery.

 Heating effect of a high-power microwave beam was discovered in 1945, completely by accident. Percy Spencer, who was a self-taught engineer from Howland, Maine and was an employee of Raytheon, worked on an active radar set when he noticed that a chocolate bar that he had in his pocket started to melt. He then tried an experiment with popcorn and then with an egg (which exploded). Spencer then created a high density electromagnetic field by feeding microwaves from a magnetron into a metal box from which they could not to escape. Temperature of a food placed in a box raised much faster that in open. Patent application for Spencer’s microwave cooking process was filed on October 8, 1945, by Raytheon and the first microwave oven was placed in Boston restaurant for testing. The first microwave oven usable by public was placed in Grand Central Terminal, in New York City, United States, in January 1947. It was in the form of the Speedy Weeny vending machine which dispensed hot dogs.

See History of Microwave Oven

There’s another one – in a Swedish museum

The delay in finally getting around to using this pic turned out to be fortunate.

First time around I tried to find more information about the Husqvarna microwave, with little success.

Incidentally, Husqvarna is a Swedish company founded in 1689 to produce muskets, and has grown considerably since then. It has diversified, and is now a brand name with multiple companies. Notably, it is a brand name for home appliances manufactured by Electrolux.

Second time around I must have used better phrasing, and came up with a later version, this one on display in the  Tekniska museet – Stockholm, Sweden, and shared in a Wikipedia media pic.

The description of the pic notes: “Cupol microwave oven, designed in 1969 by Carl-Arne Breger, Husqvarna, c. 1973“.

There’s also a small descriptive panel just visible at the bottom right of the oven, although the bottom is missing.

Swedish Cupol Description

Enlarged and translated, this says:

Microwave oven Cupol, Husqvarna This microwave oven is one of the first to be manufactured in Sweden. It was designed in 1969 by Carl-Ame Breger, who also designed the plastic packaging for the BigPack ice cream, the Rex children’s bicycle saddle and the Diavox phone. The microwave has…

Unfortunately, that’s all there is.

There’s no clue as to why there is a Mars bar sitting in the middle of the oven.

THAT’s going to make a bit of a mess if somebody turns the oven on.

Husqvarna Cupol Microwave Oven 1969

Despite a separation of some ten years between the two (if the information given is accurate), both items have a distinctly hand made appearance if looked at closely.

The labelling of the controls looks very ‘home-made’, and has more of the appearance of a prototype or design model than a production item intended for sale to the general public.

The figures on the example in Riverside don’t really match in terms of size and font, and the word ‘STOP’ is actually spelt as ‘STOPP’.

Both of these early examples appear to be missing one very important item now considered essential for a microwave oven…

Neither has a timer!