Running an empty microwave oven

[Peter Hucker]

Is it really true that turning on a microwave with nothing in it will break it?

Even more worrying - will it catch fire or explode?

Don't they have a safety cutout? Can't it sense the Klystron overheating, or a build up of microwaves over a certain level?

I have purchased a new microwave which has an easier to grab control. I'm concerned one of my pet parrots will switch it on! (Seriously, they do stuff like that)

--
http://www.petersparrots.com http://www.insanevideoclips.com http://www.petersphotos.com

A Pakistani arrives in London City all excited. He stops the first person he meets. "Good day, Mr. British, thank you to accept me in Your nice country", but the person interrupts and says: "I am not British, I'm Chinese."
The Pakistani continues on his way and meets another passer-by. "Thank you Mr. British for to let my family and me stay here... " Again, he's interrupted before finishing his sentence. "I no be British, I be Turk!"
He goes a little farther and meets another person and greets him "thank you for letting me come to your beautiful country." ... "I'm not British, I'm Kosavon."
"But," answers the Pakistani distressed, "where are the British??"
The Kosavon looks at his watch and says ..... "Probably at work."

 

[Jon Elson]

Is it really true that turning on a microwave with nothing in it will break it?

Even more worrying - will it catch fire or explode?

Don't they have a safety cutout? Can't it sense the Klystron overheating,

That would be a Magnetron tube, and yes, I thenk they all have a
thermostat on
the tube. This is also to prevent a fire if the cooling fan seizes up.
But, in the
case of no food to absorb the microwave energy, the reflected power can
build up
higher than normal voltages in the tube and cause permanent damage
before the
entire anode overheats.

or a build up of microwaves over a certain level?

I have purchased a new microwave which has an easier to grab control. I'm concerned one of my pet parrots will switch it on! (Seriously, they do stuff like that)

Parrots? What about kids? I suspect quite a few microwaves get "toasted"
by kids turning them on empty. I know they can survive a few seconds of
this abuse without noticeable damage. You could unplug it or leave the door
open (I'm pretty sure a parrot couldn't close the door.)

Jon

 

[Alison]

I have purchased a new microwave which has an easier to grab control. I'm

concerned one of my pet parrots will switch it on! (Seriously, they do
stuff like that)
Parrots. Cool

Leave a cup of water in it. Or something like those heat up aromatherapy
bags, the ones that have lots of little cherry stones in it.

 

[Peter Hucker]

concerned one of my pet parrots will switch it on! (Seriously, they do
stuff like that)

Parrots. Cool

13 of them. Messy. Noisy. But fun.

Leave a cup of water in it. Or something like those heat up aromatherapy
bags, the ones that have lots of little cherry stones in it.

That would only delay the problem. And I'd never remember to put a glass of water in after each time I use it.

I want to know what happens if it is switched on empty. The instructions just say it will damage it. That doesn't bother me too much, it was a very cheap one. As long as it doesn't explode or catch fire when I'm out of the house.

 

[Peter Hucker]

That would be a Magnetron tube, and yes, I thenk they all have a
thermostat on
the tube. This is also to prevent a fire if the cooling fan seizes up.
But, in the
case of no food to absorb the microwave energy, the reflected power can
build up
higher than normal voltages in the tube and cause permanent damage
before the
entire anode overheats.

So it'll just break? That's good to know. I don't want to lose a house or a parrot while out at work.

Parrots? What about kids? I suspect quite a few microwaves get "toasted"
by kids turning them on empty.

That's a point, it must happen a lot. If they caught fire or exploded, we'd see it on the news.

I know they can survive a few seconds of
this abuse without noticeable damage.

I once went for an interview at a company that makes magnetrons. As far as I know there is a thing that absorbs all returning microwaves. Wouldn't this just have a temperature sensor in it that would shut off the oven?

You could unplug it

The plug is behind the fridge. I used to plug it in above the worktop, but the parrots ate the plug!

or leave the door open (I'm pretty sure a parrot couldn't close the door.)

I bet it could, if it wanted to. But they are more interested in opening or breaking things. Parrots do not tidy or assemble things.

If I leave the door open, one will climb inside and chew up the cover that's over the magnetron output (it looks to be card).

 

[PeterD]

13 of them. Messy. Noisy. But fun.


That would only delay the problem. And I'd never remember to put a glass of water in after each time I use it.

I want to know what happens if it is switched on empty. The instructions just say it will damage it. That doesn't bother me too much, it was a very cheap one. As long as it doesn't explode or catch fire when I'm out of the house.

Look, the only safe thing is to unplug it. Even a glass of water won't
provide protection if they turn it on for 20 minutes! Use a short,
heavy duty (12 awg) extension cord, or some other similar device.

Either that, or make up a metal shield to cover the controls...

 

[Jon Elson]

So it'll just break? That's good to know. I don't want to lose a house or a parrot while out at work.

Well, if it has the safety thermostat on the anode, then it will
just shut down, probably forever. I have no idea whether the
safety thermostat is mandated by law or required by testing
agencies like UL, and whether the really cheap ones from China
have them. Without the safety stat, I don't know what would happen.

That's a point, it must happen a lot. If they caught fire or exploded, we'd see it on the news.

Well, I think there have been some fires from them, but probably
not a lot.

I once went for an interview at a company that makes magnetrons. As far as I know there is a thing that absorbs all returning microwaves. Wouldn't this just have a temperature sensor in it that would shut off the oven?

Not in an oven. Maybe in a radar transmitter, they have an
expensive part called a circulator that splits waves going in
different directions, and shunts returning waves to a terminating
resistor. Nothing like that in a microwave oven, believe me.

Jon

 

[colin]

Is it really true that turning on a microwave with nothing in it will break it?

Even more worrying - will it catch fire or explode?

Don't they have a safety cutout? Can't it sense the Klystron overheating,

or a build up of microwaves over a certain level?

I have purchased a new microwave which has an easier to grab control. I'm

concerned one of my pet parrots will switch it on! (Seriously, they do
stuff like that)

When I designed some of the early mcu controllers for them eons ago
we used to give them a heck of a lot of abuse such
as running them empty to try and get the mcu to crash,
(wich with a piggy back eprom mcu was all too easy)
ofc always a microwave leakage meter nearby,
the most spectacular thing was to melt the glass tray,
the turntable mechanism was the first thing to melt usually.

If theres food inside it will eventually catch fire and the flames will come
out of the back,
this was a serious liability worry at the time I assume theyve added some
safty things since I worked on them.

Some have water vapour detectors wich sense the peak and stop cooking, I
assume they will stop if nothing is detected.

Colin =^.^=

 

[Peter Hucker]

or a build up of microwaves over a certain level?
concerned one of my pet parrots will switch it on! (Seriously, they do
stuff like that)

When I designed some of the early mcu controllers for them eons ago
we used to give them a heck of a lot of abuse such
as running them empty to try and get the mcu to crash,
(wich with a piggy back eprom mcu was all too easy)
ofc always a microwave leakage meter nearby,
the most spectacular thing was to melt the glass tray,
the turntable mechanism was the first thing to melt usually.

If theres food inside it will eventually catch fire and the flames will come
out of the back,
this was a serious liability worry at the time I assume theyve added some
safty things since I worked on them.

Some have water vapour detectors wich sense the peak and stop cooking, I
assume they will stop if nothing is detected.

This is a £27 Tesco Value microwave - probably only has legal safety requirements.

I've already turned it on momentarily with nothing in it, as I'm used to an electronic one. If my food has gone cold due to a phonecall etc, I tend to shove it in and just turn the timer round to get it to go, then open the door after 20 seconds. The electronic ones cancelled the timer when you opened the door, but this one turns back on when you shut the door.

 

[Peter Hucker]

Look, the only safe thing is to unplug it. Even a glass of water won't
provide protection if they turn it on for 20 minutes! Use a short,
heavy duty (12 awg) extension cord, or some other similar device.

Nowhere is safe to plug it in without them chewing the plug. The plug has to be out of sight, which means I can't get to it to turn it off.

Either that, or make up a metal shield to cover the controls...

I bit of a hassle, and I'm useless at that kind of thing. And too lazy to do so unless I'm sure it would explode. Maybe I should buy another one and try it in the garden....

 

[colin]

This is a £27 Tesco Value microwave - probably only has legal safety requirements.

I've already turned it on momentarily with nothing in it, as I'm used to

an electronic one. If my food has gone cold due to a phonecall etc, I tend
to shove it in and just turn the timer round to get it to go, then open the
door after 20 seconds. The electronic ones cancelled the timer when you
opened the door, but this one turns back on when you shut the door.

Well, we used to leave them on for 24 hours soak test, if you put anything
in them it would be long incinerated by then,
so they were run empty,
they used to end up real hot but theres probably only about 600W of
microwave heating power plus losses ofc and theres a fan wich gets rid of
most of the heat so total temp rise is limited, the only real danger that I
can see is that it gets so hot the plastic/ferrite door seal melts,
this is serious becuase it is essential to form a safe seal from microwave
energy leaking past the door,
if the electronics gets too hot and melts it should safely blow the fuse and
so will no work again so should be safe.
if the magnetron blows up ofc this will probably also blow the fuse and end
up safe.
If the fan vent gets blocked this would probably make a meltdown more
certain.
ofc we did this in a building with little risk of any fire spreading.

but I assume theres a maximum limit on the timer ? polly would have to keep
setting it to max to cuase a problem I would think.
However this is by no means saying that it is safe, just that it is not
definatly going to be dangerous.
I wouldnt dare do that sort of thing these days lol.
I just hope your parrot doesnt learn how to open the door !

Colin =^.^=

 

[Geoff]

Is it really true that turning on a microwave with nothing in it will
break it?

Even more worrying - will it catch fire or explode?

Don't they have a safety cutout? Can't it sense the Klystron
overheating, or a build up of microwaves over a certain level?

I have purchased a new microwave which has an easier to grab control.
I'm concerned one of my pet parrots will switch it on! (Seriously,
they do stuff like that)

They will never reach the button, from inside.

CDs go really well in microwaves !

geoff

 

[Warren Weber]

Is it really true that turning on a microwave with nothing in it will
break it?

Even more worrying - will it catch fire or explode?

Don't they have a safety cutout? Can't it sense the Klystron overheating,
or a build up of microwaves over a certain level?

I have purchased a new microwave which has an easier to grab control. I'm
concerned one of my pet parrots will switch it on! (Seriously, they do
stuff like that)

Parrots are smart. One will go inside, next one could shut the door and turn
it on. Baked parrot for supper?

 

[Snap Whipcrack..............]

Is it really true that turning on a microwave with nothing in it will break it?

Even more worrying - will it catch fire or explode?

Don't they have a safety cutout? Can't it sense the Klystron overheating, or a build up of microwaves over a certain level?

I have purchased a new microwave which has an easier to grab control. I'm concerned one of my pet parrots will switch it on! (Seriously, they do stuff like that)

Microwave ovens don't care what you put inside. They do not have
feedback loops. You can cook a raisin or a melon or nothing at all.

 

[g]

Microwave ovens don't care what you put inside. They do not have
feedback loops. You can cook a raisin or a melon or nothing at all.

This isn't completely correct. A magnetron running into a perfectly
matched (lossy) load will see no reflected power. One operating into a
perfectly reactive load, an open or short for example, will see a large
reflected signal which will add to the forward wave. The result will be
higher voltage/current at the tube and a different operating point.

This is in fact a sort of feedback. It might be possible for the
tube or PS to fail due to excessive peak voltage or peak current. The
changed operating point might also cause more heat dissipation in the
tube or PS.

g

 

[Jon Elson]

This isn't completely correct. A magnetron running into a perfectly
matched (lossy) load will see no reflected power. One operating into a
perfectly reactive load, an open or short for example, will see a
large reflected signal which will add to the forward wave. The result
will be higher voltage/current at the tube and a different operating
point.

This is in fact a sort of feedback. It might be possible for the
tube or PS to fail due to excessive peak voltage or peak current. The
changed operating point might also cause more heat dissipation in the
tube or PS.

Assuming a true, perfect short at the end of the waveguide, then the
only dissipating
element left is the filament/cathode of the magnetron. Since there is
no real waveguide,
and the oven compartment is far from a perfect short, energy will be
dissipated in everything,
metal, plastic, glass, RF seals, etc.

Jon

 

[Peter Hucker]

an electronic one. If my food has gone cold due to a phonecall etc, I tend
to shove it in and just turn the timer round to get it to go, then open the
door after 20 seconds. The electronic ones cancelled the timer when you
opened the door, but this one turns back on when you shut the door.

Well, we used to leave them on for 24 hours soak test, if you put anything
in them it would be long incinerated by then,
so they were run empty,
they used to end up real hot but theres probably only about 600W of
microwave heating power plus losses ofc and theres a fan wich gets rid of
most of the heat so total temp rise is limited, the only real danger that I
can see is that it gets so hot the plastic/ferrite door seal melts,
this is serious becuase it is essential to form a safe seal from microwave
energy leaking past the door,
if the electronics gets too hot and melts it should safely blow the fuse and
so will no work again so should be safe.
if the magnetron blows up ofc this will probably also blow the fuse and end
up safe.
If the fan vent gets blocked this would probably make a meltdown more
certain.
ofc we did this in a building with little risk of any fire spreading.

Sounds reassuring. But does this also apply to cheap ones?

but I assume theres a maximum limit on the timer ? polly would have to keep
setting it to max to cuase a problem I would think.

Most likely they'd turn it slightly, about 5 minutes. When the thing turned on they'd probably get a fright and fly off anyway.

However this is by no means saying that it is safe, just that it is not
definatly going to be dangerous.
I wouldnt dare do that sort of thing these days lol.
I just hope your parrot doesnt learn how to open the door !

I can't see them opening the door. The like to twist and chew stuff. The door requires a hard pull (no button to push).

 

[Peter Hucker]

Parrots are smart. One will go inside, next one could shut the door and turn
it on. Baked parrot for supper?

As far as I know they're vegetarian.

 

[Peter Hucker]

Microwave ovens don't care what you put inside. They do not have
feedback loops. You can cook a raisin or a melon or nothing at all.

But where do you think the power ends up if it is not absorbed?

 

[Daniel Mandic]

Peter Hucker wrote:

(Seriously,

they do stuff like that)

Aha. My Cats like to turn on my Vaccuum cleaner and I get shocked, in
the first moments.

(Seriously, I have left the Vacuum cleaner connected to the wall-socket
many times, indeed. But it was never on, when I came back home)