Re: Running an empty microwave oven

[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.

 

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

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

It dissipates. Where do you think the microwave transmitters on mountain
tops power ends up? It doesn't go round and round the earth forever.

 

[Fred McKenzie]

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

Peter-

If there is nothing in the microwave, there is no load, or at least very
little. If there is no load, there is no power dissipated. It is
somewhat like having 120 VAC at the wall socket with nothing plugged-in.

The problem isn't heat as much as voltage. With no load, the magnetron
voltage will be higher than normal. The question is really whether or
not damage will occur from over-voltage.

Someone in another thread a few weeks ago, said that only very early
microwave ovens would be damaged by running them empty. I know that one
I bought in 1976 came with a warning about running it empty, as well as
not putting anything metallic in it. However, two that were bought
about ten years ago did NOT come with such warnings, and even came with
metal racks!

Fred

 

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

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

Same question, where do the light waves go from the light inside the
microwave? Same energy, just higher frequency and lower power. Same
place as the microwaves.

 

[Bill Janssen]

Peter Hucker wrote:


break it?

overheating, or a build up of microwaves over a certain level?

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

into anything inside the oven. They are reflected completely by the metal
sides.

not completly, even if they were silver coated it would still not be quite
100%,
it bounces back and forth so quickly eventually even the smallest loss gets
multiplied suficiently to absorb considerable energy.

Colin =^.^=

While the microwave is bouncing around in the oven there will be
locations where the signal combines to generate
high voltages and other places where high currents are generated. These
locations can be in side of the Magnetron.

Bill K7NOM

 

[jasen]

Light is absorbed into all sorts of things. Microwaves are NOT absorbed
into anything inside the oven. They are reflected completely by the metal
sides.

that's not happening not unless those sides are superconductive

 

[PeterD]

well normally in order to cuase an explosion you have to have a combustable
material that burns very quickly,
the force comes from the fact that the burnt material wich is oxidesed takes
up a great deal more volume
and until it expands is under great pressure. in an empty oven there is no
combustables.

WEll, almost right... (and your 'normally' does apply, so what you say
is true, but there's more! <bg>)

All you need is pressure, not a combustable substance.

In the case of the balls that 'exploded' were they to have a 'strong'
outter shell, and a high moisture content inside, the moisture could
easily convert to steam and build up pressure until the outer shell
failed--an explosion... It would not be difficult to build up a
hundred PSI of steam pressure, and that would result in a rather large
'bang'!