Re: Running an empty microwave oven

Discussion in 'Beginner Electronics' started by Snap Whipcrack.............., Jan 23, 2007.

  1. Peter Hucker wrote:
    > 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.............., Jan 23, 2007
    #1
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  2. Peter Hucker wrote:
    > On Tue, 23 Jan 2007 16:49:43 -0000, Snap Whipcrack.............. <> wrote:
    >
    >> Peter Hucker wrote:
    >>> 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.

    >
    > 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.
    Snap Whipcrack.............., Jan 24, 2007
    #2
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  3. In article <op.tmmhywbk4buhsv@fx62>, "Peter Hucker" <>
    wrote:

    > On Tue, 23 Jan 2007 16:49:43 -0000, Snap Whipcrack..............
    > <> wrote:
    > > 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?


    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
    Fred McKenzie, Jan 25, 2007
    #3
  4. Peter Hucker wrote:
    > On Tue, 23 Jan 2007 16:49:43 -0000, Snap Whipcrack.............. <> wrote:
    >
    >> Peter Hucker wrote:
    >>> 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.

    >
    > 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.
    Snap Whipcrack.............., Jan 28, 2007
    #4
  5. Snap Whipcrack..............

    Bill Janssen Guest

    colin wrote:
    > "Peter Hucker" <> wrote in message
    > news:eek:p.tmvmmskc4buhsv@fx62...
    >
    >> On Sun, 28 Jan 2007 15:35:16 -0000, Snap Whipcrack..............
    >>

    > <> wrote:
    >
    >>> Peter Hucker wrote:
    >>>
    >>>> On Tue, 23 Jan 2007 16:49:43 -0000, Snap Whipcrack..............
    >>>>

    > <> wrote:
    >
    >>>>> Peter Hucker wrote:
    >>>>>
    >>>>>> 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.
    >>>>>
    >>>> 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.
    >>>

    >> 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.
    >
    > 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
    Bill Janssen, Jan 29, 2007
    #5
  6. Snap Whipcrack..............

    jasen Guest

    On 2007-01-28, Peter Hucker <> wrote:
    >
    > 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

    --

    Bye.
    Jasen
    jasen, Jan 29, 2007
    #6
  7. Snap Whipcrack..............

    PeterD Guest

    On Thu, 01 Feb 2007 12:58:14 GMT, "colin"
    <> wrote:

    >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'!
    PeterD, Feb 1, 2007
    #7
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