Maker Pro
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Microwave arcing

Our 5 year old Kenmore microwave has run perfectly with no abuse, no
metal used while cooking, etc. We have also used it to warm our plates,
and typically we warm one, two, or three dinner plates for between 1
and 2 minutes total. They always emerge nicely warmed, not hot but
just right. The plates are similar to what we'd call stoneware but not
as dense, perhaps some sort
of clay substance made by Pfaltzgraff. This shows the exact plate but
not the material, at http://www.pfaltzgraff.com/ca/13937.htm .

We have warmed plates in it for most of the 5 years since we discovered
this seems to work quite well. Today, while warming two plates, we got
a strong arc after only a second or two, which upon subsequent test
seems to occur behind the flexible white plastic square on the right
side
of the cavity (assume this is the magnetron horn?)

We shut it off immediately and then experimented further; it appears to
still function, warming a glass of water normally, warming a container
of rice normally, etc. However, placing the plates back in causes an
almost immediate arc.

So, what's changed? Have the plates somehow become more/less load now
(unlikely; we tried two other plates as well with the same result.)

I'm guessing maybe a buildup of grease or residue in the magnetron area
may have changed it's parameters somehow, to the extent that it's no
longer 'happy' being asked to warm plates.

Ideas? (Other than "don't do that" please...)
 
I

ian field

Jan 1, 1970
0
Our 5 year old Kenmore microwave has run perfectly with no abuse, no
metal used while cooking, etc. We have also used it to warm our plates,
and typically we warm one, two, or three dinner plates for between 1
and 2 minutes total. They always emerge nicely warmed, not hot but
just right. The plates are similar to what we'd call stoneware but not
as dense, perhaps some sort
of clay substance made by Pfaltzgraff. This shows the exact plate but
not the material, at http://www.pfaltzgraff.com/ca/13937.htm .

We have warmed plates in it for most of the 5 years since we discovered
this seems to work quite well. Today, while warming two plates, we got
a strong arc after only a second or two, which upon subsequent test
seems to occur behind the flexible white plastic square on the right
side
of the cavity (assume this is the magnetron horn?)

We shut it off immediately and then experimented further; it appears to
still function, warming a glass of water normally, warming a container
of rice normally, etc. However, placing the plates back in causes an
almost immediate arc.

So, what's changed? Have the plates somehow become more/less load now
(unlikely; we tried two other plates as well with the same result.)

I'm guessing maybe a buildup of grease or residue in the magnetron area
may have changed it's parameters somehow, to the extent that it's no
longer 'happy' being asked to warm plates.

Ideas? (Other than "don't do that" please...)

Just remove the plastic bit, but make sure not to put food in there that can
"burst" and splatter into the waveguide.
 
There is probably a build-up of carbonized food on the back side of the
plastic plate. Do as the previous poster said. You may or may not be
able to clean the plastic sufficiently to put it back. The potential
for arcing has always been there, it is just that the food build-up
finallly broke down under the high fields that occur when the oven
cavity is lightly loaded. That is why you are always cautioned not to
run the microwave under no-load conditions which is about what you are
doing when you just pout loates in there. You can still warm plates,
just put some water in a container in the microwave at the same time.
The water will absorb much of the energy and it will take you longer to
heat the plates. Why not just run them under hot water for a few
seconds?

H. R. (Bob) Hofmann
 
N

nucleus

Jan 1, 1970
0
does your operating manual suggest using a microwave oven to heat
plates?

a microwave oven is designed to heat items containing water. a water
molecule is composed of a single atom of oxygen with two atoms of
hydrogen attached at a specific angle to the oxygen atom. the
frequency
of a microwave oven is designed to cause the hydrogen atoms to
vibrate, causing friction with adjacent water molecules, thereby
generating heat.

clays contain minerals rich in metal oxides. the metal in your plates
possibly has been marginal in the past and due to usage, the addition
of molecular metal particles from flatware may have caused the change.
 
I think you nailed it, Bob... there were a couple of blobs of stuff on
the backside of the shield; easy enough to clean up with some steel
wool and then I remounted on the reverse so the waveguide shoots
through a different area of the material. Seems to clear up the
problem.
Running hot water might be an option but not nearly as convenient as
just popping them in the micro.

Thanks.
 
L

Lee

Jan 1, 1970
0
I think you nailed it, Bob... there were a couple of blobs of stuff on
the backside of the shield; easy enough to clean up with some steel
wool and then I remounted on the reverse so the waveguide shoots
through a different area of the material. Seems to clear up the
problem.
Running hot water might be an option but not nearly as convenient as
just popping them in the micro.

Thanks.
If you checked your manual, you would find that shield is NOT to be
cleaned with anything abrasive. It is made of a compound that is part
of the distribution of the microwaves.
My first unit manual said that (early 80's) and the one I bought a week
ago also said that as well.
My first unit was a Sharp, ($1,200) and included a 9 hour cooking course
with it. The very first night, they had a Sharp tech there that said
any dish that contained clay was not to be used as there is always trace
amounts of metals in clay. He also said that if any container that got
hot in the machine when there was no food/water, should not be used.
Why don't you email the manufacturer of the plates and ask if they are
microwave safe. I'll lay odds the answer is NO.
Regards
Lee in Toronto
 
Our 5 year old Kenmore microwave has run perfectly with no abuse, no
metal used while cooking, etc. We have also used it to warm our plates,
and typically we warm one, two, or three dinner plates for between 1
and 2 minutes total. They always emerge nicely warmed, not hot but
just right. The plates are similar to what we'd call stoneware but not
as dense, perhaps some sort
of clay substance made by Pfaltzgraff. This shows the exact plate but
not the material, at http://www.pfaltzgraff.com/ca/13937.htm .

We have warmed plates in it for most of the 5 years since we discovered
this seems to work quite well. Today, while warming two plates, we got
a strong arc after only a second or two, which upon subsequent test
seems to occur behind the flexible white plastic square on the right
side
of the cavity (assume this is the magnetron horn?)

We shut it off immediately and then experimented further; it appears to
still function, warming a glass of water normally, warming a container
of rice normally, etc. However, placing the plates back in causes an
almost immediate arc.

So, what's changed? Have the plates somehow become more/less load now
(unlikely; we tried two other plates as well with the same result.)

I'm guessing maybe a buildup of grease or residue in the magnetron area
may have changed it's parameters somehow, to the extent that it's no
longer 'happy' being asked to warm plates.

Ideas? (Other than "don't do that" please...)

dont do that, put a cup of water on the plates when you nuke them.

Keep the plastic bit clean to prevent this recurring.

Dont run the machine with the plastic waveguide cover removed, as food
splatters will enter the waveguide, this will short out, and cleaning
it out will then be difficult or impossible.


NT
 
S

Sam Goldwasser

Jan 1, 1970
0
Lee said:
If you checked your manual, you would find that shield is NOT to be
cleaned with anything abrasive. It is made of a compound that is part
of the distribution of the microwaves.
My first unit manual said that (early 80's) and the one I bought a week
ago also said that as well.

They don't want you to destroy it but it is just a piece of plastic that
is transparent to microwaves.
My first unit was a Sharp, ($1,200) and included a 9 hour cooking course
with it. The very first night, they had a Sharp tech there that said
any dish that contained clay was not to be used as there is always trace
amounts of metals in clay. He also said that if any container that got
hot in the machine when there was no food/water, should not be used.
Why don't you email the manufacturer of the plates and ask if they are
microwave safe. I'll lay odds the answer is NO.

He's been doing it for years without incident. So, something else has
changed. As long as the plates absorb some of the energy, it won't hurt
the oven. That's the same thing a glass of water does.

I'd guess there is some burnt on crud which is causing the arcing.

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I

ian field

Jan 1, 1970
0
nucleus said:
does your operating manual suggest using a microwave oven to heat
plates?

a microwave oven is designed to heat items containing water. a water
molecule is composed of a single atom of oxygen with two atoms of
hydrogen attached at a specific angle to the oxygen atom. the
frequency
of a microwave oven is designed to cause the hydrogen atoms to
vibrate, causing friction with adjacent water molecules, thereby
generating heat.

clays contain minerals rich in metal oxides. the metal in your plates
possibly has been marginal in the past and due to usage, the addition
of molecular metal particles from flatware may have caused the change.

You should see the items Braniac (science abuse) TV show puts in the
microwave - on average about half the items result in the steel casing being
unfolded back to sheets of steel! Some of the less destructive items at
least provide an entertaining light show.
 
nucleus said:
does your operating manual suggest using a microwave oven to heat
plates?

a microwave oven is designed to heat items containing water. a water
molecule is composed of a single atom of oxygen with two atoms of
hydrogen attached at a specific angle to the oxygen atom. the
frequency
of a microwave oven is designed to cause the hydrogen atoms to
vibrate, causing friction with adjacent water molecules, thereby
generating heat.

clays contain minerals rich in metal oxides. the metal in your plates
possibly has been marginal in the past and due to usage, the addition
of molecular metal particles from flatware may have caused the change.

Nukes are nothing like that fragile. You can heat plates in them, melt
aluminium & iron in them, or put metal foil on food in them. The
problem is just lack of load, the plates dont absorb much, plus burnt
muck on the waveguide entry cover.

Contrary to myth, magnetrons are not killed by running them with no
load, that only applied to the very first commercial microwave oven
iirc. However it does tend to cause arcing, and that can do minor
damage in the cooking cavity, the worst example of which is frying that
plastic plate. Once theres carbon on that, it will deteriorate until it
catches fire. So keep that lil cover clean.


NT
 
nucleus said:
does your operating manual suggest using a microwave oven to heat
plates?

a microwave oven is designed to heat items containing water. a water
molecule is composed of a single atom of oxygen with two atoms of
hydrogen attached at a specific angle to the oxygen atom. the
frequency
of a microwave oven is designed to cause the hydrogen atoms to
vibrate, causing friction with adjacent water molecules, thereby
generating heat.

clays contain minerals rich in metal oxides. the metal in your plates
possibly has been marginal in the past and due to usage, the addition
of molecular metal particles from flatware may have caused the change.

Nukes are nothing like that fragile. You can heat plates in them, melt
aluminium & iron in them, or put metal foil on food in them. The
problem is just lack of load, the plates dont absorb much, plus burnt
muck on the waveguide entry cover.

Contrary to myth, magnetrons are not killed by running them with no
load, that only applied to the very first commercial microwave oven
iirc. However it does tend to cause arcing, and that can do minor
damage in the cooking cavity, the worst example of which is frying that
plastic plate. Once theres carbon on that, it will deteriorate until it
catches fire. So keep that lil cover clean and you can cast iron in it
in peace.


NT
 
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