EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: German_EE on June 18, 2017, 04:12:23 pm
-
Anybody want to stand in front of this microwave?
https://i.chzbgr.com/full/4165340672/
Image is safe for work but may cause a sharp intake of breath if you know how dangerous it is.
-
I know metal is bad in microwaves, but I am not sure what would happen here. Would it act as a microwave antenna or something else?
-
It would also need all the interlocks disabled to work... or is it covering a damaged door? Looks like the foil is wrapping around the original door edges.
In that case it might be sort of OK provided there is proper microwave absorbing material (such as food) in the cavity I guess.
The gap around the door would be below cutoff assuming the foil wraps around it to the backside on all four edges and, if the front window was broken but the steel mesh was still there, the foil could/should/might be effective too.
Another issue is if the door front was damaged it might be warped and the gap around it might not be small enough to block all RF leakage.
You "might" be able to make this work if you have an RF survey meter but why....
But still :palm:
-
But WHY does it have alfoil wrapped over the original door?
Is the door underneath modified? Maybe the glass broke?
If it's just the glass missing, then there is no problem since the EM shielding in the door is provided by the metal mesh, that has the door edge EM-seal fingers integral with the mesh.
Probably the foil is just due to someone being ignorant and thinking that if they can see the food, there must be evil microwaves leaking out. Or they broke the glass, leading to the same incorrect assumption.
The only real risk is that if they continued the foil around to the mating face of the door, the uneven thicknesses of the scrunched-up foil are probably diminishing the effectiveness of the RF seal there.
Simple way to tell - measure with a cheap microwave leakage detector.
-
But WHY does it have alfoil wrapped over the original door?
Is the door underneath modified? Maybe the glass broke?
If it's just the glass missing, then there is no problem since the EM shielding in the door is provided by the metal mesh, that has the door edge EM-seal fingers integral with the mesh.
Probably the foil is just due to someone being ignorant and thinking that if they can see the food, there must be evil microwaves leaking out. Or they broke the glass, leading to the same incorrect assumption.
The only real risk is that if they continued the foil around to the mating face of the door, the uneven thicknesses of the scrunched-up foil are probably diminishing the effectiveness of the RF seal there.
Simple way to tell - measure with a cheap microwave leakage detector.
These were my thoughts, too. ^ ^ ^
As for the foil wrapping around the edge of the door, I would think the foil would compress pretty well ... enough for me to not be too worried - that is, if the mesh on the door mesh was intact.
If not .... then I'd be a little anxious.
-
I reserve the word "beyond scary" to kreosan's videos.
Umm, yes, wow. I just searched for that.. I cringed as soon as the magnetron came out, and didn't stop until the video ended :scared: :-DD
Thanks for the intro to his channel :)
Ash.
-
Anybody want to stand in front of this microwave?
https://i.chzbgr.com/full/4165340672/
Image is safe for work but may cause a sharp intake of breath if you know how dangerous it is.
That'd probably be safer than standing beside it! :o
-Pat
-
I know metal is bad in microwaves, but I am not sure what would happen here. Would it act as a microwave antenna or something else?
Well, kind of. Metal in microwaves is perfectly acceptable, it just needs to be done correctly.
Metal (including thin sheets of aluminium foil) reflect the 2.4GHz inside the microwave cavity which can be useful for preventing certain parts cooking too quickly, such as thinner areas of an otherwise fairly thick piece of meat.
Straight from the operating instructions of my (Sharp) microwave oven: Contrary to popular belief, foil can be used in the microwave – for shielding, not covering. It must not come in contact with the walls of the microwave. Some of the recipes in the back of the book also include the use of foil.
-
So then, what is the issue here? Knowledge in electronics doesn't equate to knowledge in the specialty field of microwave engineering and the OP seems to assumes that knowledge is universal.
-
I think here someone tries to be clever. See, there is a metal mesh on the door, you can see through it. So the microwaves can come out of it. You know, in the small holes. Since aluminum (sic!) stops government thought control rays, and there is no such thing as mu metal in the periodic table, its gotta work.
-
A fine prank in school was to flip around the contacts on the door switch off the microwave from the normally opened to normally closed in rival student houses. So the microwave would refuse to work with the door closed but would work with the door opened. Rumor was seeing how people worked around it was a good way to tell what major they should be..
The standard joke was something like the EE would switch the contacts back, the physicist would decide where to stand to minimize exposure, the chemist would wrap the whole thing in aluminum foil and the mathematician would go through the motions of using the non functional microwave and eat their burrito cold without noticing. I forget the exact wording.
In practice people knew the prank and were mildly annoyed or amused depending on their mood.
-
As well as being stupid and dangerous I would be very surprised if you could flip around a pair of contacts to make a microwave work with the door open. The timing of the opening and closing of the primary interlock switch, monitor switch and secondary interlock switch is a safety feature and the switches must be aligned so that they operate in the correct order otherwise you would blow mains fuses, which is the whole purpose. As far as I know the interlock switches have normally closed closed and do NOT have a normally open contact.
-
All I know is someone did it to the microwaves in our house one summer (or the microwaves had a really bad failure mode that hit more than one at once). Note I didn't see the rewiring, so it is possible the NO/NC switcharoo was the simplistic explanation given. But i did get to witness the effects when trying to make late night popcorn. The microwave had a mechanical timer with a real knob I remember. Darn rudds (or was it pageboys?) Rewired our microwaves again. Time to retaliate. A false flag operation was not out of the question.
-
To be honest I've never seen any microwave interlock switches with a separate normally closed switch. Had an oven that would blow fuses every time you opened the door and that was due to wear on the switches and actuators so the monitor interlock was closing before the primary interlock opened, it was cheaper to buy a new oven than a set of interlocks.
-
It's to protect your nuts, because nobody likes roasted nuts. :-DD
-
It's to protect your nuts, because nobody likes roasted nuts. :-DD
I like roasted nuts out of the jar, not out of my pants.
-
As well as being stupid and dangerous I would be very surprised if you could flip around a pair of contacts to make a microwave work with the door open. The timing of the opening and closing of the primary interlock switch, monitor switch and secondary interlock switch is a safety feature and the switches must be aligned so that they operate in the correct order otherwise you would blow mains fuses, which is the whole purpose. As far as I know the interlock switches have normally closed closed and do NOT have a normally open contact.
The last one I repaired used a couple of standard SPDT microswitches in series for the interlock - one of them had failed open. There was certainly no fancy sequencing. It was a nice inverter oven too.
-
As well as being stupid and dangerous I would be very surprised if you could flip around a pair of contacts to make a microwave work with the door open. The timing of the opening and closing of the primary interlock switch, monitor switch and secondary interlock switch is a safety feature and the switches must be aligned so that they operate in the correct order otherwise you would blow mains fuses, which is the whole purpose. As far as I know the interlock switches have normally closed closed and do NOT have a normally open contact.
The last one I repaired used a couple of standard SPDT microswitches in series for the interlock - one of them had failed open. There was certainly no fancy sequencing. It was a nice inverter oven too.
Perhaps safety standards for household appliances are less strick in the US than Europe?
-
On a 2.4 GHz microwave oven, the door has a 1/4 wave shorted slot formed into its depth; the out of phase reflection cancels leakage which would otherwise pass through the slot antenna formed where the door meets the chassis. On the old 900 MHz microwave ovens, a 1/4 wave slot in the door would have been too large so instead conductive finger stock is used to seal the cavity; unfortunately the exposed finger stock is subject to damage, food getting on it, etc. so these ovens fell out of favor which is unfortunate since they cooked food more evenly.
As far as the aluminum foil shown, I think someone is being paranoid.
-
On a 2.4 GHz microwave oven, the door has a 1/4 wave shorted slot formed into its depth; the out of phase reflection cancels leakage which would otherwise pass through the slot antenna formed where the door meets the chassis. ... As far as the aluminum foil shown, I think someone is being paranoid.
There's a potential problem - what if the foil wraps around the door so that it covers the 1/4 wave slot?
-
On a 2.4 GHz microwave oven, the door has a 1/4 wave shorted slot formed into its depth; the out of phase reflection cancels leakage which would otherwise pass through the slot antenna formed where the door meets the chassis. ... As far as the aluminum foil shown, I think someone is being paranoid.
There's a potential problem - what if the foil wraps around the door so that it covers the 1/4 wave slot?
The photograph does show that, doesn't it? Then the 1/4 wave shorted slot would not work and the door would leak like mad.