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Author: Subject: combine two microwave ovens in to one furnace
rockyit98
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[*] posted on 23-9-2019 at 06:04
combine two microwave ovens in to one furnace


i got my hands on silicon carbide crucible 50ml .so my idea was to make microwave furnace since SiC is a good absorber. but only problem is i only got 2 of old 800W(out put power in put is 1100W) microwave ovens they are not that powerful .so i thought to combined the two because Inverter microwave ovens don't use a voltage stepper to double the voltage unlike conventional microwave ovens because of that voltage doubler oven only works half of the time . https://en.wikipedia.org/wiki/Voltage_doubler

BEN at Applied Science explain with details how conventional microwave ovens work. https://www.youtube.com/watch?v=I2k2g00onL0
https://en.wikipedia.org/wiki/Cavity_magnetron
watch TKOR https://www.youtube.com/watch?v=TVkioe3PJz0&list=PLbDYIZ...



i haven't don this before what are your thought

whirlpool-microwave-oven-wiring-diagrams-trusted-schematic-diagrams-whirlpool-microwave-parts-diagram.jpg - 107kB
WARNING and NOTE

microwaves are Dangerous specially up close they will pop your eyes up can get really bad burns.
HIGH VOLTAGE can kill you (4KV)
i am an experienced Electrical Mechanic .don't try this at home unless you are one too.

i,m leaving all the safety features intact like over heat protection .ect.
also more fan power to cool the magnetron and transformers .
the two ovens are 25L each. so i like to use 35L microwave oven casing and it's magnetron (1000w output) to so two transformer can fit together inside.
magnetrons have polarity also contain beryllium which is toxic with no cure https://en.wikipedia.org/wiki/Beryllium_poisoning .
ground the casing. control panel must handle the power i'm using analog microwave oven controller modified to handle 30A .
use cable and power socket that can power at least 3KW.
don't kill yourself


mv - Copy.jpg - 850kB

Attachment: Technical Guide Inverter microwave ovens.pdf (1.8MB)
This file has been downloaded 38 times
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Sulaiman
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[*] posted on 23-9-2019 at 06:51


If you are using two power supplies for one magnetron then I guess that the magnetron will overheat as it would be sized to just handle the power from one power supply.

As the crucible is small, why not just use one microwave oven as-is,
and surround the crucible with non-microwave-absorbing heat insulation ?




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rockyit98
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[*] posted on 23-9-2019 at 07:07


Quote: Originally posted by Sulaiman  
If you are using two power supplies for one magnetron then I guess that the magnetron will overheat as it would be sized to just handle the power from one power supply.

As the crucible is small, why not just use one microwave oven as-is,
and surround the crucible with non-microwave-absorbing heat insulation ?

Of course i'm gonna use insulation it can get very hot so hot that it probably can melt iron. as of cooling the magnetron i'm think in of separate fan that doesn't blow in to the cavity instead blow it outside.
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[*] posted on 23-9-2019 at 08:21


I know this isn't the purpose of this post, but would you mind explaining the mechanics of a microwave? I think this is as good a time as any to ask. Btw, neat idea!
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rockyit98
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[*] posted on 23-9-2019 at 08:32
How a Microwave Oven Works


Quote: Originally posted by Positively_Ionized  
I know this isn't the purpose of this post, but would you mind explaining the mechanics of a microwave? I think this is as good a time as any to ask. Btw, neat idea!

too lazy to google?
https://www.youtube.com/watch?v=kp33ZprO0Ck
Bill details how a microwave oven heats food. He describes how the microwave vacuum tube, called a magnetron, generates radio frequencies that cause the water in food to rotate back and forth. He shows the standing wave inside the oven, and notes how you can measure the wavelength with melted cheese. He concludes by describing how a magnetron generates radio waves.
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[*] posted on 23-9-2019 at 12:54


Actually magnetrons powered by doubler circuits only generate MW during the peak input voltage which is about 1/4 to 1/6 of the total time. As an other post has said that does not mean you can operate the magnetron at 4 to 6 times as much power.

Yes you can double the power output by operating the magnetron on a full wave supply but as an other poster has stated the magnetron will also have double the power dissipation which may damage it. The increased power dissipation could be mitigated by doubling the cooling air flow but there may be other difficulties such as over heating of the filament or the extra large dissipation in the magnetron when its driving unmatched load (empty oven or load that do not absorb the microwaves like water does).

I have a commercial microwave oven rated at up to 1,600W but it uses two magnetrons each with their own doubler circuit and separate wave guides to the oven enclosure.

The transforms have magnetic shunts between the primary and secondary winding which introduces induction in series with the secondary winding. That may be designed to limit the magnetron current and or in combination with the capacitor forms a shaping circuit that provides a flatter drive to the magnetron. The filament winding is also on the same side of the magnetic shunt as the HV which means the filament current is reduced as the magnetron HV current increases. Using two transformer in series and different capacitors would change that effect but I do not know how important those effects are.

I suggest you first try your silicon carbide crucible in a standared MO to see how hot it gets.

PS: there is no beryllium in domestic MO magnetrons.






i am wg48 but not on my usual pc hence the temp handle.

Thank goodness for Fleming and the fungi.
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rockyit98
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[*] posted on 23-9-2019 at 21:11


Quote: Originally posted by wg48temp9  
Actually magnetrons powered by doubler circuits only generate MW during the peak input voltage which is about 1/4 to 1/6 of the total time. As an other post has said that does not mean you can operate the magnetron at 4 to 6 times as much power.

Yes you can double the power output by operating the magnetron on a full wave supply but as an other poster has stated the magnetron will also have double the power dissipation which may damage it. The increased power dissipation could be mitigated by doubling the cooling air flow but there may be other difficulties such as over heating of the filament or the extra large dissipation in the magnetron when its driving unmatched load (empty oven or load that do not absorb the microwaves like water does).

I have a commercial microwave oven rated at up to 1,600W but it uses two magnetrons each with their own doubler circuit and separate wave guides to the oven enclosure.

The transforms have magnetic shunts between the primary and secondary winding which introduces induction in series with the secondary winding. That may be designed to limit the magnetron current and or in combination with the capacitor forms a shaping circuit that provides a flatter drive to the magnetron. The filament winding is also on the same side of the magnetic shunt as the HV which means the filament current is reduced as the magnetron HV current increases. Using two transformer in series and different capacitors would change that effect but I do not know how important those effects are.

I suggest you first try your silicon carbide crucible in a standared MO to see how hot it gets.

PS: there is no beryllium in domestic MO magnetrons.



hay thanks dude.you gave me a very good idea.since a magnetron only fire half of the time in a normal microwave .i could make the two of them then not fire at the same time.so one is working when other is not. can you tell me the model you have.

PS : beralium oxide is the pink ceramic use in the magnetron it is very good heat conductor only second to copper.you can test this by heating it with a lighter to test heat conductivity.
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[*] posted on 24-9-2019 at 01:22


this is my idea so two doesn't stay on at the same time.mind the winding diagram.

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[*] posted on 24-9-2019 at 02:04


Quote: Originally posted by rockyit98  
this is my idea so two doesn't stay on at the same time.mind the winding diagram.



Yes I think that a good idea and from my tests it would work.

I should add that on the one example of a double magnetron MO I have examined, the two magnetron's power supplies pulse at the same time as per the manual and the fact the transformers and connection were idenitical I checked that.

However each magnetron had its own wave guide connection to the oven with the long side of the wave guides at 90 deg to each other and mounted on the same wall of the oven. ie cross polarized. I think that reduces the amount of power that can reach a magnetron from the other magnetron .

I think I posted a pic of the the arrangement or the manual.

I found the thread http://www.sciencemadness.org/talk/viewthread.php?tid=64017#...

The wave guides exits were angle at only 30 deg to each other.

[Edited on 9/24/2019 by wg48temp9]




i am wg48 but not on my usual pc hence the temp handle.

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[*] posted on 24-9-2019 at 02:04


Why not wire two magnetrons as normal (diode cathode to ground)
and just reverse the connections to one of the transformer primaries ?




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[*] posted on 24-9-2019 at 02:26


Quote: Originally posted by Sulaiman  
Why not wire two magnetrons as normal (diode cathode to ground)
and just reverse the connections to one of the transformer primaries ?

that is what i did there .but when drawing a diagram it should be clear about polarity because two transformers are not from the same manufacturer.

Sad Samsung Twin Mag Commercial Microwave https://www.youtube.com/watch?v=7JagVT4Xexo


[Edited on 24-9-2019 by rockyit98]
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[*] posted on 24-9-2019 at 07:38


No, your diagram shows the phase of one of the secondaries reversed,
I am suggesting reversing the polarity of one of the primaries - much simpler.

By convention, it is assumed that coils are wound in the same direction
(because that is how coil winding machines are manufactured)
and the dot indicates the start of the winding.
For a multi-layer coil that means that the start of the winding (the end with a dot) will be nearer to the core than the other end.
In the case of microwave oven transformers, the inner end of the high voltage winding is also electrically connected to the core.
Reversing the phase of the secondary would require the connection to the core being removed,
and the inner windings would be at high voltage - risking arcing to the core.


An analogy in chemistry could be the difference between adding NaOH to water compared to adding water to NaOH




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[*] posted on 28-9-2019 at 05:00


Quote: Originally posted by rockyit98  


PS : beralium oxide is the pink ceramic use in the magnetron it is very good heat conductor only second to copper.you can test this by heating it with a lighter to test heat conductivity.


The pink ceramic is alumina containing chromium like these tig nozzels:
tignoz.jpg - 165kB

There is no technical reason why a domestic MO magnetron would need an expensive Beryllium oxide ceramic. It is true that some high power magnetrons use beryllium ceramic probably to isolate the cooling structure from the high voltage anode. Thats probably were the myth originated and then perpetuated by youtubers. There is an old thread that indicates the density of the pink ceramic is not consistent with it being beryllium and no domestic mangetron specs i have read warns of the dangers of the pink or white ceramic containing beryllium.




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[*] posted on 28-9-2019 at 11:27


Hnuh?

I had a buddy who used to utilize Beryllium Oxide and grease, to provide good heat-sink conduction, in prototype electronic devices. Not usual.

Causes me to run and wash my hands, every time I get "unknown composition" white grease on my hands, during oddball electronics disassembly.

Just in case. Beryllium is bad shit.

Standard use of Beryllium in domestic electronic devices, would be exceedingly reckless. But, such use, in military devices might be a possibility. Also, weird scientific equipment, and old stuff.
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