RogueRose
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"Hacked/Modified" Microwave to 2-3x power (4,000 watts) - thoughts?
I've taken apart a number of microwaves and it would be fairly easy to modify one to add 1 or 2 additional magnetrons to increase the power. The
electronics and physical properties of it is pretty sound, I would probably take 2-3 identical units to make the single unit and build a larger "oven
box" to allow larger items to fit in. It would probably need 240v and could draw up to about 4500 watts.
I'm wondering how often microwaves are used in a lab setting (chemistry related) but I know that I use it for other things where the high power would
be of significant benefit. I found a 3200 watt for almost $4000.
The only question I have is whether opposing magnetrons would cancel out the opposing output.
So, would something like this be useful in a lab setting? Just imagine making a hotdog in 10 seconds!
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Mesa
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The circuit breakers on a standard residential powerbox are 2400watt. You wouldn't be able to power it unless you ran it off 2 separate lines.
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deltaH
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If they're out of phase, won't they overheat?
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battoussai114
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If you use outlets that come from the same line the breaker switch is going to overheat and cut the power out. You'd need to use a different
distribution line for each additional magnetron or have a high power line on your shop.
And remember that it's important to keep the structural integrity of the metal shell of the MW oven since it's them acting as a Faraday cage that keep
radiation from leaking.
Batoussai.
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Little_Ghost_again
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The transformers will squeal if you try and over saturate the core
Dont ask me, I only know enough to be dangerous
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Upsilon
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Quote: Originally posted by Mesa  | | The circuit breakers on a standard residential powerbox are 2400watt. You wouldn't be able to power it unless you ran it off 2 separate lines.
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Many homes (like mine) have a 50 amp recepticle which you can draw 6000W from.
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aga
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The main problems would be the Phase and Frequency matching to get the extra magnetrons to Add power instead of reducing or cancelling.
It would be very hard to match them exactly, so assuming 1000W x 2 = 2000W of heating would be extremly optimisitic.
The ryder to that is that it would also be unlikely to match them anti-phase 100% so you'd not get 0W either.
Another approach would be to hit the target from different angles from each magnetron, so at least some % of energy from each is absorbed by the stuff
you want to heat before wave interaction happens.
I.e. get the energy from each magnetron into the Target rather than try to combine them to make a single more powerful beam.
Remember that the magnetron is not 100% efficient, so to get X Watts you'll need to look up the overall system efficiency and increase the expected
current draw from your mains electricity accordingly.
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Dr.Bob
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Just get a macrowave instead! :-)
Most of the commercial lab microwaves are designed for small samples, thus even 300 watts works fine to heat up a 1-30 ml sample to 200+ C. The two
brands of larger ones are built with more custom magnetrons so they have more power from one source, but very regulated and controllable, thus the
price.
Unless you are aiming to boil off large amounts of water, just heating a sample in even a simple home microwave will work pretty well, but if you are
planning to boil off large amounts of water, the energy needed will quickly be too much. In that case, it is much simpler to just use a commercial
boiler or natural gas heat source as they can generate more steam than any normal microwave. But they do use large industrial microwaves to heat
plywood and laminated beams as they can heat the wood quickly without burning it.
If you wanted to do multiple magnetrons, the orthogonal idea is best, on on each axis, X, Y, and Z. They will still cancel out some, but less than
most other configurations, I would think. And if you have a stove or clothes drier outlet you can get 220 and/or high amperage, but more risk of
fire or shock if you mis-design you macrowave. Good luck.
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m1tanker78
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The waveguide(s) must be kept intact. The inner chamber (where you put the food) is essentially a resonant cavity. With that in mind and barring
extreme modification of the resonant cavity, firing 3 electron beams into the cavity would produce erratic results at best IMO. Even if the 3 MOTs are
operating on the same phase, what a mess..
I suppose a resonant cavity can be built that has a summing effect (minus RF/thermal losses). Coupling the stages would be tricky but not impossible.
Sounds like a fun thought exercise. Maybe someone here has worked with high power RF transmitters and can offer some food for thought?
Chemical CURIOSITY KILLED THE CATalyst.
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RogueRose
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Any power issue or breaker issue would be dealt with prior to testing.
What I was planning on doing was running X number of magnetrons, each with own breaker/circuit (each is a 1500w magnetron) but they will be controlled
by a single microwave which will tun the magnetrons on and off, spin the carousol, run convection fan, etc.
I saw a 4500w MW and it was like $11,500!!!
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TheIdeanator
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You could tap into the 240V for the stove and wire the transformers in series which might be the most bulletproof way to go. You'd need to adjust the
timers and relays and such and I can't speak to how well the chamber would react.
If you can't tap that, you'll need to find out if the outlets you'd like to use are in phase with each other. You could probe the two hots in the
breaker box to see if they're 0V (in phase) or 220V (out of phase) to each other. You could either rewire the box or find an outlet set that works.
Actually, it probably wouldn't matter, just swap the hots and neutrals around so all are in-phase.
Microwave chambers have always seemed like pretty basic boxes and should be simple to design. I imagine the distance between the magnetron and the far
wall of the chamber is an n/2 multiple of the wavelength, I wouldn't be surprised all internal dimensions are probably like that. If you want to build
a bigger box to accommodate the extra magnetrons neatly, that's the first thing I'd look into. I can't be arsed to research that at all so take it as
you will.
Also: damn you! You made me remember the magnetron furnace I wanted to build at one point and I was wondering about how to acquire a 1700C+ electric
furnace to refine berylium.
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Praxichys
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It won't work. The antenna on one magnetron will receive the microwaves from the other and it will overheat. You cannot phase match the magnetrons
because the resonant cavity is not a constant. The load in the cavity changes with whatever is inside and there is a mode stirrer to make sure the
resonant cavity is not consistently resonant, to prevent cold and hot spots. You need a single, more powerful magnetron that can handle its own
reflected power, otherwise each magnetron will need to be able to receive at peak the sum of the power from all other magnetrons involved.
Phase matching the power supplies is useless. The magnetron uses a high voltage DC supply and a series of resonant cavities to
generate a 2.45 GHz resonation. Slight variations in internal architecture will delay the onset of this from one to the other. You will never get them
to lock phase.
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franklyn
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Your basic HERF gun.
If this is only to be used for heating , the energy emitted by each magnetron will add together. Energy reflected
back to the emitters will tend to move the entire arrangement into resonance. With the separate magnetrons operating in phase you have a ' phased
array ', in effect something like a maser. The emitters should be arranged at right angles or parallel , not opposed as that will tend to contain the
energy rather than distribute it.
Three arranged on a box corner , one on each plane should work best.
www.engadget.com/2006/10/23/inventors-claim-to-turn-300-micr...
www.newscientist.com/article/dn10356-invention-microwave-ove...
www.freepatentsonline.com/20060208672.pdf
www.google.com/patents/US20060208672
www.google.com/patents/US7164234
www.tpub.com/neets/book11/45i.htm
http://repairfaq.cis.upenn.edu/REPAIR/F_micfaq6.html
http://cdn.preterhuman.net/texts/government_information/inte...
Unlike other physical waves electromagnetic energy outside of wires does not add or subtract.
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Praxichys
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Uhh... explain laser interference patterns then. If EM couldn't con/destructively interfere, interferometers would be... not invented?
Also, what you mean to do by mounting them at right angles is to isolate them based on phase polarization. Polarization is changed with reflection, so
while it might work for a HERF gun which has essentially zero reflected power, it will destroy the magnetrons if used in a microwave oven.
[Edited on 10-11-2015 by Praxichys]
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franklyn
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@ Praxichys
I don't really know why I should , you're so hopelessly uninformed this is over your head.
What I said is there is no change in the energy magnitude , photons do not combine into bigger photons.
Interference is a Moire pattern. Just as a shear wave pattern may appear to exceed the speed of light. It's merely a geometric pattern much as an
optical illusion where separate pieces of a chair when viewed at a specific perspective gives the illusion of being a chair.
The emitters can act as antennas receiving some energy back which generates a current that alters that which is running in each magnetron itself. This
is similar to the feedback that provides reinforcement in an oscillator.
www.allaboutcircuits.com/textbook/semiconductors/chpt-8/posi...
www.sciencemadness.org/talk/viewthread.php?tid=9129#pid10554...
www.sciencemadness.org/talk/viewthread.php?tid=22619#pid2689...
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phlogiston
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It may be possible to lock the magnetrons using PLL techniques, but it is probably a huge amount of work. If all you intend to do with it is to heat
something, there are easier methods.
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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zed
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The question is..."Do you need all of that power, for some special reason?"
Many people have reported good chemistry results with ordinary home microwave ovens.
You can shove a big V8 engine, into an old VW Bug, but do you really need to?
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TheIdeanator
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| Quote: Originally posted by Praxichys | | It won't work. The antenna on one magnetron will receive the microwaves from the other and it will overheat. You cannot phase match the magnetrons
because the resonant cavity is not a constant. |
That crossed my mind and I was hoping that the differences would be so slight as to be a negligible problem.
| Quote: Originally posted by phlogiston | | It may be possible to lock the magnetrons using PLL techniques, but it is probably a huge amount of work. If all you intend to do with it is to heat
something, there are easier methods. |
It appears you can phase lock microwave oven magnetrons!
http://arxiv.org/ftp/arxiv/papers/1407/1407.0304.pdf
https://accelconf.web.cern.ch/accelconf/IPAC10/papers/thpeb0...
https://accelconf.web.cern.ch/accelconf/IPAC10/papers/thpeb0...
http://dspace.mit.edu/bitstream/handle/1721.1/5013/RLE-TR-03...
http://eprints.lancs.ac.uk/26809/1/getPDF11.pdf
http://www.n5dux.com/ham/files/pdf/ATV%20Transmitter%20from%... Schematics for turning a nuker into an AM transmitter
I think it might be possible to run n x magnetrons into the same chamber. Just so long as you understand the control schemes.
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wg48
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Actually its relatively simple to add an other magnetron to a MO if both are powered by their own doubler circuit and transformer. Which is the usual
type of power supply in a domestic MO.
That doubler circuit only powers the magnetron on part of every other cycle of the mains power. By arranging the magnitrons to be powered on opposite
cycles of the mains power one is powered the other is not. Hence no interactions between their output powers. To achieve the opposite phasing of the
power supplies only requires the correct polarity to the primaries of the
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wg48
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Here is two magnetrons powered side by side IN THE OPEN
See https://m.youtube.com/watch?ebc=ANyPxKrIxUjlBLgEfwAftqRBla74...
It interesting to see the flashes on the ends of output stubs.
While two eggs are being cooked he stirred them holding a fork in his bear hand !#£%&.
DO NOT REPEAT THIS it exposures your body to potentially damaging power levels of microwaves.
[Edited on 16-5-2016 by wg48]
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Varmint
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Since the frequency is based on dimensions of the magnetron cavities and waveguides, you will "never" have 2 magnetrons operating at the same
frequency.
So, any hope of achieving phasing is essentially impossible.
Since the "aim" from each port is at a different angle, there will be little constructive nor destructive interference.
Yes, there will be some, but I suspect minimal as constructive and destructive interference rely, in large part on coherence of the waves in question.
Not coherent, different emission angles, different frequencies (of even only a few hz) means you can write off any dreams of constructive phasing, but
the upside is, you can similarly write off destructive.
I do have some concerns about the magnetrons interfering with one another, off-frequency energy entering the other magnetrons cavity might induce some
odd effects in the standing waves these devices rely on.
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Varmint
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Sharp and GE (possibly others) offer dual magnetron microwaves for commercial use. It would be interesting to examine one, because you can be certain
they've engineered their models properly.
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Oscilllator
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Sounds like a fun project. I have no idea about america, but in Australia many homes have three-phase 100A 240V at the switchboard, and the various
phases get routed to different circuits. That's a total of 24KW available power, so I don't see issues there  .
Why don't you just hook it up and see what happens? Provided all the magnetrons are inside a metal case and you are a safe distance away the worst
that could happen is the circuit breaker blowing, right?
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j_sum1
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US electrical supply is very different from Aus.
If I have my facts straight, residential supply is two phases of 110V (RMS) 180° apart and a neutral. So, 110V is standard. 220V is possible by
using both the phases. 3 phase is not so widely available.
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wg48
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| Quote: Originally posted by Varmint | | Sharp and GE (possibly others) offer dual magnetron microwaves for commercial use. It would be interesting to examine one, because you can be certain
they've engineered their models properly. |
I have received a dual magnetron commercial microwave oven Samsung CM1629. Each magnetron has it own half wave doubler power supply. I do not know if
the transformers are arranged such that magnetrons are powered on opposite cycles of the mains power.
Each magnetron has its own wave guide and opening to the oven chamber offset by about 30deg to each other. Curiously only in defrost are the
magnetrons powered alternatively. On all other power levels both magnetrons are on together with the usual on off variable ratio to adjust the total
power.
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