Battery-Powered Magnetron
In this video I'll explain how a Magnetron works, collect some current/voltage numbers on a typical household magnetron from a microwave oven, and show how to power one off a 12V battery.
Typical DIY magnetron videos only show how to remove the transmitter from the microwave oven and run it with its original circuitry off mains power. Here, I'm basically building a high frequency inverter circuit to run off DC so that the entire device is portable. To do this, I have a ZVS oscillator driving a transformer primary, and the secondary coil is connected to a voltage doubler / rectifier to provide about 3.6 kV DC. There's also a low voltage / high current winding on the transformer to provide power for the Magnetron cathode filament.
One of the biggest frustrations of this project was trying to deliver enough current to the Magnetron cathode filament with my ZVS flyback transformer. It took a lot of messing around until i discovered that the filament has some RF chokes in series with it, giving it about 2.8 uH of inductance. At 40 KHz, this inductance resulted in too much impedance for enough current to flow. Fortunately, the fix was as simple as adding about 7 uF of capacitance in series with the filament to cancel out the inductive reactance.
With a proper waveguide, the microwaves could theoretically be focused into a relatively narrow beam, due to their small wavelength. However, that's a project in and of itself, which I'm not going to tackle in this video.
Output power of the 12V circuit in this video is only around 50-60W, but it can easily be increased by using a larger capacitor value in series with the voltage doubler on the transformer output. Be sure to use metal shielding around yourself and valuable electronics if you do this.
Schematic Link:
drive.google.com/file/d/1MyQg...
Music Used:
Local Forecast - Elevator
Kevin MacLeod - Bossa Antigua
Kevin MacLeod - Lobby Time
Topher Mohr and Alex Elena - Fortaleza
Exposure to an unshielded magnetron can result in permanent blindness pretty quickly. In the sense that a little exposure can produce a lot of damage. But you won't necessarily realise until a day or two afterwards. A friend of a friend lost 40% of their vision doing this. They were fine straight afterwards and then their vision went cloudy the next day. They didn't recover.
I'd like to take just a moment to appreciate that this is the first time I actually feel like I understand how a magnetron works.
Ladies and gentleman, THIS is what I'm talking about. True maker video right here. Technical, but didactic. Easy to follow with basic electronics knowledge and still going WAY beyond the boring flashy stuff you see on other channels. Packed full of content, building a cool idea, troubleshooting the many challenges and still, all withing 15min. Bravo! Amazing content as always Pirate, cheers!!!
Just to mention it. One of the big risks with this kinda RF is it can heat your corneas, you don't have the ability to feel heat there so you won't know it's happening. Once they get above ~40C or so the protein that makes up the lens of your eye will cook and at best you will lose the ability to focus your eyes. Generally you will get cataracts as well fairly rapidly after.
Ah why your transformer burned out was that when you balanced the impedance you nullified the cathode chokes that are hidden under the rear cover of the magnetron, the mismatch reflected the energy back into the magnetron and the cathode created a ready made antenna. Also the pink insulators are aluminum oxidide doped with either chromium or manganese. The BeO version is bright white and AFAIK the only commercially made oven magnetron that have those are super high power industrial ones or those from early 70's microwave ovens made by Amana.❤
I have a Masters in physics. I have taken I don’t know how many electromagnetism courses. This is the first explanation of a magnetron that has made sense.
“Curse this autism of mine.” I FELT THAT SHIT
One of the simplest most straight forward explanation of the working of a magnetron I've come across.
Something I rarely see mentioned (and occasionally not noted on the component itself) - the white plastic oval connector on the magnetron is actually a 15kv DC capacitor. Yup. I dont know if it routinely includes an integrated discharge resistor (with mgf variations i suppose its best to assume it doesnt unless you can confirm otherwise), but standard microwave tinkering rules apply - use caution! Obviously this can throw math when adding/subtracting capacitance and should be factored into resonance/tank circuit calculations and dont overlook these when salvaging components. Many thanks for the vids - I definitely appreciate a similarly twisted sense of curiosity, particularly when its going first lol
Give the next transformer and voltage multiplier a generous coat of epoxy resin to avoid the (
Remember the important rule from the amateur radio test: "Never gaze into the waveguide."
Also, magnetron + waveguide = EMP gun. IIRC those exist and work perfectly well cooking all unshielded electronics at a fair distance. And small animals. I used to be obsessed with this tech couple decades ago :D
I'm surprised more people haven't corrected you yet, but when a vacuum tube's grid is at zero volts the current is not cut off. To cut off the electron flow you need a negative voltage. For an anecdote, I was working on a guitar amplifier with poor contact to the output tube's grid pin and in less than a minute the anode started to glow red due to the uncontrolled current.
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What a brilliant explanation of a magnetron. Best I've ever seen, thanks.
would not be surprised if this guy got more knowledge than a phd. Not many people can explain the magnetron so well while having the civil/mechanical engineering background on hvac
what a wonderful and concise explanation of vacuum tubes. thank you for doing them justice
It'd be interesting to see if you can turn a microwave magetron into radar. Seeing how the story of how microwaves were made is cause some guy was messing with radar when it melted the chocolate in his pocket.
The filaments have 2 RFCs in the can too. That's where most of that inductance comes from. Great video
Ive messed with high power microwaves and you definitely feel the heat effects, its actually not that different than being close to a bonfire except the heat is not just on the skin, it has a few cm of penetration. The hands and fingers is were this is more noticeable, you feel them warm but instead of feeling immediate cooling as if you removed your hand from an IR source, with microwaves (2.45GHz) feels hot for longer because your whole finger warms up instead of just the surface.