One man’s microwave oven is another man’s hobby electronics store

Mads microwave teardown

There are loads of Internet content depicting the usefulness of salvaged innards found in defunct microwave ovens. [Mads Nielsen] is an emerging new vblogger with promising filming skills and intriguing beginner electronics content. He doesn’t bring anything new from the microwave oven to the dinner table, yet this video should be considered a primer for anybody looking to salvage components for their hobby bench. To save some time you can link in at the 5 minute mark when the feast of parts is laid out on the table. The multitude of good usable parts in these microwave ovens rolling out on curbsides, in dumpsters, and cheap at yard sales all over the country is staggering and mostly free for the picking.

The harvest here was: micro switches, X and Y rated mains capacitors, 8 amp fuse, timer control with bell and switches, slow turn geared synchronous 4 watt motor 5 rpm, high voltage capacitor marked 2100 W VAC 0.95 uF, special diodes which aren’t so useful in hobby electronics, light bulb, common mode choke, 20 watt 68 Ohm ceramic wire-wound resistor, AC fan motor with fan and thermostat cutout switches NT101 (normally closed).

All this can be salvaged and more if you find newer discarded units. Our summary continues after the break where you can also watch the video where [Mads] flashes each treasure. His trinkets are rated at 220 V but if you live in a 110 V country such components will be rated for 110 V.

Let’s don’t forget the high voltage (2000 V secondary) microwave oven transformer (MOT) which in newer microwaves is quickly being replaced by switch mode power supplies. DANGER! Don’t toy with this unless you really know what you’re doing! [Mads] knows, plus he plans on rewinding the transformer for much more useful high current low voltage applications. [Mads] needs only watch [Matt's] excellent videos on salvaging microwave oven transformers.

Not of terrible interest is the heart of the microwave oven, the magnetron tube which emits microwaves to heat your food. Don’t take apart the magnetron or play with it for several good reasons! First, there is the obvious danger of 2.45 GHz microwave radiation. Second, some magnetrons are made with a pink ceramic insulator containing beryllium oxide (beryllia). Beryllia is a known carcinogen and dangerous chemical hazard if broken up, handled or ingested.

Comments

  1. Admin says:

    I already know all about microwaves thanks to Jack Donaghy.
    *next*

  2. In general generic microwaves do not have beryllium ceramics in them, if they do they will have warnings stickers about it. These low power magnetrons dont dissipate enough heat to warrant beryllium. Things that do use it quite routinely, air cooled argon laser tubes and some kinds of x-ray tubes. Also some power semiconductors and resistors use a BeO substrate, especially in RF equipment. Again, everything I have ever seen that has BeO in it has stickers everywhere.

    If you do run into it and something breaks wet everything down and seal into a plastic bag and dispose of it.

    The table motors are pretty useless out of microwaves, they start in random directions.

    • WhiteThatch says:

      DIY 3d scanner?

    • ankilosafo says:

      Table motors are good for building coffee beans roasters. I once made one with this motor, metal grid bent in cylinder shape (making kind of a cage)and attached together through a Epson printer’s shaft. Perfect rpm (usually 2 – 3 rpm) and good that it is random in direction, as you can retain the cage and change the turning direction.

    • Claire says:

      If you remove a magnet by breaking it off with a screw driver and hammer and are not sure if it had the pink ceramic nor if any dust got on it… but if it did is the magnet incurably contaminated with the dust?

  3. cyc4015 says:

    I work as a theater technician, and I have to say, the motors I have scrapped from microwaves (or ordered as spare parts online) have come in handy so many times. We grabbed a few for a show last year, and used them for effect wheels in front of some lights. Worked great!

  4. gjai says:

    There’s a difference between salvaging useful components and collecting junk.

  5. BiOzZ says:

    i use a MOT, the diodes and the cap for a homemade capacitor charger … with a variac of course http://1.bp.blogspot.com/-M7uIVd-jkN8/TdX_iSz4a0I/AAAAAAAAAD4/jDDHEUoCE3w/s1600/BIO_3951.jpg

    and put it in a lunchbox because …. fun

  6. Anonymous says:

    The last couple ‘broken’ microwaves people have brought me stopped working because the big diode inside shorted. If you try to nuke a cup of water, but you just hear a loud buzzing sound and the water doesn’t heat up, that might be the problem.

    • Chris C. says:

      Great writeup!

      While the capacitor has an external bleeder resistor (visible connected between the terminals in the still shot), it is possible the resistor has failed. Unlikely, but it’s still wise to manually discharge the capacitor yourself, just in case.

      I second [Anonymous]‘ tip about the diode being the cause of many failures, and they are cheap to replace. I used to collect discarded microwaves from the curbside, fix them with a $3 diode, and gift them to broke college student friends who didn’t have one. Which they greatly appreciated. I could have sold some too if I wanted. So consider whether the microwave is worth more repaired, before stripping it for parts.

      And if you’re foolhardy enough to operate a magnetron outside of the oven (I admit I have), educate yourself very well on the dangers, including those specific to eyes. Testicles too, should your gender have them. Exactly how I protected them is a mental image I don’t care to share. ;)

  7. Tony says:

    The magnetrons aren’t useless, they have two hefty donut-shaped magnets in them. One on each side of the fins.

    Also the displays, ’cause VFD’s are pretty.

    The transformers on the main board often have two windings, 12v or 24v for the electronics (yes, sometimes the relays are 24v), but also a low voltage one (~3v) to drive the grid (screen? whatever) for the VFD. The 3v needs to be AC; so if you grab the display, don’t forget the transformer.

    Old microwave often have a very fine wire mesh inside the door window (new ones have just a foil sticker or something), that makes a good sifting filter.

    • ankilosafo says:

      Yeah! this door grid is good for crafting parchment with decoration patterns. They sell special punching grids for that, and they’re somehow expensive. Replace them with this door grid and you`ll be done

  8. Whatnot says:

    Not sure how useful a dirty fan at the end of its life is.

    Also; can’t you use the housing too? nice metal box with door. There must be some use for that.

    • nope says:

      They make a good faraday cage, because well, that’s what they’re designed for. Throw in an antenna and an electrical device you’re interesting in, and you can be studying crap in gnuradio in no time. Lots of gear gives off fun emissions once you begin searching.

    • StevenD says:

      I haven’t used the housing with the door but I’ve used the sheet metal cover as the a base/heat sink for a Stirling engine after sanding off all the paint. Not the greatest heat sink material but I needed sturdy but workable sheet metal.

    • Jim says:

      I used the body of an old microwave as the base for my food dehydrator.

    • Anonymous says:

      I put the fan and motor from a dead microwave into one of those 9″ desk fans. (The original motor pretty much seized; I hate sleeve bearings…) It works just as well as the original fan and is actually quieter.

    • emchammer says:

      The box it self it very nice enclosure for UV light etching, curing etc.
      I made one just by ripping the capacitor and MOT and putting UV LEDs inside the box, the original timer and safety switches in the door mechanism control the LEDs.
      Just put some reflective coating inside and make sure you paint the door…

    • pcf11 says:

      I used “a dirty fan at the end of its life” out of a microwave to cool a motor. It is still going strong many years later too. Actually there is very little that can go wrong with the fans out of a microwave oven that a drop of oil can’t fix.

      • Whatnot says:

        I’m told that even ball-bearing computer fans after a year or two start to become increasingly noisy as the wear take its toll on the ballbearings.
        But I guess with microwaves they don’t work 24/7 plus it depends on how old and used the microwave is.
        Anyway I guess I was being too negative.

        Lots of interesting ideas for the enclosure in this reply-thread btw, seems I was right on that one :)

        • pcf11 says:

          I’m told that sleeves are superior to ball bearings. If you check noise levels sleeved PC fans are quieter than ball bearing ones if everything else is equal. Although sleeves may fail sooner than ball bearings do if left unmaintained. I’ve brought some howling PC fans back to usefulness by lubricating them myself. Light oil won’t work though, I use chainsaw bar lube. That oil sticks like glue. I think it is even better than gear oil.

    • Chris C. says:

      It just occurred to me that the perforated metal shield inside the door might be usable as the stators in electrostatic speakers or headphones.

  9. Shanee says:

    Hello. It would be nice if the article could mention the dangers of taking apart a microwave without being careful of the high voltage capacitors. On many microwaves these store enough to kill (in theory) hours after the microwave was unplugged.

    • pcf11 says:

      Most of those capacitors have built in discharge resistors. If that resistor wasn’t there one of those capacitors might store a charge for a lot longer than hours too. Months, years? Who knows?

  10. Dodo says:

    Using the magnetron is quite dangerous. If you are careful to avoid RF exposure nothing should happen, but it will jam WiFi and other 2.4GHz equipment in a wide area. Without a proper antenna you probably will not produce that strong of a field to cause an exposure hazard. Note that the point where you feel pain (for 2.4GHz) is above the damage threshold, if you feel heat, stop immediately. For higher frequencies the risk gets lower and lower until it gets comparable to IR light exposure since they don’t penetrate as deep.

    A microwave oven cage is not a very good faraday cage. Very old ovens have real copper spring strips connecting the door the the frame when it is closed, this shields very well. Modern ovens simply have an opening that is tuned to be an open or short circuit for 2.4GHz. They shield well at 2.4GHz (60dB and more), but not outside. If you put a cell phone in the cage it will stay connected to the network.

    BTW: A normal kitchen magnetron will already oscillate if given 10-20W of power, which is much safer to experiment with. The signal unfortunately is very dirty, it produces a wide spectrum of noise instead of a single carrier. The spectral purity is much better if driven at only a few tens of watts. You can injection lock a magnetron (help it by pre-tuning it by adjusting the supply voltage), but don’t expect miracles. If you want a clean source you are better off with a surplus klystron or a solid state generator.

  11. KleenexCommando says:

    2.4 GHz RF radiation is more likely going to burn you (thermal burns, not “radiation” burns) than anything. Your lap-eggs are going to be just fine unless you go targeting them with the open waveguide of the maggy causing overheating of the tissue. People start throwing around the word “radiation” wrecklessly and people are dumb enough to assume ionizing radiation or “radioactivity” – niether apply to micowaves.

    And as for a faraday cage – yeah it’s a metal box and will block some RF from getting in or out, but it was designed for 2.4GHz and that doesn’t mean it’s going to work well at other frequencies, probably the lower the frequency, the less good it’s going to do.

    • Dodo says:

      RF thermal burns are still somewhat different from a contact thermal burn. 2.4GHz penetrates approximately 17mm in muscle tissue. Since you have no temperature sensitive nerves below 1-2mm the skin surface you don’t feel most of the energy. Unless you hold your hand in-front of a powered waveguide you will not get a spot burn, instead the whole area will be slowly heated. This is known to cause nerve damage (this also happens if you would touch a surface of 45-50 degrees for a very long time, but you wouldn’t do that as it would be uncomfortable.).

    • Whatnot says:

      Microwave radiation does long term damage to the eyes actually.
      And it’s advised to keep 2 feet (60cm) away from them while they are in operation. That’s official guidelines in a few countries and not just me making it up.
      The reason to keep a distance is the imperfection of the shielding of the door, which can easily be demonstrated and is a known thing.

      In other words no it’s not x-ray radiation, but everybody that visits HaD is aware of that, but yes things that are not x-rays can still do harm.

    • kmcloren says:

      Faeaday screen passes anything 1/4 wavelength or more. Rapidly attenuates lower, not higher, frequencies

  12. Merlin says:

    My most recent microwave salvage earned me an ethanol sensor. It was a good day.

  13. Fireboy says:

    ” special diodes which aren’t so useful in hobby electronics”
    Not true. They worked great in my Co2 laser power supply.

  14. zuul says:

    must have been an old microwave to have a knob and a bell, now it’s digital and a piezo

    i took the front panel off of a broken microwave we had from 2003, vfd, microcomputer, piezo/amp, relays and i think some stepdown transformer

    you could essentially use it as a clock/relay timer board…run other appliances for specific amounts of time

  15. Would anyone have an idea of the torque capability of these gear reduction motors?

  16. Re. VFDs, I have a fair few here including a bargraph one and PCB with driver ICs from some old analyzer.
    If someone wants to take them off my hands for the cost of the postage, I am on 4HV and also mandoline at cwgsy dot net

    Please be aware that some very old microwaves use PCB based oil in the capacitors and this can be dangerous if it has leaked.
    Also worth mentioning is that the MOTs on some newer models use aluminum in place of the more expensive copper for the coils.
    They typically deliver 5.2KV at up to an amp which is enough to electrocute an elephant (!) even in the short time before the ELCB trips.
    The capacitors can also store a fair wallop and collateral damage can result even if the shock isn’t fatal such as hitting a sharp edge etc due to reflex actions.
    One hand behind back, etc at all times when working on these.

    -A

  17. aztraph says:

    Tidbits from a guy who repairs microwaves for a living:

    I am personally glad he takes them apart because that means some fool isn’t going to try to mess with it and get themselves killed.

    that first micro switch had been overheated, you could tell by the discoloration so don’t rely on it for anything important.

    The transformer is good for making spot welders or getting yourself killed, leave it alone. the magnetron is good for the 2 magnets (if they haven’t gotten cracked due to overheating.

    the capacitor rating (uf) is related to the cabinet size the microwave, I believe the smaller the microwave the larger the cavity, but I could have that backwards.

    last but not least: UNDER NO CIRCUMSTANCES SHOULD YOU EVER DISMANTLE A MICROWAVE FOR THE PURPOSE OF SALVAGING PARTS BEFORE YOU PHYSICALLY CUT/REMOVE THE CORD SO SOME ASSHOLE DOESN’T PLUG IT IN WHILE YOU ARE WORKING ON IT.

    • Chris C. says:

      I cut off the cord off appliances, but for a different reason – if the “carcass” is going to a curb or dumpster where someone might collect and attempt to use it, and I’ve left it in a state where it could be hazardous to plug in.

      • pcf11 says:

        Anyone that plugs something in they picked up off the curb without taking reasonable precautions advances our species. Think of it as a modern engine of evolution if that makes you more comfortable. That leads me to think of another use for discarded microwaves in fact. I used to pick trash at this one great transfer station that also attracted this other fellow that removed all power cords to scrap them. I could have modified a microwave oven so the large capacitor inside it was connected directly to the power cord, then charged it, and left it for him to trim. Thin the herd so to speak.

      • Whatnot says:

        There is a whole culture of people that salvage devices from the curb and repair them, so it’s a bit annoying that they have to go source plugs then.
        But it’s not the worse of it, in modern times they push more and more for you to bring your electronic devices to a specific dump, and now they reached a point that it has been made illegal to dump electronics with the garbage collecting service in a few places/countries.

        Freaking stupid because instead of people re-using stuff it’s destroyed in a energy-wasteful manner and often enough leaving toxic sludge. Or shipped to 3rd world countries where unprotected and uneducated people get told to disassemble it all while they slowly poison themselves.

  18. spag says:

    You can get a pretty good voltage by spinning the turntable motor by hand. Couple hundred.

  19. Cool, thanks for the tip spag

    I’ve also been experimenting with “broken” MWs, and concluded that most of the time if the magnetron heater and waveguide cap is intact and the magnets aren’t cracked then something else is broken.
    Usually these break due to low emission but this can be fixed with a simple modification like running just the heater from a variable voltage/current supply at slightly elevated voltage ie 10V AC instead of the usual 6.3VAC and this “unmucks” the poisoning by cracking the surface a little bit.
    It won’t last long but for projects where the magnetron is being overloaded this can be an advantage :-)

    Also worth a try if you have a cracked magnet is to remove the bits of smashed ferrite and position some rectangular NIB’s around the casing in a circle.
    I’ve not done this yet but this can sometimes work…
    #include “DANGERYOUMAYDIEHORRIBLYSODONTSUEME.h”

  20. Shox says:

    Is there an easy way to tell if there is beryllium in the ceramics? From what I found beryllium is some pretty nasty stuff and should be avoided. Are the magnetrons in larger microwaves coated with the stuff?

  21. Gadgetz says:

    The magnets aren’t coated with beryllium. It’s the ceramic insulators thar may be made from beryllium. The insulators are safe to touch and handle, as long as they are not scratched or broken. The ferrite magnets are pretty strong, and well worth the effort imho.

  22. Irish says:

    I’ve had to replace the control panel in two microwave ovens, there are a few good hobby electronics parts there too. I’ve found a few 1% resistors, some PCB relays, the IC which controls the whole thing (not sure of it’s aftermarket use though), and of course the VFD that we all know is becoming popular to re-utilize.

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