Easiest MOT Salvage Tutorial Pt.1

Video 1 of a series showing how I disassemble Microwave Oven Transformers (MOTs). This video takes you from a full microwave to a stripped down and separated transformer core ready for future projects. The only tools absolutely required are: a screwdriver, pliers, and a hammer. Only one part of the procedure is dangerous and I mention the safer alternatives.
Part 2: • Easiest MOT Salvage Tu...
Part 3: • Easiest MOT Salvage Tu...
Perhaps these videos will help you save money on tools or projects, or even make you a little bit of extra money off of the things you make with them. If you live in an underdeveloped country and are looking to start a business but can't afford (or even have anywhere to buy) the tools to startup but have access to junk, this is for you. If you're looking to buy nice tools later, having some trades experience with a cheap one can help you know what features you'll want.
Upcoming Projects: Spot welder, stick (arc) welder, plasma cutter, variac, hydroxy torch, carbon arc torch, arc furnace, battery welder, car (or other) battery charger and more.

[@ShimonKupferman]

Dear men, 1) I would very much like to thank you for the 3 videos on this topic that you have prepared - I think they can be said to contain the most extensive and high quality information I have found so far. Well done and thank you very much! 2) I wanted to offer, for those interested, you should also save the outer lid of the microwave, especially the upper part, because it can be easily cut (with vertical saw, for example) and use it for projects that need a small box (eg: car battery charger). Good luck to everyone, and do not forget to connect grounding ...!

[@ShimonKupferman]

I would like to highlight for the viewers: That the transformer's wire is usually a copper plated with very thin insulating material. If the insulation is damaged somewhere, it should cause an immediate short circuit (and electrocution if you touch it there...). So it is very very important not to scratch or rub anywhere the coil you thinking to use it.

[@petersack5074]

beautifull music at that interlude 6 7 minute mark......

[@MattsAwesomeStuff]

I described methods that are easy and work every time. MOTs have a variety of structures and materials. I've definitely mangled some coils using a vice, hammer, and so on. Some have sheared coils rather than break varnish free. To your question... "slag"? I'm not sure to what you refer. Enamel is the stuff the wires are coated with. Varnish is the stuff the coils (and sometimes xformer) are dipped in. "Slag" I'm not sure of. Elaborate your question & why, maybe I can help.

[@MattsAwesomeStuff]

Yes. While similar (or larger) in size to MOTs, UPS transformers are *not* easy to disassemble or rewind because they are built much better. Every E-I lamination is assembled in alternating direction, like a half-shuffled deck of cards, so there is no "EI" seam to cut (normal for almost any non-MOT). The only way to disassemble is to take a razor blade between each plate and then insert them again later. Using them as-is only helps if you want exactly 12V (actually 9-10Vac). If not, no point.

[@MattsAwesomeStuff]

@dansw0rkshop : 2 things buzz, core (if not tack welded or clamped well) and coils. If tight wound and tight packed, they're silent. I use an old old copy of Adobe Premiere, and most of the graphics are MS Painted (poorly) by me. Also, huge fan of yours, you're a unknowing mentor of mine. Hate your new website though. Everyone check out DansWorkshop for awesome MOT projects and other stuff.

[@MattsAwesomeStuff]

Not sure. Was it a 240V microwave? Perhaps your secondary is shorted (and thus actually drawing power?). No big deal, heat it up in an oven or on an electric stove instead. Or, try removing them cold. What you're describing means that the microwave would have tripped the breaker every time you tried to use it, even without a load.

[@MattsAwesomeStuff]

@blindabraxas : Ahh. No. Too much localized heat. And not enough. You're heating up 10 pounds of iron to 300'. However, you may have luck putting it right on the coil and softening the varnish right there. Maybe, probably not, because the iron will soak up the heat. *shrugs*. Only one way to find out, try it and see :)

[@MattsAwesomeStuff]

And yet, so many insist it's the better way. *shrugs*. Also, in future vids I'll show you how to use that secondary to make any new secondary so you don't have to buy new wire. So, can't do that if you chop it into 8" pieces.

[@MattsAwesomeStuff]

Well, you didn't describe what it is put together with instead of welds, so, I don't have anything to go on. I suggest using a hatchet or a triceratops.

[@MattsAwesomeStuff]

@blindabraxas Umm, what part? No? I have one, I never used it except for heatshrinking, and it's not necessary there either.

[@MrInnovativeEnergy]

Much better than chiseling the secondary off and having some cheesy looking rewind on the secondary..

[@malmailbggb]

i managed to separate the top part of the transformer, tried to heat it up using 240 volt on the primary coil, as you demonstrated, but the mains fuse blows every time, 13 amp 240 volt. i tested the leads, and the insulation, there is no short inside the transformer, but i can't do it that way..... why can't i power it up ?

[@TheDavelectronic]

Ok Matt not bad speedy, yet you need to be in that amount of time, oh i think you nicked or cut your finger along the way. Shallow welds, like you said, looks easy enough, good tutorial, look forward to the jig and the secondary rewind. Dave. Davelectronic.

[@HeartOfGermany]

Thank you, now I can use 3 MOTs to build a 230V to about 3x75V Transformers for my High Power Audio Amplifier. Hope, that an autotransformer will work on Amplifiers. :D Otherwhise I would need 6 MOTs to make it work, that would realy suck hard...

[@dearlydeceived]

I used to play with these in high school, didn't have any idea that it was this easy to separate..... I might have to go dig them out of my basement, they've been setting in mineral oil for almost 5 years but I think it might be a mess worth getting into.

[@blindabraxas]

Right around 6:20 where you heat up the transformer to get the coils out, either in an oven, toaster oven, or using the transformer heat loss itself? Why not use a heat gun to loosen it?

[@bramletyabercrombie]

Folks do die when they forget to unplug the microwave before talking it apart, so make very sure it's unplugged every time.

[@frame9539]

Hi, I need some help. I have very little electronics knowledge. However, I'm trying to build a power supply for my cordless power mitre saw. I've been told the best way forward is to use/adapt a microwave oven transformer. That's why I'm contacting you because your an expert and if you can help me, I will be grateful. My cordless mitre saw runs off 24v batteries ranging from 2.4ah to 3.0ah. The motor requires 630w of power. It's been suggested that I use a 700w use MOT and adapt it, rewire the secondary and so. Ok, that is were my knowledge ends. Can you please advise me the following; 1. What size MOT to use 700w or other 2. What size wire should I use on the secondary 4mm, 6mm and so on 3. How many turns does the secondary need 4. Do I need to use a bridge capacitor 5. Do I need any other electrical wiring or components 6. Does it need to be enclosed Please help as I really want to get this project off the ground. Kind regards

[@MattsAwesomeStuff]

Frame I am not an expert. I'm an amateur. I'll do my best. First, "Amp-hours" does not tell you how much power it draws, it tells you the quantity of energy in the batteries before they're empty. A plug-in saw has infinite amp-hours. Watts = Volts * Amps. So, if it's 630W and 24V, 630//24 = 26 amps. However, tools usually lie, and exaggerate their power, so, I'd guess it's 26A at most. An MOT would be perfect for this application. 1 - You can have too-big of an MOT, but a too-small one will just be like a battery that's a little bit drained, still work okay, just slower and easier to bog down. Also, the transformer will overheat (no matter what), so you can only give it a 10% duty cycle or so. Which, for a saw, is usually fine, you use it for 20 seconds then set up the next cut for a minute or two. 2 - These tutorial videos explain this. Use the formula I gave you, or, try your best then post and I'll double-check your math for you. 3 - Watch the tutorials. I explain clearly. Ballpark, about 1 turn per volt so, about 24 turns. WAIT. Except that's after you convert to DC, which ups your voltage by 1.4. So... 17 turns. You could give it a few more or a few less without much issue. 15-24 would probably be fine. More will give you more power, often 18v, 20v, 24v tools are all the same, just with bigger battery packs which cost more. Over-volting it by a few volts will make it more powerful, spin faster, and overheat a bit quicker. Undervolting it will bog it down easier and probably also overheat it because it'll be struggling to cut. 4 - I think your terms are mixed. "Bridge Rectifier" turns AC into pulsed DC. After this, usually a capacitor is added to smooth the the bumpy DC into flatter DC. Yes, you need both. The type of motor you have does not like lumpy DC and it will blow up if you feed it AC. Look up "50A bridge rectifier" on ebay, voltage rating doesn't matter, they're usually $2 for a 1" brick thing. Put it on an old CPU heatsink. 5 - I'd throw a 30 or 40A slow blow automotive fuse inserted to one of the output lines in there. Maybe another on the primary (120v or higher, ~10A). MOT to ~17v. Bridge Rectifier on the ~AC~ pins (polarity doesn't matter). Take the + and the - pins and hook them up to a ~50V (or higher, but higher is wasted) capacitor, as big as you can, might need to be like, cumulatively the size of your fist, more is better, it just smooths the power flatter and steadier (capacitor is a super-short-term battery). Use a grounded cable and attach the grounding wire to both the case and one side (any side) of the output wires. That'll blow the breaker if a wire comes loose and makes the case live. Use the microwave fan to keep the whole thing cool. 6 - Need, as in desert island, no. Personal responsibility. You'll have exposed 120V wiring which can be deadly. I personally would bend some of the sheet metal case into an enclosure, use the fins for fan flow. Best of luck. This is one of my future video plans. :)

[@alainarchambault2331]

I have no idea what the heck is going on. (total noob) I thought you wanted that thing and here you are taking it apart.

[@mrsayao]

Can you do a video about how do make a stick welder??

[@MattsAwesomeStuff]

Maybe. The heat will be too localized and intense I think. You'll ignite the insulation while the core works as a heatsink to keep the varnish from softening. What does work is a junk cookie sheet and an electric stove. Lay it on the burner, turn it to low-med, let the core heat up. Use oven mitts to move it. Heat is not necessary. As I showed, I did the first 10 or so cold, without it being suggested to use heat.

[@MattsAwesomeStuff]

Yes. It's easy, it's planned, it's mostly scripted, I just have to find time to shoot it. The spot welder video is first, (mostly shot), and the stick welder should be really easy to do after that because there's no mechanical setup, which is what's slow for me to film. If you want a very brief instruction, make a 30 turn secondary. Use the thinnest sticks you can find. Use two MOTs if you can. That's all a buzzbox is.

[@mikefromspace]

I'll have to make a video on this I see, I slightly opened the C shape before tapping out coils. Slag is a welding term for the 'junk' you don't want on the deal, in this case slang for that yellow glue (varnish?) . I've been soaking a coil in a large Adams peanut butter jar with acetone for an hour and shaking it, it's all coming off now. Hope I don't need to recoat epoxy but that stuff is baked on pretty good. btw I'm building a super over efficient device with this which I show in videos.

[@dansw0rkshop]

@MattsAwesomeStuff: Have you ever done the chiseling method just removing the secondary, for real? I've done it both ways, and my opinion is that leaving the core together and chiseling out the secondary is less work and the better way all around. The magnetic shunts are in fact necessary if you're going to run the MOT's original primary. Otherwise the inductance is wrong for 120VAC. Also, why remove all the insulating cardstock? If left in, then you don't need to put more back in later.

[@MattsAwesomeStuff]

@bramletyabercrombie : Absolutely, in fact, the part about plugging it in to warm it up is in there more because it was novel to me at the time (8 months ago) and creative, and I was talking to guys familiar with high voltage. If the half-page warning wasn't enough... DO NOT plug it in with an HV coil if you are not experienced with high voltage. "Instantly Lethal" is not an exaggeration. You'll drop dead before noticing you made a mistake. Just use an oven instead.

[@MattsAwesomeStuff]

Did you watch the videos? No point in a detailed tutorial if people don't watch it. Your question is well covered. And no, absolutely do not attempt to use an MOT in its original form.

[@MattsAwesomeStuff]

Either way. Almost always, an E-E core is superior to two MOTs. You have slightly less core, so slightly lower "core losses", maybe 5% efficiency difference. But either way you need two MOTs to make it. WATCH YOUR PHASES. Make sure primaries are coiled in the same direction (else wire one backwards) and have the same turns count (10-turn test both, add turns until they match). In this case, primaries are in parallel. Bottoms to bottoms, tops to tops (unless one is coiled opposite, then switch).

[@mikefromspace]

wOW YOU made this look hard! I used a diamond saw for the weld ($9). After that I just used a VICE and a chunk of steel I pounded on with a hammer, as the coils rested on the loose vice jaws, the iron falls out the bottom to the vice shaft. No damage to coils at all. I was watching this in hopes you'd answer this ; "How to get rid of slag on wire?" without harming varnish.

[@MattsAwesomeStuff]

Primary has thick (16g) wire. Secondary has thinner (28g) wire. Covered in tutorial. Inverter? - It usually says right on it somewhere on the front, since it's a selling feature. Also, narrower control panel (no big MOT in there). Also, not heavy lopsided weight (no 12 lbs of iron/copper on the control panel edge). Or when you take it apart, you'll see nothing like an MOT.

[@blindabraxas]

So would a heat gun make this a lot easier?

[@ITS.DA.IE-R]

I would die bro FR DIE if i tried that 😂

[@dansw0rkshop]

@MattsAwesomeStuff: I always had trouble with buzzing, they are never as quiet as originally when you open the core. I've tried all kinds of things, jb weld etc. Great job on the tutorial at any rate! What software you use for the montage, headings etc?

[@corbonzo1]

both the mots i got are connected by welds of the base plate. as well as the small welds. the base plate is spot welded to the E and I. what do i do?

[@MattsAwesomeStuff]

@dearlydeceived : One thing I don't emphasize enough in this vid... all my weld cuts are massively excessive. You're cutting maybe 1/16" (1mm), and double that at the corners. Grinding as deep as I showed leads to huge leakage and limits power. Also, I'm seriously pumped that I got you to dig up something from 5 years ago. Go build something! :)

[@MattsAwesomeStuff]

@dansw0rkshop : Chisel method, yes, several times. I can have the core apart before I could chisel the secondary out, but the real gains are in the re-winding stage. Disassembled is 50x faster. Shunts are not necessary, inductance isn't critical, depends on the project, and a better solution (if any) is extra windings which I show in part 3. Remove cardstock because it gets damaged often and because varnish is in the way. All explained in Part 3.

[@malmailbggb]

thank you for your advice, i heated it up in the oven, and managed to get the coil out, no damage, looked at it under a magnifiying glass. i think, these trafos, connect together inside the microwave primary in seriese with other devices inside thus removing possibility of a coil saturation of flux, also they use a 47 wat resistor on start up wich is switched over by relay and charging capacitor on the printed circuit board

[@ronknight1010]

Can you use a heat gun to warm it up

[@hughesis]

i Do have a question when attaching the AC power to the primary does it matter which way i attach the neutral and hot line to the primary?

[@MattsAwesomeStuff]

hughesis If you have just one transformer, then no. It matters for your grounding wire, but only in that you keep it consistent to your project.

[@renelange5789]

hi matt... nice video... got at question fore you - i have try to make this spot welder, but it takes to long time to weld, it gets to hot before i weld and the battery gets very hot - i got 230v in and 1.2 v out any ideas ?

[@jtsalsman]

What are the average specs (input V and output V) for these microwave transformers? could you just reuse them right out of the microwave?

[@RollerBGM]

gah, had one MOT that required loads of hammering to get the secondary out, as a result the laminations came apart... Epoxied it all back together but I'm betting the leakage of the core will be large now.

[@nourdine2326]

Hello, very nice videos thanks i've a question about MOTs well our electricity network is running on 230 volts and i've an old microwave that gives me a big heavy MOT that have a primary 230v in and secondary 21000v out its about 1600w the question is : in many videos on utub most of them use 120v MOT s so for buiding an arc welder they assemble 2 MOT in series "more MOT s more power" as its said so do i get to 2 MOTs of 230v to get a right arc welder? or just one do the job ? thanks

[@YummyMercury]

Epic tutorial bro, sub'd. Ive actually had an old MOT with the secondary removed lying around for a while, and i now need an isolation transformer, so this was helpful.

[@mrsayao]

Thanks for the tip! I can't wait to see your other videos! In your later video you talk about putting two large E's together, would that suffice or do you really need two separate MOTs?

[@ZeedijkMike]

I like your style. A little speedy but clear content. Just salvaged my 1st MOT but still haven't figured out if I should go high voltage i. e. as is and only for fun or low voltage - high current and build something useful.

[@okhascorpio]

well, this seems a lot more difficult than just cutting out secondary and punching it out. and a lot more likely to damage primary.

[@DIMTips]

Nice

[@MattsAwesomeStuff]

Cut through the base plate with your angle grinder or hacksaw.

[@hydrogen18]

Thank you for this video. I need to remove the shunts from the core for what I have planned.

[@mitropoulosilias]

:-) you da best!! subed and belled! Greetings from Greece!

[@kriss508]

nice shoes

[@mylittlespectacle]

Can't wait to see your other videos. Great job! Though I'm still scared to try

[@riff42]

Why take off the shunts?

[@MattsAwesomeStuff]

The shunts are there to limit the current. In most hobby applications, we're trying to squeeze every bit of power we can out over a short term, so we pay the penalty of worse efficiency to gain maximum power.

[@Hobbywelder617]

How do you tell the difference between the secondary and primary?

[@das250250]

Getting rid of the secondary.. Could build a wood |_| which hammers both ends out evenly ... Makes it quicker

[@Willeexd1337]

The Kaveman good Idea

[@sabbirahamed3183]

What is the gage(size of coil ware) of praimary coil copper ware of 800w microwave transformer

[@MattsAwesomeStuff]

It depends. Did you watch the videos? Usually 14-16g. Probably 16 AWG. 1.3mm.

[@TommyHelgevold]

Nice! That´s how a tutorial SHOULD be :)

[@yottky]

@5:13 if we use an angle grinder to cut open the transformer, would that damage the insulation between the laminations and increase the eddy current?

[@MattsAwesomeStuff]

If you damage the insulation, then yes, it damaged the insulation :p. Yes, it will increase eddy currents. There's no perfect way to do it, any cut is going to create some blurry touching places. But remember what was there before? A weld. A weld made all the laminations touch anyway. So, yes, it will make some eddys, but, if you do a decent job of it, the losses should be small enough to ignore (single digit percentage).

[@chitibusu]

Thanks, worked like a charm.

[@Hobbywelder617]

How do I know if it's an inverter microwave?

[@divyajnana]

THEE Best MOT vid series on KZbin by FAR; and they're only 480p....excellent, awesome, thank you. Can you suggest other appliances that have transformers or are MOTs the best as they are easy to disassemble? I.E., Just find smaller microwaves with smaller MOTs.

[@MattsAwesomeStuff]

+divyajnana Thanks for the kind words. MOTs are the best. If there was another appliance that was better, like, a fridge or something, we'd be calling them FOTs. Instead, the microwave takes all the glory. No other appliances have large, poorly constructed transformers that are coincidentally easy to re-wire. All other appliances are designed to work with household voltage either with motors (fridges, washing machines), or directly with heat (toasters, blowdriers, stoves) or both (dishwashers, dryers). Most electronic things are low power. Microwaves are unique in that they're electronic but require large amounts of power with a non-standard voltage. In order to use the magnetron to generate the microwaves that cook food, you need about 4000 volts. Can't do that without a transformer. I can't even name a close second. You might find a transformer in an old music amplifier that was a couple hundred watts (more likely 50-ish), and it will almost certainly be hard to rewire. If you can find old sodium or metal halide balasts ("high bays", you know those lights in school gyms that take several minutes to turn on), those are good for 1000+ watts but the cores are interwoven. Old style high bays that are magnetic are being phased out for more efficient electronic controls. The labor cost of commercial or industrial electricians is so high that they probably just throw them in the garbage so they'll be hard to intercept.

[@divyajnana]

+MattsAwesomeStuff Thanks for the quick response. Kinda smelled that one coming. Looking for a small and easy transformer rewind for a 230v transformer for a Chinese Hakko soldering station. Didn't want to try and rewire the secondaries to get 24 volts, too hard. MOT is got to be easier.

[@MattsAwesomeStuff]

+divyajnana One thing that just came to mind... a normal MOT is either 120v or 240v input to 2000v output. So, ~10:1 or 20:1. If you hook an MOT up backwards, plugging the coil with the thin wire into the outlet, the heavy gauge secondary should be either 12v or 24vac (depending on whether you're in a 120v or 240v country). That would be a damned easy way to step down the power you need. Then just rectify it with a bridge and smooth it with a cap. Gets you to the right ballpark anyway, just rip off turns from one or the other until it's right. It'll only be capable of maybe 60-100 watts because your input wires are so thing, but, the thing has so many turns per volt it would never even get warm.

[@divyajnana]

+MattsAwesomeStuff Thank you, good call. And i'm in Sandy Eggo, right next door to 240 volt Mexico.

[@RossPotts]

could you just use solvents to clean the varnish off? I'd rather just soak the damned thing overnight.

[@MattsAwesomeStuff]

I've tried all kinds of things and had others try others. Nothing worked. It's pretty resilient, purposefully so.

[@RossPotts]

MattsAwesomeStuff Good point I guess, considering the dangerous possible outcomes with a damaged transformer, especially on purpose...

[@lucakerschhackl5567]

What if you brake one of the copper wire in the primary coil??

[@MattsAwesomeStuff]

You have to repair it or throw it away. Carefully pull up the broken wire, put some enamel or Kapton tape underneath it, then solder on a new wire the same thickness to fill the gap. Heatshrink it or wrap with more Kapton tape on the outside. It will be lumpy but it might still work.

[@khellilg]

Nice channel man :)

[@ElectronPower]

can you please tell me what is the current draw on primary coil at 06:55? thanks :)

[@MattsAwesomeStuff]

With shunts, the waste heat of transformers is often still hundreds of watts. 500-700 watts for one this size I think. I just recently learned this. Without shunts, it's even higher (so better, for causing waste heat). But.. don't do this. Just put it on a burner on an electric stove to heat it. Much safer.

[@ElectronPower]

MattsAwesomeStuff Wow, and how is that? Is this normal even when you didn't cut the core weld yet? I mean when the transformer was factory welded, was current the same as after you disassembled the core? Yesterday I've cut the weld on the core and took off the secondary winding and now if I just put the "E" part of core on the "I" part of core I get about 3.7A of current at 235V even if it's unloaded, is this normal? Sorry for my english :P Thank you very much! :D

[@MattsAwesomeStuff]

Yeah, that was a virgin, unmodified transformer. I thought it was way too high, so I tested a couple others. They were all about the same. 3.7A @ 240v seems normal, yes, that's 870 watts waste. I'm still looking into it to describe it better and more conclusively. Seems like that means they're only 50% efficient, which is very low. I'm still learning too :)

[@ElectronPower]

MattsAwesomeStuff Thanks for reply! Now I assembled core back with zip ties, so it's really tight together and now i get only 3.2A at full input voltage. But what's intrusting is that its only 2A at 215V and then jumps up to 3.2 at 235V - so 1.2A difference within 20V. Do you know if those transformers are so unefficient even when they are not modified? I mean when they are still in microwave oven? Really thanks for that fast replies, I subbed to you mate! :D

[@MattsAwesomeStuff]

Yes, same out of the box. The reason they're so inefficient is because it's cheaper. Metal (copper especially) costs money, as does the silicon iron in the core. But microwave companies don't pay for the wasted electricity when you use it (which, to be fair, is also quite small cost-wise). The solution to the wasted heat is a larger core, more windings, and so on. No engineering challenge, just money. If you recall the part about "volts per turn", that gives you a hint at why the waste heat jumps with small changes. There is a sharp change in waste heat right up to the voltage used because they're designed to push the limits on saturation as far as they can. You can add extra windings and cut down on this if you care.

[@chancedrake2928]

If you were to have scuffed your primary winding, would that cause issues if you were to still use that winding?

[@MattsAwesomeStuff]

+Chance Drake - It depends. If you scuffed it and it is shorting two windings together, for example, shorting the 50th turn to the 70th turn... then you've effectively removed those 20 shorted turns from the coil. That would mean at minimum your ratio would be off, but also your transformer would overheat because it's too few windings per volt. Also, it's probably not a great connection, so it may spark and sputter at the short. If the primary is shorted to the core, or may vibrate until it does, that could make the body of the core live and dangerous to handle... depends on how you grounded it. If it's just a cosmetic scuff on the outside, not touching anything, just paint over it and add some electrical tape or whatnot for insulation to make sure it never does and you'd probably be fine.