How To: Rewind Microwave Oven Transformer, Trash To Treasure!

Turning trash into treasure! In this video I show you how I rewind a transformer salvaged from a microwave oven.
Parts/consumables used:
Microwave transformer
8m (or more for higher voltage) insulated copper wire
Silicone caulking
Masking tape
Scrap wood
Zip-ties
Information provided in this video is for educational purposes only.
If you attempt to recreate/replicate anything you’ve seen in this Or any other video, you’re doing so at your own risk.
- Schematix -
Thanks to NCS for the music!
End track: Different Heaven - Far Away • Different Heaven - Far...
Different Heaven FB page: / differentheaven

[@jameswiz]

OH MY GOD!!!!! WOW!!! HE SPEAKS!!! THANK YOU!! THANK YOU, THANK YOU, THANK YOU, for not just playing shit music, or typing words on the screen during editing!!! By far. The ONLY REAL Rewinding Transformers Video IVE SEEN!!!! WOW!!! GREAT JOB, JUST BECAUSE YOU SPEAK!!!! And I bet I know why you speak. Because you actually know what you're doing and why it works. Not just "HOW" to do it, like most of the hacks out there making videos with music and text that just tell you DO THIS!!! And don't explain a thing. YOU KNOW WHAT YOURE DOING@@@ YAY!!!! BEST VIDEO!!!

[@1959Berre]

Excellent video. Well explained, well demonstrated, well presented. And no irritating background music, for which you earn my eternal gratitude.

[@cody3300]

Fully agree, no music needed

[@yz8302]

I used to rewind small transformers when I was teenager back to 30 plus years ago. This video just let me recall all the steps I encountered like cutting punching measursing guessing patching... I very much enjoyed the work I did. Thank you very much and great work you have acomplished.

[@InssiAjaton]

It appears this is mostly a mechanical how-to. Maybe it helps if I add some electrical comments. First, there are some manufacturer data sheets for transformer sizing. Generally the more power required, the heavier the core becomes, KEEPING the line frequency the same. A higher frequency allows reduced weight, up to a limit. Above some 400 Hz, you need better (thinner laminations and those insulated from each other, also no more welds) materials and above 20 kHz you likely need to switch over to ferrites. Then, the optimum tradeoff between core and winding heat losses comes at near 1:1 ratio of the iron cross area and the window (core space) cross area. The winding formula is n = U/(4.44 f b A), where n is number of turns, U is the applied RMS voltage, f is the frequency, b is the allowed peak magnetic field and A is the iron cross section. All these in the metric system, i.e., the A is in square meters and b is in teslas. The b depends on the iron quality and varies from 1.2 to 1.3 for most practical materials and some 1.55 to 1.7 for some crystal oriented materials. Then, about the shunts - they are actually causing leakage magnetic field ("radiation"). Their purpose in the microwave oven is to LIMIT the current. As such, they also cause additional heating of the transformer. Along with too few turns in the primary, they are a cause of higher primary current (which was a concern in another comment). For a bench power supply, where you should do current limit in electronics, you should replace those shunts with some wood or plastic strips. That would improve your efficiency, although it would increase your INRUSH current, as the limiting action is discarded. I hope this info still reaches some people who might benefit from it.

[@MrBrymstond]

Would it be any better if we used a piece of plastic and one metal shunt then another piece of plastic, I'm new at this, thanks

[@illumiNOTme326]

Great info!

[@kolinevans9127]

Pellervo Kaskinen thanks for the info , for anything related to laminate I use the 42 constant, which is the Ae area effective divided by 42 I.e 42/ Ae = Tpv Tpv = turns per volt I have tested this extensively and can not fault it including ‘blind’ tests where I used it to predict the turns then unwind various ‘consumer’ windings to find it accurate, even on large turn numbers, however this equivalent may help with trying to derive a new ‘constant’ for various crystal hybrids so thank you . I don’t have my book here immediately but yes the primary of a microwave Transformer has missing meters worth of inductor based both on the 42 constant and on me predicting then unwinding. I believe it was missing many meters. This and other factors contribute to the excessive heat and energy loss that these lovable and famous devices radiate. Regards.

[@BengtRosini13]

Pellervo Kaskinen I think I understand about 50 % of that.

[@theq4602]

I have a question for you since you seem electrically inclined. I'm looking to rewind one of these transformers for an even higher voltage by grinding off the weld and pulling the "E" "I" sections apart to access the core. I'm wanting to build a secondary out of 32 AWG wire with about 32000 turns to get roughly 30000v at 30mA. Will this turn count be sufficient? Assume I take the necessary precautions such as yellow tape bettween layers, in addition it will be submerged in mineral oil. Supply power will be fed to a variac and the output of the variac to a bridge rectifier (no capacitors) with a 15amp fuse that feeds the primary winding which will be kept untouched. Will such a setup work?

[@love7192]

Great Work, patience in explaining and teaching style 👍🏽 With the wire melting, you could just go in for a heat resistance insulation cable or wire for that "MICA FIBER COATED CABLE".

[@jimviau327]

Great vid bro. Thanks. Just a add on, for those who need a 2xVAC with center tap, just double the wire turns and pull a tap at half the turns. Of course wire diameter will limit the possible number of turn. One can use enamelled wire instead of PVC insulated to lower the overall wire area necessary.

[@katoyimaenriqoup7366]

GOOD LECTURE, HE KNOWS HOW TO EXPLAIN TO PEOPLE WHO ARE STILL LEARNING, GREAT JOB BOSS

[@ScinnerNo1]

Just drive the shunts a bit not all the way. That way they protect the primary from the hacksaw.

[@josephgkrestan3044]

Great information as usual! Thank you for your excellent instruction! Thank you again. Joe

[@Philhoppermiller]

I just finished cutting the secondary winding out of a transformer. I am following your directions for the winding. I want to make a 24 volt- 10 amp unit to power a CNC machine. I have all the parts except a transformer & a 10 watt resistor. I can get the resistor locally. But the transformer was a bit pricy. So I found a broken micro wave and stripped it down for the parts. My transformer has a solid core between the primary and the secondary that I did not have to take out before I stripped out the secondary and the shunt wires. Thank you for the instructions.

[@Schematix]

Thanks :)

[@keithfehmi4243]

@Schematix pls leave an email address I can email you via?

[@taunteratwill1787]

ARCSTREAMS Amp meter?

[@MrLibbyloulou]

Well, i think that was very interesting, didn't know it was that easy to do.....keep making vids like these please

[@tr_2sc1970]

Just a few hour ago, I got rid of the secondary winding painfully. Then I removed the shunts because they helped protect the primary winding while drilling and hammering the secondary winding. By the way the windings are Aluminum, so be very careful not to damage the primary as its not easy to repair or solder. The outer surface of the primary winding got a bit of a scratch, it's dangerous it touching while connected to power. So I covered it with lacquer.

[@bookwizards]

Great Video I found a discarded microwave and am pulling the transformer. The pace of the video is slow enough to be able to take notes. I am building Your Bench supply as I am recently retired and have been using an old PC supply at home for 30 years but miss the bench supplies I had at work so am looking foreword to spending some time teaching my grandkids electronics.

[@andrewferg8737]

Very informative. Thanks for sharing!

[@ed-jf3xh]

With the size wire you are using for the secondary, I would watch for excessive heating, even at 10 amps. Remember, the normal current rating for hookup wire is in free space where it is cooled. When you put it in a tight coil, it can't cool as easily. Use larger wire with thinner, higher temperature insulation, less heat. Play it safe.

[@geartech3860]

That is definitely the wrong type of wire,enameled wire is best,not worth taking short cuts.Very dangerous stuff your playing with.Transformers heat up a bit so you have to think about the long term usage.Think safety always. Good luck!!

[@marklowe7431]

Excellent instructor/video. Great that you explain the safety. Very important.

[@scroungasworkshop4663]

Not a bad tutorial........for a Kiwi. Seriously though this is just what I was looking for as I have collected plenty of microwave transformers and I am looking to make an electromagnetic chuck/ machining plate. I had it pretty well sorted except for a power supply. I was looking for something around 40 - 50 volts dc but they are thin on the ground and as you said expensive but now you have shown me the way. I figure if I build a transformer like you have shown and configure it to put out about 35 volt Ac and then pass it through a bridge rectifier I should end up with around 42 v dc. Dc giving a stronger magnetic field. Thanks again mate. Cheers Stuart 🇦🇺

[@fuorman4872]

how you get 42dc from 35ac ?! and i advise you to take many line from secondary so you get many ac volt sorry about my stupid english and did you know what wire gage or size he use for 15 amp ?

[@scroungasworkshop4663]

Fuorman. Hi Fuorman, I believe that when the AC goes through the rectifier you get an increase in voltage.

[@fuorman4872]

@@scroungasworkshop4663 Thinks for the idea I will try it and tell you soon I think diodes reduce voltage but maybe there's something i miss Stay safe and take care my friend

[@scroungasworkshop4663]

Fuorman. I thought so to so maybe I am wrong. Please let me know how it goes. You stay safe as well my friend. Cheers Stuart, Australia 🇦🇺

[@j.f.christ8421]

@@scroungasworkshop4663 AC voltages are usually given as RMS while the peak is ~50% higher, eg 240v has a peak of 325v. Your bridge rectifier converts peak AC to DC, so it comes out higher. The bridge has 2 diodes and will drop about 0.6v each. RMS is the DC equivalent of peak AC, so a resistor at 325v AC (peak) will put out the same amount of heat as one connected to 240v DC..

[@ilducedimas]

I kept hearing "I just did tin tunes on the secondary windings". Great video !

[@MichaelBeeny]

The letter E does not exist here in NZ. Just substitute every E with an I and you too will soon become a Kiwi.

[@TheDrewsifa]

Yeah us Kiwis are not too keen on vowels, so we decided to only use one. This is how you can tell us apart from the Aussies. They like vowels so much, that when they get to one they just hold onto it for as long as possible. Geeedaaaay Maaaaate.🤠

[@heyderaliyev8976]

I wish I`d see your off camera AMP TEST of this hand-made transformer/ it looks great /Thank you man

[@user-be4yc2vr5c]

great tutorial! Saved me some troubles and just gonna re purpose my surplus of microwave transformers haha. Wish they made it so you could salvage and re purpose all of it. Having to cut it apart it kinda bad design tho I know why they claim to do it that way. =/ Oh also, my only critique for safety purposes would be when conducting the test to make sure the transformer isn't grounded, make sure to test that the place your grounding from is in fact a good ground contact point by touching lead to where you would like to have ground point and another random spot on the former with another. This leaves no room for error really. Or at least reduces it severly as I know I've had times where I thought I was on good grounds but was in fact weren't and double checking like that really saved me! Thanks again bud!~

[@moya9450]

This is not practical at all. This transformer gets Extremly hot under normal load. Because the input power is too much. I tried many time in the past to build high current power supply out of it, but no hope. Only you can built Spot welder.

[@derofromdown-under2832]

Great vid, well done!!! 10/10

[@CrackerJayherber]

As an apprentice EMST/Winder I really appreciate your videos

[@Schematix]

You're welcome :)

[@gerryroberts5971]

He sure has a face for radio, but his knowledge is really top rate.

[@jimmyfavereau]

Awesome! Thanks for sharing!!!

[@taunteratwill1787]

Jimmy Favereau Yeah "Thsnks" to you too!

[@Centar1964]

MOTs are made as cheaply as possible and are NOT meant for continuous service...the idle current is way too high due to the absolute minimum number of windings in the primary, you need to add 10 to 20 turns in series with the primary for continuous service which will reduce the idle current a lot. Also it is way easier to use an angle grinder to grind off the welds holding the "I" and "E" sections together and then push the primary off in one piece, you can then reuse this wire for something else...MOTs are great for making DIY transformers, light dimming chokes (even variable with adjustable "I" section gap, I have even made audio output and speaker impedance matching autotransformers with them...

[@jallowsaidou1639]

interesting, thanks for sharing

[@user-bd2id5yf9g]

Got a couple of microwave transformers with the 240v winding primaries on. Got a couple of empty ones too, after I damaged the primaries. Building a circuit board with an output of 12v ac from H-Bridge Mosfets to produce a pure sine wave at 50 Hz. Each Mosfet is max 110 amps at 55 volts Max. I'll be gating them for 12 volts sinewave. I've also got 13 meters of enameled 3 mm transformer wire I'd like to use in the transformer. You say 1.04 volts per turn. It that in rms values or peak values. I thought I'd have to use 21 turns to get 12volts. I want to also wire in a centre tapped 12v ac output to gate slave mosfets to get between 3kw to 7kw output, depending on the transformer. This design is for a low frequency output using a H-bridge, I'd use the slave after it. But, I also.. want to use spare transformer primary winding to get to 400 volts plus, maybe up to nearly 600 volts. That is for the high frequency inverter output version. I've got the 600 volt, 47 A Mosfets for that. Be good to use that as a final output. I'd use a separate push pull circuit to generate an AC output, where I can control the voltage & frequency output, even change the wave form output using a filter circuit.. have a choice of square, trapezoidal, sawtooth or sine wave. Could then use the pulsed DC motor controller to drive an electric generator using frequency control. So, how many turns do I need for 12 volt RMS output? 11? or 12? I'd like to know how many turns to add on the primary side using the same enabled wire to boost it to 380 to 450 say. Thanks for the video, I learned more about transformers.

[@Luxeontech]

Good mechanical and electrical performance. Best regards from the technical laboratory Ulm von Walter!

[@chrisbraid2907]

My experience is that if I rectify a transformer then my output voltage will drop a little. Might be good to fit a bridge rectifer before final testing to see if it’s the voltage you wanted.nice straightforward demo ....

[@thereynolds2725]

Adding a capacitor after the rectifier will boost the voltage to the AC peak.

[@leonreynolds77]

Video should be titled: "How to rewind a microwave transformer into a step down transformer power supply."

[@NavinBetamax]

@Michael Reynolds..... upcomming DIY video.........How to rewire a Video Title ....!!! Lol !

[@SHANUSHAH]

well done, greate video, very informative, Thank you

[@tommieweaver6325]

Great Job explaining and showing. I tried what you did but messed up primary.

[@carnright]

Awesome just found your channel now I can binge watch them :-D

[@Laziter73]

Nice tutorial :) I happen to have an old microwave oven in my basement, I'm going to give a new life using your video as a guide, thank you very much :)

[@Schematix]

No problem :)

[@aurorasinplex5947]

@@Schematix gov will have all heads for this tech thay teach us that we always have loss but never talk about the converted gain we can make from eletromagnets if u convert all the wast thermal energy around you u can use it universally as energy u need a true sine wave bipolar like the power comp dose a true pure sinewave like a grid tie inverter once the signal is made the system will turn on and consume wast thermal energy from the environment and space around you... there is free energy but it comes from Universal thermal loss and converted into a gain. so a pole Transformer and a microwave Transformer have a common between each other u can take 2 microwave Transformer provide a pure sine wave grid tie inverter to it or a true bipolar sinewave that inter acts with nature in a perfect spherical motion like a flower of life.. if ur home provides this use it as a Source signal then u can simply stack the Transformers on top of eachother in correct fasion and note that the 1 wire on the Transformer must stay connected and the other disconnected your only useing 1 wire on the hi side .. so test ur self 2 microwave transformer stacked on top of eachother same face sides. one side 120 to the wall and the other 120 side to what u want to power and useing the Transformer just the way it came out the microwave with the wire attached causes the energy in its perfect spherical motion to converted wast thermal energy to amp for u hot to cold in to out... should look a bit nuts with u use a form of wireless energy but its interacting with the environment...this is my work a compilation of Otis car. Tesla. and many other very smart people nowadays i think i found the gate source and drainif this gets out to much that it works the power comp and mib will have our headsdont do this at home warning high voltage yet i cant stop u lol DO NOT TOCH THE CORES OR THE WIRES OK u will die make sure u dont touch the core if the hi wire is mounted to it u dont have to mount the hi on the core if u dont want u connect the 1 hi wire to the same side hi on the other transformer then the core should besafe to handle if nessary

[@aurorasinplex5947]

@@Schematix gov will have all heads for this tech thay teach us that we always have loss but never talk about the converted gain we can make from eletromagnets if u convert all the wast thermal energy around you u can use it universally as energy u need a true sine wave bipolar like the power comp dose a true pure sinewave like a grid tie inverter once the signal is made the system will turn on and consume wast thermal energy from the environment and space around you... there is free energy but it comes from Universal thermal loss and converted into a gain. so a pole Transformer and a microwave Transformer have a common between each other u can take 2 microwave Transformer provide a pure sine wave grid tie inverter to it or a true bipolar sinewave that inter acts with nature in a perfect spherical motion like a flower of life.. if ur home provides this use it as a Source signal then u can simply stack the Transformers on top of eachother in correct fasion and note that the 1 wire on the Transformer must stay connected and the other disconnected your only useing 1 wire on the hi side .. so test ur self 2 microwave transformer stacked on top of eachother same face sides. one side 120 to the wall and the other 120 side to what u want to power and useing the Transformer just the way it came out the microwave with the wire attached causes the energy in its perfect spherical motion to converted wast thermal energy to amp for u hot to cold in to out... should look a bit nuts with u use a form of wireless energy but its interacting with the environment...this is my work a compilation of Otis car. Tesla. and many other very smart people nowadays i think i found the gate source and drainif this gets out to much that it works the power comp and mib will have our headsdont do this at home warning high voltage yet i cant stop u lol DO NOT TOCH THE CORES OR THE WIRES OK u will die make sure u dont touch the core if the hi wire is mounted to it u dont have to mount the hi on the core if u dont want u connect the 1 hi wire to the same side hi on the other transformer then the core should besafe to handle if nessary

[@brotherricksafety]

So what will you do with the 21 volts

[@michaelmurray3422]

You will be surprised at how much current draw on the primary with no load on the secondary. It will be around 10 amps. If you kept it running for over 20 minutes or more, you couldn't touch it. You need to add some windings to the primary, ( around 30 turns ), because the amount of windings that it came with is wound for max load ( It's under wound for a reason ). That will also knock down the loud buz from the 60hz and the current draw with no load on the primary will be a lot lower ( around 1 amp ). This will not change the secondary output, it just won't catch on fire. I would rather draw 1 amp with no load than 10 amps with no load, and keep my house from burning down.

[@ecobob101]

Can you use 2 12v Transformers. Connect the secondary, and create an isolation transformer?

[@NonnofYobiznes]

I just wanted a bright flashlight... I learned about flashlights, which led me to batteries, which led me to power packs, which led me to battery balancing, which led me to variable power supplies, which led me to "make your own PS", which led me to transformers... here I am learning about how to make your own transformer... where am I going from here? How to harness the power of the sun to power your power supply? I feel like I'm a in a free fall... I just wanted a bright flashlight...

[@TheBlackadder-Edmund]

I just wanted a new external battery for my phone...

[@taunteratwill1787]

You talk too much. . . . . .

[@rccola3368]

Taunter Atwill somebody has to tell them!

[@stefanryznyk9804]

We seem to have had very similar paths! I'm now working with solar, supercapacitors, and solid state batteries. It's an addiction.

[@Isolierter_Hazim]

And that's how I'm into electronics.

[@ZeedijkMike]

Great video. Just a note though. The wire can manage 15 Amps, but not when it wound in a coil. The 15 Amps are for normal installation.

[@taunteratwill1787]

Zeedijk Mike Peak values.

[@vtrandal]

I will try this but I'm going straight to cutting the secondary coil with the hacksaw. I'm skipping the step of removing the shunts before removing the secondary. I'm hoping the shunts are easier to remove after removing the secondary. [Oh!] Now I see the secondary is glued in place as you said and the shunts prevent levering it out. Okay. Nice work. Thank you.

[@petersack5074]

hi thanks for this....advice= use an angle grinder, (i use homemade steel chopsaw 14 inch)to cutoff secondary.Shunts are needed in the redone core, as well, to separate magnetism. Also, a ground down railroad spike works best, to hammer out secondary core...fits like a glove. I've done many of them.......alternatively, also grinding off the welds, and take-apart the core.....works as well....then, weld up when done winding secondary bobbin.....

[@taunteratwill1787]

If you paid 10 dollar for that small amount of wire, you got ripped mate!

[@hannelmahinay6288]

bro what is the size of thhn wire you used for the secondary rewinding?? and i want also to know how much the a.c input of the primary in order for you to rewind the secondary winding..? thank!

[@bogywankenobi3959]

Throw those shunts away! They reduce the efficiency of the transformer by storing magnetic flux instead of letting it pass through the secondary winding to the core material on the "other side" of the secondary. By distorting the sine wave passing through the secondary, they also add a hideous amount of harmonic distortion to the output. Those shunts are how they turn a 1500 Watt device into a 1000 watt device.

[@phbrinsden]

I did a rewind of one of these and tossed the shunt strips. I was wondering whether I made a mistake when I saw this. Can someone explain exactly what they are there for?

[@bogywankenobi3959]

@@phbrinsden: Here's the thing - iron and steel can hold a lot more magnetic field than air.can. So in an un-shunted transformer, when the magnetic field starts increasing around the primary wires it can swiftly move through the air, cut through the secondary windings, and then get stored in the steel core where it moves much more slowly due to the steel being able to hold a much denser magnetic field. You are giving the magnetic field someplace to go after it has crossed the secondary windings. But if the magnetic field has to go through a shunt before it passes through the secondaries, the shunt is going to store the field until it saturates, and only then will it start releasing the stored field into the air on the secondary side of the shunt to then pass through the secondary windings and then it will be stored in the core steel. But some of the magnetic field generated by the primaries is always going to be stored in that shunt and never reach the secondary windings. They can very effectively tune the power output of the transformer this way. It also lowers the voltage on the secondary side of the transformer, as well as introducing several harmonics of the original 60 hertz input wave.

[@phbrinsden]

Bogy Wan Kenobi Awesome, thanks for explanation.

[@lupojacobo9892]

Thanks for sharing

[@hannuanttila6362]

Great video, thanks! 👍🙂

[@andreluizpiva39]

Nice video, greetings from Brazil!

[@victorreppeto7050]

There is a formula 4 the number of windings the primary and secondary. If you only change the number of turns on the secondary then the Transformer is no longer at Max efficiency. Am I correct? Another important detail I wish you'd covered was Magnet Wire versus insulated wire. I still learned a lot from the video. I really enjoyed it. Thank you.

[@JamesP6084]

Well done great video :-)

[@NeonblueIndustries]

which is why you should leave the shunts in after you have pushed them out enough so they cover the primary as a shield....

[@phonybobsmail1680]

Hey man!! Awesome video. I'll be doing this to power an electrolysis chamber to launch marbles in my "marble machine".....very informative, thanks!! I see lots of interesting videos on your site, and I just subscribed!!

[@w9x7cv3vg6]

ohhhh i pickem up off the roads,i have 10 to take apart,getting the high voltage caps and diodes which can be used to make lightning generators and even power hamradio amps

[@dragan3290]

Top job.😊

[@royspeakman1157]

VERY GOOD ! DONT STOP !

[@LEO-xo9cz]

Really nice video!

[@stephenschaffer4304]

you are an excellent teacher!!

[@electronicdiy3738]

what's the resistance value of 20 turns of secondary coil so we can make a centertaped transformer to build an inverter DC > AC thank you

[@qaisarawan93]

nice video I tried to make a spot welder. For it i bought a used MOT, the seller connected ac voltage to the primary winding (thin wire side). And it created humming sound. At home I removed that side and when I connected ac to the secondary side it created smoke and smell and became very hot to touch. Seems like the Secondary was already short? What you say? Also Now can i rewind it using suitable size enameled wire? Will winding it with slightly thinner wire be ok for spot welding? Current winding is using 0.9mm enameled copper wire and the length and breadth of cross sectional area is 15 by 17 mm..

[@RegisBeaken-bk3xg]

I didn't see what size wire you used when you did the 21 windings. Loved the video and hope to see more

[@victorkoren1989]

What about the magnetizing current? I checked the primary current of 4.5A from the 220V mains without having a secondary wound. The transformer heats considerably in a few minutes. I had to add ~80 turns to the primary to get ~ 400 mA AC. Victor Koren

[@Schematix]

A microwave oven transformer should never draw 4.5a with no load. Either the primary is shorting (unlikely without you know about it) I'd say running the transformer without a secondary is whats causing the high current draw.

[@supersilve]

I wound transformer small and large. I also tested some of them with only the primary winding without a secondary. The current was only a few milliamps. A microwave oven trafo is designed to work short term a few minutes at a time. The core is also undersized for the wattage it produces thus that is why they force them with magnetic flux making fewer turns to get more power out of them. That explain the extra off load current 3 to 4 amps.

[@andrew_koala2974]

+Schematix Without a secondary winding and also without any load on such secondary winding, what one has is a (resistive load) heater. Some would joke and say 'That's Cool"

[@DCFusor]

These are designed to saturate in normal use, which is why they do, and get hot (also the reason for the shunts). Here in the states, with 120v nominal mains, this happens at 89 volts or so - same deal, you need more turns, or accept the waste and use a fan.

[@T2D.SteveArcs]

NO RUNNING A TRANSFORMER WITHOUT A SECONDARY WHAT ONE HAS IS AN INDUCTOR ( A BALLAST ) OR IF THE PRIMARY HAS ONE OR MORE TAPS A AUTO-TRANSFORMER ....... THESE TRANSFORMERS ARE NOT DESIGNED FOR CONTINUOUS DUTY ......

[@MrBrymstond]

@Schematix How did you manage to get 151 amps off of that gauge of wire? I thought the gauge determines the amperage and I know the device being powered will only draw as much current as needed so how did you manage to tame it down or is that only a open circuit issue with no load? I used a bolt cutter or I've used a large pair of dikes and wire cutters like the one shown in the video and nibble it down the drilled a hole dead center and easily knocked out the secondary, but I didn't get to winding the secondary yet as I am new to this. You should use enamel not lacquer to repair a blunder as all of the magnetic wire I purchased always said enamel, I painted cars for a living . Lacquer eats at enamel, enamel does not eat at lacquer. I should be able to make a center tap out of this, correct?

[@titantitan2851]

Excellent explanation of how to get the voltage required from the mains but what about getting an exact amount of current? Or is that way more complicated.

[@rogerbrowne5514]

How do you get the right current

[@fbw47]

This is a bit late, hopefully you are still monitoring comments: is there a non-destructive way to determine the number of turns on the primary in order to match the secondary to it? I want to wind a 1:1 transformer to use in my shop for isolation. I would use good quality magnet wire of the same size - shouldn't you use proper insulation rather than masking tape? I've seen Nomex paper insulation used before. Wonder where to get that? Nice tutorial.

[@johncoops6897]

This reply is even later 😅 ... The easiest way is to locate two *_identical_* MOTs, and use an angle grinder to cut the 2 welds that hold the top onto the H lamination. Drive the secondary windings out then hammer the primary out of one transformer using wood blocks. Refit both primary windings into one core, then weld the lid back on. .... Things to note: 1. Modern MOTs use aluminium for the primary windings, which needs to be thicker than copper for a given power level. . 2. Microwave transformers are NOT designed for continuous use and have huge power losses (even with no load). This is because of too little steel in the core. So they really are not good for use in proper long term operation. . 3. The secondary of a 1:1 isolated transformer may need more windings that the primary. This is to correct two sets of voltage sag under load. . 4. Almost all MOTs have a primary with the same number of turns as the rated mains line voltage. So a 110V transformer will have 110 turns, a 230V transformer will be the same sized core with 230 turns of thinner wire, etc. . 5. To accurately work out the quantity of turns, wind a test then do math. Start with (say) 20 turns, measure AC Voltage, then divide by 20 to get the resultant "volts per turn". Then finally, wind your calculated quantity on but leave it long until you test voltage again and add/remove as needed to hit your target voltage. . 6. Use an accurate True RMS multimeter. Cheap ones (especiall if not true RMS) will give you strange readings that will skew your calculations.

[@johngeorgio5908]

Dear Sir , may I ask You whether this technique would be appropriate in order to build a same voltage secondary - alas : a isolat transf ?

[@gerryh6795]

Great video. Just wondering what the wattage of the transformer was? I am trying to make a power supply for a 90v / 20 amp DC motor but finding the right combination seems to be a challenge as most of the transformers I have come across are 1100 to 1500 watts power in.

[@moya9450]

This is not practical at all. This transformer gets Extremly hot under normal load. Because the input power is too much. I tried many time in the past to build high current power supply out of it, but no hope. Only you can built Spot welder.

[@dragan3290]

How to work out winding for 14.9 volts as i need to make a simple jumpstarter for 12 volt deep cycle battery? Any reply appreciated thanks from Australia!

[@pulesjet]

Build a Rather Hefty Battery Charger doing this. Was able to start my truck engine using the thing. Did just fine cranking the engine for a few seconds at a time. Any more then that and it would have melted down I'm sure but it worked.

[@garrybrewster5821]

I've only have one creative comment to remove the high voltage secondary instead of distroying it, you may want to use a small grinding wheel to cut along the laminates where it's been tac welded and re-weld this after the re-wiring, just an idea to save time,

[@vassilyknigge850]

Could I use an extension cord for the secondary winding. I have lots of this wire but it has the neutral, hot wire, and ground wire in it. If I just twist these together will it still work fine?

[@packratswhatif.3990]

What was the initial VA rating of the transformer before it was ‘hacked’ ? That way you can figure out the secondary max current for your setup ( assuming proper wire size).

[@MsKermit000]

I saw some people cut the transformer rewiring it and glue it. I copy this and now i got some milli volts only, why this happens? Is it the base i cut or the glue between?

[@kalleklp7291]

Excellent video and very well explained! That was just what I needed..a person that knows what he is doing and not some crappy unsafe shit that sets the thing on fire. Now I know how to build my transformer for my HHO setup which needs 12 VDC.

[@arnoldnazaire6154]

I like to make a 10 ampere 24v, what size of wire will I use for the secondary of the microwave transformer?

[@martinmassinger]

What gauge wire did you use for the secondary winding? I'm in the U.S., which is likely a different standard, but I can figure out the conversion. Thank you!

[@Schematix]

The wire I used works out to be around 12AWG. As long as you buy wire that can handle at least 15~25 amps it should be fine.

[@rdkater]

if you draw 15 amp it will melt thanks to the tick insulation on the secondary get some real transformer wire, look for company's who are rewinding electric motors.

[@albertosequeira8759]

Thanks for the video.How many meters did you use on the secondary, for 12AWG cable ?Thanks in advance.

[@Schematix]

You're welcome, I bought 10 meters and used most of it. Depending on the size of the core, as a guide each turn uses approx 300mm of wire.

[@albertosequeira8759]

Hi again.I just rewind the Transformer, but the core heats up without any load. Whats the reason? Thanks in advance.

[@Schematix]

Most transformers will be warm without any load. In simple terms you have to remember the primary winding is effectively a wire wound resistor between live and neutral and will always use some limited amount of energy even while no load is being drawn on the secondary. How hot the transformer gets does depend on a number of factors. I've got a couple commercially made transformer that easily break into the 50 degrees celsius mark. However If your transformer is too hot to touch there maybe a problem

[@albertosequeira8759]

Yes it might be around 50'c without load. Thanks for the information.

[@babamiyan7443]

I want this

[@leewonnell1192]

What should you actually use this transformer for does it convert everything to 110 or is it 220

[@oddjobbobb]

I’m very late to this party. I hope you might find a moment to answer a question. If you have rubbed the insulation off more than just one of the turns on the primary winding, is there any thing special you have to do to ensure they don’t touch under the lacquer insulation? On rewatching I have a couple more questions: 1. Is there any advantage to making the wooden blocks more of an arc shape so the secondary coil turns are more circular as they pass outside the core from one side to the next? 2. Is the purpose of the shunts to add a ferric (“magnetizable”) spacing between the coils? Or are they there to reduce the air-gap between the coils, getting as much magnetizable material as possible between the coils?

[@thecarl168]

the purpose of the shunt , it change the behaviour of the transformer from a voltage source to a not so good current source , it is needed because the magnetron act as a zener diode , if the shunt were not there hi line voltage ( input voltage ) would destruct the magnetron .

[@oddjobbobb]

@@thecarl168 thank you Carl for that explanation. That is no doubt a very good reason to have the shunt.

[@robertk1117]

All of the information that I have been able to find on rewiring MOT's says to save the primary coil and wind a new secondary. If the primary was not being preserved (because it was aluminum rather than copper) is there any reason to stack the coils as opposed to winding the primary full length (height) of the core and then winding the secondary on top of (over) it as is commonly done in other types of transformers?

[@ProdigalPorcupine]

You can do that, but implementing safe insulation practices becomes a bit more difficult. Also bear in mind that MOTs are wound with the bare minimum number of turns, which means they run close to core saturation so they get hot and draw very high currents when idle, which of course they never are when they’re in a microwave oven. To make an MOT operate like a ‘normal’ transformer, you’ll probably need to double the turns on the primary winding, which doesn’t leave much space for the secondary! They’re far from ideal transformers for most things, but if used for short bursts like in spot welders, they’re fine.

[@robertk1117]

@@ProdigalPorcupine Thank you for the response. I am going to try it and see what I get. I will not be able to double the primary windings but will increase the number of windings to the extent that space allows. It will be a few weeks before I get it done but I will update with the results.

[@ronniepirtlejr2606]

I am just a hobbyist. what are the shunts for? What is the added benefit of replacing them? I heard a engineer say you can leave them out for a 1 to 1 ratio "NOT SO SAFE" isolated Transformer. You will need the added room and the added coupling if doing that . Is there a benefit to putting them back in or leaving them out?

[@jessegresh9043]

Hi Ronnie. The shunts provide an additional magnetic path for the core and limit the total flux passing through the secondary. While used in the microwave, this serves to limit the power going to the magnetron. If you're rewinding the transformer for another application, they can be removed. I recommend high temperature insulated wire for your secondary winding. If you're doing a small number of turns with very large cable, such as for a spot welder, I also recommend FR4 or mica spacers between the turns. MOTs can be very useful and fun but they are very powerful and can be dangerous. Always take extra care and respect them. Take care.

[@BengtRosini13]

so, you rewind the transformer...but can you fast forward the transformer?

[@1959Berre]

Unfortunately, it can not put you on pause, let alone, shut you down. :)

[@randysiemens5491]

I would like to build a 12/24 Volt charger/ jump start for my tractors. Would you be interested in showing how this could be done? Thanks, Randy. We are at -49* below up in Canada right now and always in need of such boosters during winter. They want over a thousand dollars for one. I even have quick connect heat lines between motors but when the batteries are down you’re done.

[@JosephMassimino]

How much current you you get if you wound enough turns for 15 vdc to make a 13.8 vdc power supply?

[@adryanyork3581]

Thanks, awesome vid. Q With the secondary, you did a test of 10 wraps. Did you join those first 10 wraps to make your end result of 20+ wraps? If so how would you do it. Cheers Glad I found your site.

[@Schematix]

Thanks for the feedback. There is no joins in my secondary. It's a continuous length of wire. I tested with 10 turns and left the remaining wire on the spool I was feeding from. That way I didn't have to cut the wire :)

[@adryanyork3581]

Thanks mate, your a natural teacher. Cheers

[@richardworden9747]

very helpful I am an electrician and have 3 microwave Transformers. And was thinking of making a welder. Using number eight stranded silicone coated wire. Any thoughts ? someone told me the wire you wrap around The secondary should be in the same direction as the primary.

[@johncoops6897]

You can't make an Arc welder using a microwave transformer, it won't handle it. You can make a battery nickel strip spot welder using 2, 3 or 4 turns of cable plus a timer trigger module designed for the purpose. . You need bigger than AWG 8 to get decent reliable welds. You might to it with 2 Or 3 parallel connected AWG 8, which will be cheaper and easier to wind than single AWG 4. Check the AWG cross sectional area specs chart. . You will struggle to get a MOT to do sport welds in steel. The main use is for nickel strips under 1.5 mm thick. . The direction of windings only matters if you are connecting more than one transformer in Series or Parallel. If they are out of phase, you got it wrong, so reverse connections on one transformer (You can reverse the primary if you like).

[@harukoyama9515]

DC 0-100V 10A 50A 100A Digital Voltmeter Ammeter Dual LED Amp Volt Meter + Shunt Do you have experience of above meter? Can it be used to measure this AC transformer?

[@gamvin2107]

What is the idle current of this trafo?How fast it going to heat up at light load and maximum load?

[@moya9450]

Very good point. No one pointed it out

[@raeganvallay3465]

Great video. can you use a normal varnish on the coil?

[@srduke]

I've just stripped our old microwave. I'll sell the magnatron on ebay and re-wind the transformer to give an output of around 7V reg/rec down to 5VDC to power the auxiliary circuit on my model railway.

[@thearchitecht2122]

Hi, what happened to the follow-up video with the charger? I had it bookmarked but it's MIA

[@jerrystrader754]

It would be cool to turn this into a bench power supply unit.

[@Bonjour-World]

What is the significance of the shunts? Any advantage or disadvantage to removing them ?

[@awesomeguy9573]

Lewis Balentine Apparently they limit the current drawn from the outlet during idle use and prevent the transformer from overheating

[@Schematix]

The shunts do limit the power to a limited degree. However, without them, most transformers will run much hotter and consume much more power even while idle. I don't really recommend removing them entirely. :)

[@neddyladdy]

Mr Schematix Is there a reason that you used plastic insulted wire rather than enamelled wire ? Thanks.

[@Schematix]

Yes, Pulling solid strand enamelled wire through the transformer would have the risk of scratching off the enamel, Or potentially breaking the wire due to repeated bending.

[@michaeltopping8227]

i have a similar setup for 9v dc using a bridge rectifier. and i cant work out why. when i change the brown and blue AC inputs 240v leads over, i get 4.5v dc output i was expecting there would be no change. any ideas?

[@bowlweevil4161]

what ga of wire in the secondary?

[@jamesfkennedy50]

What would I need to do for 85 volt secondary with a max draw of 135 amps? How would I keep it from overheating? Bigger core with thicker wire?

[@davidb2206]

How did you know it was the secondary coil that needed replacing in the first place? Isn't it possible that the primary would be bad on some discarded microwave ovens? Was the original secondary coil shorted or broken?

[@englishrupe01]

Easy enough to check. First check to make sure there is no ground fault. Then check that there is continuity on the primary. Finally check primary ohms as reference. I am not sure that he was saying that there was anything wrong with his transformer, just that he was illustrating for us how to make our own. Maybe i missed it though.

[@spudpud-T67]

In all household appliances in NZ the primary is going to be 230V. However you will want to customize the secondary to your needs.

[@ozymandiasking173]

What is the load voltage/current for the maximum power output of the rewound transformer?

[@cfresque1168]

There is a lot of aluminum clad 10guage cheaper wire on Ebay, are there any complications with using this wire as opposed to the copper? I am trying to make a 12volt to 120 volt inverter. I am having difficulty finding any solid answers by doing a search. Thanks.

[@makesaveinccomm]

Thanks. you are awsome. I subscrube. you said it clear. one turn is 1 volt. google search said 60 turn for 12 V. so that ways too much. I almost make mistake, lucky I saw your video.

[@KhurramFarooq1982]

hello schematix i want wind a ferroresonant transformer CVT 220 volts using microwave transformer can you help me ????