Introduction: How to Make the Metal Melter

In this project you'll learn step by step how to modify a microwave oven transformer into a high-current device that can pump out 800 amps of electrical current.

If you liked the Metal Melter you saw in a previous project, here's how you can make your own!

Step 1: Find an Old Microwave

Picture of Find an Old Microwave

Start by finding an old microwave for free. The bigger, the better.  

You can find them in various places, like on free classified adds, or in your neighbors garbage can, like where I found this one.

Step 2: Harvest the Transformer

Picture of Harvest the Transformer

The transformer is the piece that you'll need, and it looks like this.

CAUTION: Make sure you're familiar with the dangers of opening a microwave, because there are components inside that may still carry a charge and could hurt, or even kill you. Even if the microwave isn't plugged in.

The transformer core is only held together by 2 very thin welds, as seen on the side of this one.

A hacksaw, or angle grinder can be used to cut the weld, then a hammer and chisel used to break it open, giving you access to the primary and secondary coils.

Be very careful taking the primary coil out because you'll need it again. Make sure not to bend, break or scratch it in any way.

NOTE: The secondary coil is harder to get out, and may be damaged by the time you do, but that's ok because we don't need it for this project. However, if you can salvage it intact, it may be a source of thin gauge enameled copper wire for future projects.

Step 3: Re-wind the Coils

Picture of Re-wind the Coils

Ok, your transformer core should now be bare. These are the "E" and "I" sections of the core, and have been scraped with a chisel to remove glue and paper stuck to the insides.

The next step is to carefully replace the primary coil, an ensure it's snug at the bottom of the core. Then add a 5' length of 2 AWG insulated copper cable. This thicker cable will extend the amount of time a massive electrical current can flow before the cable overheats.

The secondary cable is only wrapped 1-3/4 times around the center.

Step 4: Glue It Back Together

Picture of Glue It Back Together

If you don't have a way to weld the base back on, you can use some 2-part epoxy-glue and apply to all the surfaces that will be in contact.

Then clamp it together to let the glue set. I used my bench vise as a clamp and it worked perfectly!

When the glue is dry, your Metal Melter should look similar to this. None of the wires are actually touching each other, but what it can do is very impressive.

Step 5: Melt Some Metal

Picture of Melt Some Metal

The output voltage on this is just barely over 2 volts. But the Amps are closer to 800!!

That's enough current to melt iron nails and steel bolts on contact!

Step 6: Spot Welder

Picture of Spot Welder

I found a practical use for The Metal Melter, in making a Spot Welder like this one. The electrical current can be concentrated to a single point, to fuse thin sheets of metal together. This is known as a "spot weld".

You can see how I made this in a different project.

Step 7: Now You Know!

Picture of Now You Know!

Know you know how to make The Metal Melter!

If you liked this project, perhaps you'll like some of my others. Check them out at


electrofrk made it! (author)2015-08-28

I don't understand how replacing the secondary with fewer turns will step up the voltage. I thought that you need more turns in the secondary. Someone please explain.

LGT300 (author)electrofrk2017-07-29

You are not stepping up voltage. You are stepping up current :)

Jramos89 (author)2016-11-02

I made one and it hums quite a bit and it throws loud sparks instead of turning red hot and melting. Did i do sonething wrong?

Brandonoutdoors (author)2016-10-28

Never mind I got it figured out now ;)

Brandonoutdoors (author)2016-10-28

I made this project and am trying to use it to heat up a heating element but when I clamp my electrodes to my element the electrodes get hot but my element does not. But when I barely touch the electrodes to the element, then it gets hot. What am I doing wrong

ErikG25 (author)2016-03-12

My 600 volt cord says it has max 30amp take 30 amps isn't this going to be an 800 amp project so it's not big enough can you please help I'm standing right here trying to finish and I have different 600 volt wires to work with don't know which one to put on so I can finish this. Please help

Jethrokill made it! (author)2015-12-21

These are scary and LOUD. Dangerous, but fun. I have about 4 MOTs now. Next I want to make a dual transformer welder.

Lugfg001 (author)2015-09-29

兰亭月 (author)2015-07-31


Sir / Madam

I am a Chinese who do not understand English, should not understand English, I rely on translation software, see your article! But there are still a lot of places do not understand! I'd like to see the video! It's a pity that I don't know where to look at the language!

This tool is good, can melt much of the metal?

"I was using the translation software to write, it may make you feel tired! I'm really sorry.

awep (author)2015-06-13

Can if the 2 AWG wire at the top?...

Crazyconnor77 (author)2015-02-25

does it have to be a microwave transformer?

Dan.Broomhead (author)2015-01-14

Question: Why wouldn't you use a cable with a higher ampacity?

2 AWG is only capable of handling 130amps max ( Yet even just using 2/0 AWG bumps your ampacity up to 195amps. Would a cable with a higher ampacity heat up slower during use than one with a lower rating? I'm just trying to learn as much as I can before making one of these. I'm also trying to make it usable for longer periods and possibly larger items, or sections of larger items. I'm a hobbyist blacksmith and this would be awesome to use if it could be modified somehow for forging.

avocadostains made it! (author)2014-10-29

I just made this. Is it supposed to be really loud? Sort of like a hairclipper? Anyways a few tips for anyone who tries this: 1.A grinder makes this project way easier, grind out the welds that hold the E part of the transformer on, then knock it a bit and it will come off. 2. Also a grinder makes it a lot easier to get the unused coil with all th wraps of little wire out. Just grind through it a bit and then pull out some strands till it gets loose. 3.You're probably going to mess the coils up up doing this so wrap up the ends of the coil you want to keep with tape or something to protect them from getting little bare wire spots. 4. Get more feet of 2 gauge cable. Get like 10 ft. I used 6 feet and the cable ends ended up a bit short. 5.Wear some dark sunglasses or better a welding mask when you try this out. It's real bright the sparks. 6.I used wire tires/zipties to hold it back together after reading that somebody used a hose clamp. The zip ties didnt work great, I couldnt get them tight enough. Do get an appropriate size hose clamp or better a couple. All in all awesome project! Havent figured out much use for it yet. I'm thinking welding. I'll try the spot welding instructables next. Theres also one called 'welding for punks' that seems to use this approach. Thanks King of Random!

Actually just use big hefty zip ties to hold it back together and make a slot for them to go through so they wont move around. Works great.

shane.amy.5 (author)2014-08-24

wait i thought that amps or current were what killed and not the volts because from what I've heard even 2 amps is enough to kill a person..... or was the information wrong? And it doesnt need to be plugged in or anything?

Davin-Cheap (author)shane.amy.52014-10-09

5mA is enough to kill depending on personal resistance and how it goes through your body, this is a high risk project b advised

Shortcircui (author)shane.amy.52014-08-27

he volts need to be sufficiently high to pass through the skin. so in truth, volts can contribute to wether you are roasted or not. and these high voltage devices often have capacitors that can store a charge and potentially kill you

veinha (author)2012-12-16

how up the voltage to 12V?

More turns of wire on the secondary coil. Probably about 11-12 turns would do it, but you'll have less amperage as a result.

can u cut the plug for the microwave and attach a nail and use that instead?

KarenH1 (author)2014-08-05

My son made this and it makes a loud humming noise that is scary! Is it supposed to do that?

jmurray33 (author)2014-06-01

hey! i just took the primary coil out of my transformer and scratched it a bit ( it was glued in pretty strong) and some of the paper wraping ripped a bit. i was wondering if i just needed to get another transformer or if it would work just the same?

I_StarkGuy (author)2014-02-05

I just finished mine!!!!! Moving on to the spot welder!!

Benjamick (author)2014-02-03

Oh your Majesty, King of the Random, i have a question: i need a 6V DC transformer that puts out at least 1360mA. I didn't feel like looking all over for it, so i looked around what I had, and found a 300mA 6V DC transformer. Is there any way to modify it and make it put out 1.36A or more ?

ccrome (author)2013-10-02

Heh, my microwave pooped out, so I just built the metal melter. Awesome! I used #4 welding wire from a welding supply store. That stuff is super supple and flexible. Very nice cable.

Also, the #4 wire allows me to wind anywhere from 1 to 2.5 coils on the secondary WITHOUT disassembly! It nicely just scoots through the slots. If I have something a little higher resistance, I just increase the output voltage by winding another loop!

I love your videos! I think I'm gonna have to go get a projection TV now too...

connorACIII (author)2013-07-30

I found some 2 awg cable at Lowes but it's not pliable at all. are you sure thats the right stuff?

pwnag3 (author)2012-12-13

Don't weld it even if you can, transformer iron (silicon iron) spits like crazy when welded
(i speak from experience), also it may melt the insulation.

Thanks for the tip! How do you suppose they weld it in the first place? It would be good to have a solid connection to help reduce noise from vibration in some cases.

Looking at the weld, I would say TIG or PLASMA at 100-150 amps, 30" per minute travel, argon gas shield, in an automated machine, although you could do it by hand with these parameters.

Thanks for your reply! It's impressive you can tell that by looking at the weld .. must come from experience? What do you do? I don't suppose you could do it with a stick welder could you?

You could but it makes a need intense pinpoint heat with a good inert gas shield...notice the weld is about 1/8" wide and 1/8" deep with little heat mark beyond the edge of the weld, that indicates high travel rate. You might also use a CO2 laser in an inert atmosphere.
25 years ago I designed servo controlled welding systems for defence contractors.

Spot on! Especially the part about high traverse rate. If you try it with TIG I would suggest submerging it to the top of the winding to heat sink the unit. Ya gotta be a little creative for this...

wire feed (MIG) welder; grind the area to be welded to free it of silicone. MIG is fast enough to prevent heat buildup

you could try a large stainless steel hose clamp around the out side to stop vibration. i have an old microwave, and need of a spot welder. i think i'll try that when i see if i can make one. thanks for the idea.

Excellent suggestion. Thank you for the idea as well, and best of luck!

I tried welding one together with FCAW. the laminations popped, everywhere, and my wire insulation caught fire

pwnag3 (author)pwnag32012-12-19

Although you COULD do some tack welds without much worry just set up some sort of shielding so sparks don't hit the wires

rat terminator (author)2013-07-17

"submit" does not appear under the challenge

zacker (author)2012-12-14

how is it, you can touch both ends of your cables and not get zapped but when you touch them to a nail, it melts it? is it because the current flows through the metal faster than a human? or is it something to do with resistance?

It's Ohm's law. V=I*R. In this case 2 volts = (unknown current)*(resistance of my body).

The resistance of the body changes constantly, and depends on moisture and many other things, however I usually measure in the multi mega-ohm range, which puts the current (if any) in the less than 1 micro-amp range. It would take 100 Milli-amps to stop my heart .. and that's about a hundred thousand times more current than what would be flowing through me.

However, metal is millions times more conductive than me so can allow the full potential of the current to flow .. so in that case we can have around 800 amps flowing through the metal.

Does that make sense?

It's not about the current, it's about the voltage. Everything conducts electricity, even things that are used as insulators, you just have to get the voltage high enough. Dry skin doesn't conduct electricity until you have upwards of 1000's of volts. Once you reach the threshold for conductance, current will flow and you will have a shock. This is why stun guns and tasers are such a high voltage.

You are correct though in that it's the resistance of the human body that keeps us from getting the shock. It is what requires the voltage to be so high.

I see what you're saying, but it is about both voltage and current, because they work together.

The thing is, if the voltage isn't high enough, there will be no current flow. While current is what will hurt you, it's flow won't exist unless the voltage is high enough to overcome the resistance of your skin.

Yep, exactly. Wasn't that the reply I gave to sacker?

Well, kind of, except you never stated that it was the low voltage that made it safe. This had to be inferred from what you said, which is why I clarified with my post.

You're right in all of the above! Thank you for your clarification :)

yeah... its sorta what i thought... i just had it backwards, I thought it was because the metal had more resistance than the body so more amps would be sorta backed up instead of going right in and well, that explains it. thanks!

BTW, Im the one on you tube this AM with the bottle cap

Oh yeah, sweet. Thanks for all your comments!

no prob, thanks for all the cool posts... gonna possibly mess with my 55" fresnel this weekend.. see how that goes.

About This Instructable




Bio: Random Weekend Projects
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