Building a Spot Welder from a Microwave Transformer!

I think this project may have been on my list since I was in high school: rewiring a microwave oven transformer into a potent spot welder. I came up with an Arduino-controlled system that lets me do everything from tacking shim stock together to welding on nuts and studs. This first part is just the assembly and testing. The next part will be a more detailed look at how I machined the parts. I'll upload all of electrical schematics and code up to my Patreon as a freebie!

[howardtoob]

This is a good video. FINALLY a MOT spot welder video from a common sense individual.
Thanks bro!

[hermanushulsen]

You can control the input voltage with a motor speed controller connected to the primary winding that will give you some control.

[dzozepe]

I also got a stainles steel table. So basically now i have a solid supply of stainles steeel. MAAAAN that got me :D

[nerferfan]

That's sick. The unit looks quite professional.

[TrojanHorse]

Great video & spot welder build, thank you!

[AKAtheA]

FYI you CAN spot weld aluminium if you use a thin piece of steel between it and the electrodes...
Personally I think it might be possible to make this better by using tips with small tungsten carbide insterts on the ends, as it's not a good electrical or thermal conductor (heats up well when current flows through it), but is far more resilient then steel, so it would last a lot longer.

[Demoni]

Great project and video! Having a pneumatic closer would probably help with constancy because of repeatable pressure. I like the little holes on the copper bars, they totally could be used to add extension cables for welding tabs onto lithium batteries.

[amrb]

the Fotek ssr that you use has a ‘zero-crossing detection circuit’. This causes the relay to wait until the current it is controlling reaches zero before shutting off.and similarly wait until the mains voltage crosses zero volts before switching on, therefore you can control the pulse duration of your spot welder only with a resolution of 10mS (assuming 50Hz mains ) - there is no point to set times in resolution of 1mS, the welding pulse can be only whole steps of 10mS . e.g. 10 20 30 40 ... mS etc.

[HuskyMachining]

I have wanted to make one of these for welding thick nickel strips to batteries for making bat packs.... this was helpful... I might need to make a beefier transformer though.... nice video

[murzabaev]

Current on the secondary coil is already limited by the battery cable’s diameter. So thick (more diameter than your battery cable has) copper rails are kind of “overkill”. But in general, good explanation and try. Thanks for sharing your design

[SodiumInteresting]

nice channel name. I'm a new subscriber

im hopefully building one of these with a toroidal transformer. im getting 760amps at 2.7volts from uk 240vac. waiting to fix my lathe so I can get machining things again...

[DeanParmenter]

the best ELI5 of how transformers work.

[dr.romeochair]

Great video! My microwave just died and I'm going to give this a try with the salvaged transformer. I was thinking -- if you attached the heavy leads out closer to the tips, you could get away with just a few inches of copper rod. To get the length of jaws you wanted, you could press fit the copper ends into something like 1" EMT tubing. Your construction looks great, but I'm basically cheap (and copper is pricey). Nice job!

[howardtoob]

Did you remove the shunts? Does removing the shunts do anything more than offer additional room for the secondary?

[bendude]

This is nice, I'd make one but I don't trust myself not to get electrocuted somehow in the process lol!

[Tristoo]

you can regulate the output power a few different ways.
1. take another tap off the transformer from the middle of the 2 windings for half the power (same voltage, same resistance, only the current can change)
2. if you want something more variable you can have an IGBT doing PWM on the input (mains), but gotta be careful cuz you're dealing with AC and transistors don't love that so much
3. you can put more windings on it, which will give you a higher output voltage, but rectify it and PWM it with some nice mosfet(s) at a much higher frequency (few khz maybe), it'll be higher voltage but the duty cycle precision will allow you to just make more or less power overall

and also, be careful with those few millisecond pulse times, you're still getting the same 50/60hz in the output that you get from mains input, which means 20/16.66ms periods. going bellow that will give inconsistent results depending on what part of the wave you end up catching.

also the tabs that connect to the copper rods will likely be the limiting factor on how much current you get since they're likely the more resistive part of the circuit. connecting the copper directly will likely be the wiser solution, or if you have a tig machine just straight welding it.
and after that, the limiting factor will still be the minimum thickness in any part of the circuit (assuming all copper), so rods that big aren't necessary unless your thinnest cable is equally as thick. money would better spent on thinner, longer probes that are more versatile.

great video tho, surely the best I've seen on the topic. cudos!

[davidgoddard]

it all looks great but shouldn't you be concerned about cooling more space is a great way to start with your cooling system then a fan, , really great job thanks for sharing

[harryguy]

How many volts can be expected from one turn of that heavy gauge wire? like 12v?
and would the voltage change with a larger or smaller gauge wire...or does the number of turns determine the voltage?
if so would jamming one turn of the largest gauge wire possible give more amps??
or is it only capable of so much amps and becomes a waste to increase gauge size on the secondary?
Also rather then have the timer could a 12v solenoid be used on the secondary output on one lead just before the tip as a switch? or would it be better to just add a switch to the transformer main?
Thanks for any help...this is all french to me...nice work....

[davidliddelow]

If people don't already know you can get toroidal transformers on ebay fairly cheap, you don't have to sacrifice a microwave.

[qaisarawan]

nice video I tried to follow along with it and 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?