DIY Spot Welder From Microwave - Now With OLED Display!

Intro: DIY Spot Welder From Microwave - Now With OLED Display!

This project is an outline of how to build a resistance spot welder using salvaged parts from an old microwave. Im using it to weld nickel tabs onto 18650 battery cells but depending on how you position the arms it can be used to weld sheet metal and other metals objects. Lets get welding!

STEP 1: Salvage the Microwave

Quick note of caution!

The inside of the microwave is quite dangerous. The large capacitor maybe charged and can deliver a nasty or even fatal shock so ensure you discharge as soon as possible by touching a metal rod such as a screwdriver across the terminals to discharge it.

Okay so open up the microwave casing to reveal the electronic bits. Discharge that capacitor and get to work on removing the parts. You should find the transformer which should look very similar to the one in the photos. Remove the nuts and it should slide out pretty easily. I salvaged a few limit switches that we will use later and some of the cables are handy for power connections.

STEP 2: Remove the Secondary Coil

We are going to rewind the secondary coil of the transformer as we want more amps and less volts. The primary is where the mains power is attached and the secondary has finer wire windings with the red wires attached.

The fewer turns of wire increase the amps but lowers the voltage, and more turns increase volts while reducing the amps. We don't need the secondary coil so it can be removed either by cutting off or by grinding the weld on the transformer body and sliding it out. Be careful not to damage the primary coil as we will be keeping this.

STEP 3: Add the New Winding

The new winding will provide the current needed to weld stuff. By using really thick cable we can reduce the thousands of windings to a couple which will provide loads of amps. The thick cable is needed as the resistance will cause it to heat up and melt the insulation if its too thin. Not good!

The primary coil is put in first followed by the 2 shunts either side and finally the low gauge wire (blue cable) is wrapped a couple of turns. Remember to leave a decent length of cable that will attach to the welding electrodes.

STEP 4: Finish the Transformer

Our super high powered transformer is nearly complete. We just need to weld the top back on to seal it up. You could alternatively use 2 part epoxy to stick it on. Options are good, pick whichever one is easiest for you. :)

STEP 5: Electrode Terminals

We now need to attach our cable ends to the copper pins which we will use to weld. I machined some copper terminals but you could use some copper clamps from the hardware store. I've also attached the CAD file for the electrode clamp that I made. Here's the Fusion360 link too. http://a360.co/1Loyh1j

STEP 6: Welding Arm

I'm using this to weld nickel tabbing to battery cells so I've positioned the two welding electrodes side by side although you can easily mount them opposing like a traditional machine. I designed and laser cut a simple MDF case for the arm which houses the switch for operation and holds the electrode terminals.

STEP 7: Package It Up

There is 230v of dangerous electricity coming into the transformer so its important that its covered. This laser cut case should do the job pretty well. Just make sure everything is contained as it will also look much better as well as being safe. Bonus!

As for wiring its pretty simple. Just connect the live and neutral to the transformer primary using the existing spade terminals, I would recommend adding a switch in between one of the power cables to make it easy to turn on and off. I salvaged this one from the microwave.

Thats it we're done! Have fun with your new spot welder!

STEP 8: Add an OLED Display & Pulse Control

Add this circuit for precise control of the duration of the weld pulse. Very handy for welding 18650 cells and other thin metals.

The duration is varied using a potentiometer and the duration is displayed on the OLED display in milliseconds the coil of the transformer is connected inline with the SSR.

Build up the circuit on a breadboard and then transfer it to some perfboard when you've got it working. The big red button can be replaced with a simple foot switch if preferred.

I installed my board and SSR on top of the transformer, remember to add some insulation between the metal transformer body and the circuit board to prevent shorts.

You may need to add a 5v source for the Arduino as the SSR can draw a modest amount of power, I just cracked open an old 5v phone charger and connected the 5v output to VIN and GND on the Arduino.

Comments

[frizzo144]

What do you think about controlling power to this using a motor speed controller like you could use to slow down a drill? just to the primary, not the arduino wall wart or anything else.

[matthyewww]

Can you please explain the copper coiling inside the box directly behind the electrode pivot

What arethey for?
What is wired to that?

Could you please provide a wiring schematic or basic drawing of wiring .
That would be very much appreciated!

[carlsandra2005]

Looks like that is just pins to hold laser cut parts together, they connect to nothing
POT 10K GND. A0, 5V
potPin = 0; // A0 Middle analog pin used to connect the potentiometer
Button 5V , D2 + 500 ohm resister to Ground

inPin = 2; // Button 5V and D2
ssrPin = 3; // SS Relay D3

Oled Gnd, 5V, Sda A4 SDL A5

[isaacacheampong]

I'm interested in making one of these but the main snag is the cost of the thick copper wire to wind around the transformer. I've tried and it's never cheap. All I can find is standard gauge wire, so I may as well but a second hand arc welder. So I was thinking of alternatives; would slicing copper tubes used in plumbing work? They're relatively easy to find. The idea is to cut it along its length, flatten it, cut it into slices to make it more like wire, wrap the cut pieces of 'wire' in masking or insulation tape.... you get the picture! Would this work? Is the electrical conductivity of copper pipe the same as copper wire...??.etc etc

[mickeypop]

look in your area for a metal recycler.
you can find microwaves there as well as cable

i bought 15ft of welding cable for just $5
they will usually sell by the LB and because the insulation means mixed materials it is really cheap

NOTE; welding cable is quite flexible by comparrision because it typically has 500 strands instead of 7 so it is not stiff

i have made 2 spot welders this way, 1 for LI batteries and 1 for steel plates.

[MikeD50]

use a car starting jumper cable … cheap and well obtainable

[isaacacheampong]

Thank you!

[isaacacheampong]

Thanks for the suggestion!

[flyboydaddy72]

I have been wanting to make one of these for years. I understood most of your project but if I have a question is it OK to ask? Nice project and Thank you,
Kevin

[Skelecorn]

😳🙌🏻wait! 🤔A picture of the capacitor 👀 for easy reference🧠 to the 🤓 person whom is unfamiliar with the thing 😵 might probably not be a bad idea 😎so that avoiding and rectifying the potential hazards ☠️ (before accidentally injuring oneself!😱🤕) can occur successfully.🤗😁💚💙💜✌🏻👌🏻🤙🏻🖖🏻 👍🏻

[rajesh shelke]

sir, can you post the arduino code program of battery weld controller. i am stuck up with this project using arduino uno, oled, display, encoder switch for changing variables

[AdrianI22]

Hey man!! Great work you did here!! I like it and i am trying to make one myself but im having problems with Arduino programing. The u8 lib you are using is not working and i have read that it got an update. Anyway, if i put the code to read the triggerSwitch in the void loop() my relay blinks endlessly and it shuts down my dysplay.
Can you help me with the programing? Or anyone who is better at this? I am not a programmer and this is my second week i am trying to understand code.
Thanks!!

[candellightpoet]

what awg gauge of wire is the blue wire

[rosekreuze]

hi. great tutorial! but i dont have transformers salvagable from an old microwave, however i found one online which are cheap. but i have doubts that they are might underrated. could you give what are your thoughts about my attached screenshot?

[ChrisW545]

This looks great - I will build it. Thanks. Two questions about SSRs though:

1. SSRs do zero-cross switching, meaning they only turn on when the mains goes through zero volts. This means your timer will not be accurate because it will not come on when you close the switch, it will come on at the next mains zero crossing after you close the switch. It crosses zero twice per cycle - i.e once every 30mS if you run 60Hz or 25mS for 50Hz. Is this level of consistency an issue?

2. SSRs, I'm told, have a problem with highly reactive loads - which this transformer is. They are likely to fail early. Please tell me how many welds yours has done. If it's hundreds, then maybe it's not much of an issue after all.

Thanks again, Chris

[sdtrent]

Pinging an old thread here. AC output SSRs are available with zero-cross and non-zero-cross outputs. The one shown in the images above, the SSR-25 DA, appears to be a non-zero-cross type that has the ability to provide less than full half-wave power to the load. This is done by turning detecting the zero-crossing of the input power and turning the SSR on after a precise delay. Of course driving an inductive load, particularly with a steel core, can make the relationship between the turn-on delay and power delivered to the load. Some SSR are specifically rated to handle inductive loads (SSRs not rated for inductive loads can fail to self-commutate meaning they might turn on and never turn off because they begin self triggering).

[garzo]

Maybe it's quite late for an answer but yes, the timer can't be regulated in smaller step than the 20mS for 50Hz and 16.7mS for 60Hz (check your numbers). Anyway i don't feel this a an issue. Can't answer question nr. 2.

[adybulborea]

Thank you very much . Very nice progect. Can you post schematic for connections?

[wrsexton]

Excellent tutorial! I have finally learned why people change the windings in the transformer.

Could you provide a bit more detail about how you attached your cables and electrodes to the electrode terminals? I'm a little confused on that.

[DuckTurd]

I have provided a photo of one of my electrodes, it consists of #6 bare copper ground wire as the actual electrode, a medium sized grounding clamp with a
3/8 bolt hole, a brass battery bolt extender and a #1-2 cable ring loop connector. I'm using two pieces of 3/4 EMT conduit 18 inch long for my electrode arms. The #2 wire will travel up the center of each arm connecting to the ring loop connector either via crimp or soldered on, most likely crimped. Then I'll use a piece of silicone impregnated shrink tube over the wire & ring loop connector and brass battery bolt extender, slide it all into the pipe and J B weld into place. That's how I'm making my electrode set up. They're all different, it just depends how much trouble
you want to go to as far detail.
I want my wire conductors to be hidden so I figured out a way to run them in the center of the pipes. Good luck with yours.