DIY Spot Welder

DIY spot welder


In this post, I will show you the spot welder I made. A spot welder is a very useful tool that can weld two pieces of metal by simply pressing them together and passing a high current through that small point. This causes that particular spot where the metals are pressed together to heat up sufficiently to melt and fuse them together.

Many products like battery packs, kitchen utensils, appliances, cars, … use this assembly technique as it’s a quick and easy way to make make a mechanical connection that doesn’t require any extra material like screws, nuts, or bolts.

For me this spot welder will be useful for future projects like making baterry packs and repairing things.

Hardware used:

Making It

Here’s the schematic. The red board allows you to set the power and length of pulse used to make a spot weld. I’ve seen a lot of people use an Arduino and an SSR(solid state reality) to do this but I decided I’ll just buy this board as it’s quite cheap and has all the functionality I need including a display.
Most commonly people use a microwave oven transformer to make a spot welder but I used an old transformer I had lying around. I took out the secondary winding and replaced it with a few turns of a thick welding cable. I probably should have made one less turn and had the wire come out at the bottom.  Oh well… now it is already mounted on the board now and I don’t feel like disassembling it all.
I mounted everything on a piece of wood I painted black and installed some rubber feet on. I 3D printed an enclosure for the electronics.
Next, I wired it all up. The wiring it’s quite simple. Most of the wires are just extensions for the LEDs and potentiometers enabling them to be mounted onto the case. The same goes for the trigger which is connected to the banana plug mounted on the side of the case.
Final result.
Additionaly I made two adapters using a copper clad PCB. This way smaller probes can be used for spot welding li-ion battery packs.
If you are spot welding two pieces of metal together it can be tricky to manually position the tips properly and apply enough pressure. That’s why I also made this pneumatically powered clamp.
This thing could really use some improvements like better mounting points for the spot welding tips, better mounting points for the piston, and a better hind for the clamp. But it does work and I don’t plan on using it that much anyway.

It’s operated by a foot switch that triggers an atttiny mcu. The attiny activates the air valve by using a relay. The piston then closes the clamp and waits for a second or two before triggering the spot welder via the second relay. If you would like to know more about programming the atttiny you can check out these two posts I made: Attiny45 and Attiny85 Digispark Board. 

For the pneumatics I’m using the air compressor I made in this post for the air supply. I put a spring on the piston and a valve on the air exhaust to soften the hit when the piston reaches its final position. I also added a pressure regulator on the input to adjust the for of the piston/clamp.
The electronics before I covered them with a 3D printed cover.
Here’s the very simple code for the mcu:
const byte inputSignal = 0;
const byte airValve = 1;
const byte spotWelder = 2;

void setup()
  pinMode(inputSignal, INPUT);  
  pinMode(airValve, OUTPUT);  
  pinMode(spotWelder, OUTPUT);  

void loop()
  if(digitalRead(inputSignal) == HIGH){
    //delay(250); //Simple debounce. //Uncomment if debounce capacitor(C2 in schematic) is not used on the input.
    if(digitalRead(inputSignal) == HIGH){
      digitalWrite(airValve, LOW);
      digitalWrite(spotWelder, LOW);


      digitalWrite(airValve, HIGH);
      digitalWrite(spotWelder, HIGH);



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