Arduino ATmega328p 18650 Spot Welder



Introduction: Arduino ATmega328p 18650 Spot Welder

A Microcontroller built on the ATMEL ATmega328 chip. This controls how long the weld is done. The weld time are measured in milliseconds. When spot welding it is common as well as important that there be two welds, Why ? because the first weld clears the strip of all impurities that maybe stuck to it after production. The Second weld is when the strips melt and gets welded to the cell. The chip is powered by a regulated 5v supply from an on-board PCB transformer. The PCB works only on 240VAC, the Transformer can be replaced with a suitable 120VAC for the PCB to work in countries with 120VAC. Updater version, new design.


  1. Surge Protection
  2. Inbuilt Power Supply
  3. Dual Pulse Welding
  4. Dual Surge protection
  5. Thermal fuse at the secondary
  6. ZeroCross Peak detection
  7. Variable timed pulse (indicated by LED from 100ms to 450ms)
  8. Dual function weld
  9. Manual Weld and Continuous Weld (upon holding weld button for more than 800ms)
  10. TVS protection diode at the dc side
  11. Snubber Circuit
  12. TRIAC to control AC load
  13. Audible Weld alert

More Info on this project Working of the finished PCB.

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Step 1: The Assembled PCB

These days anybody can solder a PCB. Not very hard to learn either Grab the components from here. Always insert the ATMega chip at the end. Power up the PCB and if you see th POWER light lit, then GOOD JOB, you successfully soldered. Now you can insert the ATMega Chip.

Step 2: Scopview

Readings from the Oscilloscope shows how the whole PCB works or rather how this is designed to work, This PCB is designed to only switch on at the PEAK of the sine wave, shown here as the blue wave. The MOT, aka; Microwave Oven Transformer. Since the MOT is HIGHLY inductive, it is very important that it should be switched on at the MOT and not at the zero cross.

Channel 3 in pink color shows the triggered pulse makes strip hot for the second weld. The second weld is the actual weld.

Channel 2 is a secondary reference for the zero crossing. The zero crossing gets pulse from the H11AA1 optocoupler and sends a signal to AVR to trigger the TRIAC at every zero-cossing.

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