When i wanted to continue with the zero cross detector and a triac i quickly realized that the zero crossing was not detected well enough. So i search in the net and found another circuit on https://www.dextrel.net/design-ideas-2/mains-zero-crossing-detector.html (08.06.2020). I altered the circuit a little bit (see schematic) and checked the signal with the oszilloscope.
Perfect! With the triac circuit below i am now able to dim a light bulb or some other resistive load.
The next step would be to design a printed circuit board – or to buy the almost same controller circuit board on aliexpress, with two poti, a stm microcontroller (STM8S003F3P6), a seven-segment display, a really powerfull triac (BTA100): The NY-D01 Board.
With the two potentiometer you can adjust the welding time in 20 ms steps (full sine wave) and the power between 30 and 99% (dimmer). An old 9 volt transformator, a foot switch and electrodes from ebay and i start welding the first lithium cells.
For the board is also a fitting frontpanel available which i have ordered on aliexpress (not yet delivered…). Connectors for the electrodes are also ordered.