PIC controlled spot welder
PIC Controlled Spot Welder schematic

This circuit pulses half cycles of AC current into the primary of a transformer which has had its secondary removed and replaced with a few, really thick turns.  The PIC controls an opto coupled triac which then triggers a power triac connected between the primary AC power and the transformer primary.  With the keypad, custom heat cycles can be programmed and then with the press of the "fire" button (Or foot switch) applied to the work piece:  ((h x 8.33ms) + (r x 8.33ms)) x p.  The time unit is 8.33ms because all timing is based on the line frequency x 2.  h=heating, r=resting, p=pulses.  I have melted tungsten rods in half with no problem with this unit.  Releasing the "fire" button in the middle of a heat cycle terminates the cycle.  The firmware was done in PIC ASM, and only far enough to do the job it was built for (Welding tabs onto batteries).  The plan was to be able to enter in and save complex profiles etc.  I suggest the APT1211 optocoupler and Q2008L4 alternistor to drive the transformer primary and provide PIC to mains isolation.  Gerber Data / Firmware

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This page last updated on June 28, 2009