Fritz had me remove the 22v zener in the over voltage protection circuit. The cap was then able to charge to 20 volts. It did work very hard from 18 to 20v however. Q4 that drives the charging, was working far harder than usual. So I put the 22v zener back on the board. It seems that the zener limited the cap’s voltage to a perfect level. The zener has a suffix on the part number that shows it’s actually a 20.5v zener. Each voltage has 4 different levels. Mine was the lowest end of the 22v range. Fritz said I needed a full 3 farad cap in order to get to 20v. Mine only tested to 1.6 farad. It’s an audio cap rated at 4.0 farad. Why is it that audio stuff is always playing a numbers game with their ratings?

So now I have some new lower value resistors that I’ve tested on the discharge side of the spot welder. I really like the responsiveness of these resistors. But the voltage regulation has become twitchy. A bunch of mounting and fabrication of parts is all that hold back getting this spot welder finished.

Also ordered a foot switch recommended by Fritz.