extreme convergence error

What exactly do you mean by “convergence error”? And, as long as there is no “cannot find solution” at startup, the capacitor coupled ground is unnecessary. In this case, the capacitor coupled ground is the source of a problem, probably the problem your talking about. This is because ALL wires to ground have to go to the capacitor coupled ground, not true ground, because otherwise it will mess up the capacitor coupled ground bad. Also, there can’t be any op-amps with their outputs feeding into the capacitor coupled ground grounded circuit because that will also mess it up bad. If the output of the op-amp was feeding into a different circuit with regular grounds only and the only thing connecting the two circuits are op-amps, transformers, and CCVS/VCVS/CCCS/VCCS (current controlled voltage source/voltage controlled voltage source/etc.) then it will be fine. This is because they provide galvanic separation (assuming the two sides aren’t connected by non galvanic separation means). Even the op-amp works, since it just acts as a comparator and as long as the output doesn’t feed into it’s input with non galvanic separation no issues will be generated.

You can remove the relay and leave the ground switch closed upon startup, and it will work fine. The problem should be because the resistor at the top-right is connected to true ground, and any current that flows through it flows through the ground capacitor developing a charge on it, which messes up the op-amp because its other input is connected to true ground, not the capacitor coupled ground.

Btw, when I mentioned that op-amps were galvanic separators, that only applies in this simulator. Same goes for CCVS/VCVS/CCCS/VCCS unless they like optocouplers or something.

"Convergence error" is what all the long-time users here call "cannot find solution" to confuse the new guys. :)

as for the rest... all i can say is, "derrrrrp! i knew that. i used to know that..." lol

Capacitor coupled ground doesn’t remove “cannot find solution” if there is some part of the circuit connected to a regular ground including the internal ground in an OP-amp. Also, when does the “cannot find solution”? Capacitor coupled ground only helps with “cannot find solution” at startup, not at any time in the circuit’s running period.

Yup.