Problems with simulating a super simple circuit. Where am I wrong?

Schematic Simulation (Ngspice)
1

I’m trying to simulate a TRIAC circuit that is super-simple, but it refuses to converge.
Here are the relevant files:
Softstart_2_triac_sim_exp.kicad_pro (6.2 KB)
Softstart_2_triac_sim_exp.kicad_sch (14.8 KB)
st_standard_snubberless_triacs.lib (33.2 KB)
Sim params: transient, 20u, 50m.
The odd thing is, that I’m using the same TRIAC in a more complex circuit already, where it simulates beautifully.
I’m stumped.
Any ideas?

Thanks.

2

I cannot comment too much as I have never tried Spice via KiCad.

But it looks to me like the triac in this circuit would be turned on 99.9% (not a calculated number) of the time.

There are some thyristor circuits which can behave in a “chaotic” manner but I do not think that is the case here.

3

Adding
.options chgtol=1e-10 reltol=0.01
into a text box on the Eeschema canvas may help during high voltage simulation by relaxing some internal simulation conditions.

4

WOW!
That worked.

Thanks, @holger.

5

You’re absolutely right, it’s a simple on/off mains switch. But it’s a part of a larger circuit that I can’t get to simulate, so I’m simulating each element separately to find out where the problem is.
This was one of the problems, and holger’s solution worked. But leaves open the question: how on earth is a normal user to know this?

6

Welcome to the world of SPICE… its a dark scary world of “hacks” to make an imperfect representation of the real world give the appearance of working.

Relaxing the convergence tolerance is one of the known solutions and the other is placing high impedance resistors ( >10M) to gnd or across devices that cause this type of issue.

7

Tightening your .options:

To:
.options chgtol=1e-12 reltol=0.005

Also works. It seems to be very marginal.

UPDATE: adding these options make the simulations on the more complex circuit look way off.
And the total circuit simulation still doesn’t work. The errors seem random, pointing to different nodes whenever I change the schematic value a little bit.
Perhaps I need to try my luck with LTSPICE.