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On Tue, Apr 15, 2025 at 06:53 AM, Tony Casey wrote:

... Normally, unless otherwise specified, Rpar = ∞ in capacitors. This shouldn't be affected by the Gmin setting, because Gmin is only placed across junctions. The option for placing a conductance between each node is Gshunt. The default for Gshunt is zero.

I think that is not quite true, but it is one of those "surprises" that you may not have realized was there.

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The LTwiki () says that there is a non-zero conductance across capacitors, with the name GFARAD and value GFARAD*C, and that the default GFARAD is 1e-12 Siement/farad which happens to equal GMIN.? The Help page for .OPTIONS says the same.? In any event, you do have the ability to controls the parallel conductance across your capacitors:

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? ? .OPTIONS GFARAD=0? ?; disables it

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The Help page says that the default GFARAD is 1e-12 and not GMIN, but I wonder if its default value is really GMIN.? Note that their units are not the same (one is Siemens and the other is Siemens/farad) even though their values are the same.

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In addition, depending on how you connected your series LC circuits, it's possible that you created floating nodes with no DC path to ground.? For example, a series LC trap with one C is probably OK but if it had two C's in series, it has a floating node where the capacitors join, and LTspice "fixes" that user-mistake by adding a GFLOAT conductance there.? That might be in addition to the GFARAD*C conductance, but LTspice might combine the two instead of giving you GMIN + GFARAD*C.

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GSHUNT is yet another thing, independent of all the above.

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If the log file pops ups every time, it means you have warnings or errors. At least that is the case with 24.0.12 or 24.1.4. I haven't moved on yet.

Yes, and I don't think that can be disabled, except by eliminating all errors and warnings.

I actually checked this before I wrote the message. I had a schematic with just a default 100pF capacitor grounded at one end. I set the? initial conditions as IC=10.

I ran:

.TRAN 0 6000 0 10m

..and the capacitor voltage at the end was still exactly 10V.

I got the same result in 17.1.15, 24.0.12 and 24.1.4.

From that I concluded there was no shunt resistor, unless explicitly specified.

However, I just checked again, and adding numdgt=15 revealed ~62nV discharge at 6ks. Then adding GFARAD=0 eliminated this discharge. 62nV is less than the single precision resolution at 10V, so it would not normally be seen. With GFARAD=0 and with a 1e10T shunt resistor, the discharge again was ~62nV.

So, I concede LTwiki and the Help are correct.