[Archive] Definition of the electrical circuit

Message by Alessandro Vicini:
I am using the “voltage generator” (V) connection to establish desired potential differences between spacecraft ground and other nodes (solar panel cells).
Anyway, in the surface potential distribution of the solution I don’t find the same potential differences that I imposed.
Am I getting something wrong? Thank you.

Message by Alessandro Vicini:
Ok, I verified that the imposed potential differences are mantained if the node is connected to a conductive surface, while they are not if the surface is a dielectric (in the latter case I don’t understand how it works, though…).

Message by Guillaume Tcherniatinsky:
The surface potential distribution you can visualize in post-processing is actually not the potential of super-nodes (between which you define electrical circuit by hand) but the potential of nodes. A node is automatically associated to each triangle of the surface mesh. For dielectric materials, nodes are connected to their super-node through a capacitor and a resistor in parallel and connected with neighboring nodes through another resistor. They receive current from the plasma as well. The values for resistors and capacitors are calculated from the characteristic of your dielectric material (resistivity, dielectric constant, surface resistance) and from the local characteristic material thickness in the property “Macroscopic characteristics”. The solver then computes the variation of V on the nodes using potentials at associated super node by solving the circuit.
For conductive surfaces, the resistor and capacitor in parallel are replaced by a simple wire, so in that case they have exactly the potential of their associated super node. This model is used when your material’s conductivity is set negative, though I wonder if there can be a global parameter that overcomes that local parameter. I have not tested global parameters Surface interactions/surfaceConductivity Surface interactions/volumeConductivity but I understood that they should allow to choose if you want to take your materials into account or not.
The documentation that describes how it works is quite hard to find: In help menu, click on Circuit Solver in SPIS-NUM technical notes. It opens a page where the first link is “spacecraft equivalent circuit”. Click on this link and you are in the right page. (path spis_root_directory/documentation/DocSpisNum/HowTo/Spacecraft circuit).

Message by Alessandro Vicini:
Thank you Guillaume, now the picture is clearer.