Resistance in simulation

[coop]

Why is it that when I add a resistance to the sim sometimes I get a positive current through the resistance and sometimes a negative current even when the circuit is only 1 dc voltage and 1 resistance. Does the resistance direction change with it orientation.

[marcos.uniovi]

Yes, resistances do have a polarity for the sensing of the current, even though this polarity is not shown in the drawing. If you get a negative current with respect to the one you expect, just rotate the resistor and run the simulation again.
Same thing happens with caps, inductors without dots, etc.
If you want to see the current with the correct direction you can add a 0V voltage source in series. In a voltage source the current is always measured going into the positive terminal.
Or you can visit this library: website/Qspice at main · marcosalonsoelectronics/website · GitHub
and download the isense device to measure currents.

[KSKelvin]

More information for your reference, including how to identify pin order from GUI.

The order matters (or not?)

The +ve current direction in spice for resistor, capacitor, inductor and voltage/current source are defined from 1st net to 2nd net. There is no default order, it is just because you used Ctrl-R to rotate Rc, and in schematic, its 1nd net go to bottom in your schematic. You can check net order by F3 (View Symbol Properties) Click on component Goto Pin Nets Click pin name you want to highlight [image]