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LTspice polarise resistor shock
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robint:
I am now revisiting the LTS tool for a little potboiler of mine and see that the latest ver (from LTS IV)  is now jumped to LTS 7.  I am having to relearn here so its a bit of a slog.  FWIW its an indispensable tool and forces design thinking rather than the dirty suck-it-and-see approach by rank amateurs. 
I hope Im in the right place for my discussion here - pls mods re-direct as necessary as there's no obvious forum category here.

enough intro

There are many little quirks and inherent bugs? to learn workarounds which LTS users are fully aware.

One that completely floored me was that resistor models have an inherent POLARITY.  Fell off my stool back then.  In a word it makes a difference which way round you insert the resistor to your circuit - just like a battery.  GO FIGURE :P :-DD

Sadly there is no obvious tag to show polarity on the schematic or any dropdown info (like +/-).  This can so easily catch you out especially if its not obvious which polarity you have with applied voltage - like a wheatstone bridge type cct)

I have a simple solution, but its so obvious that the 10^6 users over 20 years must have thought of it.  It involve putting a simple dot on the symbol to show positive end.  I can post the trivial .asc file here to help anyone else but I fear that there must be a fatal flaw to such a simple method.

Would any experiences users here please deflate my hypothesis - its bothering me.





Zero999:
SPICE is just a glorified calculator. All currents and voltages are differential, thus have a sign, so every component has a positive and negative terminal. Normally it doesn't make any difference, but seeing a negative current when one would normally expect it to be positive is a bit confusing. I agree, it would be nice, if there was a way to make it show the positive and negative on non-polarised components.
Ian.M:
Pin order for two pin components in a SPICE netlist is significant. <shock><horror> Film at 11! <horror></shock>  :horse:

Its no different to choosing the 'wrong' direction for one of the current loops in a mesh analysis - it all comes out 'in the wash' with the only difference being the sign of the numerical result for that loop current, or in the case of SPICE, for that component current.  It only becomes important when that component current is used in other calculations not directly related to the nodes it is connected between. (e.g. behavioural sources), where the convention for formally laid out schematics is to insert a 0V voltage source as a current probe point which has indicated polarity. 

However, after you've run a LTspice analysis, when selecting nodes or currents to plot the cursor shows a red arrow indicating the direction of positive current when hovering over a two pin component, so redefining resistor symbols to add polarity symbols is unnecessary, and will cause problems if you want to share your schematics.

For further entertainment, look at the currents through the four identical capacitors in series in the attached sim!
iMo:
The icon shows always the same direction (thus indicating the node 1 and 2), current direction regardless..
exe:

--- Quote from: robint on February 20, 2023, 10:30:02 am ---FWIW its an indispensable tool and forces design thinking rather than the dirty suck-it-and-see approach by rank amateurs.

--- End quote ---

Ha-ha-ha, you don't know how I (ab)use LTSpice)
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