Electronics > Beginners

Mesh Current Method, Sign Convention

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rstofer:

--- Quote from: sibeen on December 11, 2019, 12:01:22 am ---The interesting tidbit is that military techs, at least in the English speaking portion of the world, get taught electron flow. I've never been able to track down the why of that and it's always interested me as to why that occurred.

--- End quote ---

I think the military is still thinking about vacuum tubes and perhaps electron flow is easier when dealing with tubes.
Once institutionalized, it will never change.

I like current flow because I can follow the arrows on transistors and diodes.  Somehow, that is comforting.

rstofer:

--- Quote from: RoGeorge on December 11, 2019, 01:24:19 am ---Now I see what you mean, you were talking about the voltage arrow, right?

I didn't know there are two conventions, American and European   ::)

--- End quote ---

Now you see why I'm confused.  The RIGHT answer will be whatever the Prof says it is.  I just need to be more flexible in my thinking.

I believe we had an example of the American vs European approach in one of Simon's homework problems a long time back (2 years?).  As an aside, I don't recall ever drawing a voltage arrow when doing mesh equations.  I just labeled the assumed + and - ends of components and wrote the loop equation based on my assumed circuit path.

I'm going to drag out my textbook and make sure I'm not mis-remembering but it sure seems right that a battery is a voltage gain and a resistor is a voltage loss.  But I graduated in '73 so what do I know?

RoGeorge:
Indeed, whatever the teacher say.

Just to be clear, I know it like in the attached fig. 17.1 (a), (b) or (c), AKA CEI/IEC 60375 standard.  Khan Academy link was using the other convention, like in fig 17.1 (d).

rstofer:
17.1(b) works for me!

I went back to my text and they take a shortcut with the earliest problems:  They set the battery as positive on the left hand side of the '=' and then sum all the drops through resistors as positive on the right hand side.  That's fine, because if the drops were pulled to the left hand side they would all be negative and that's what I recall.

In the end, it doesn't matter and the Prof is always right so I'll just have to wait and see what they teach.

gcewing:
Most circuits will contain more resistors than batteries, so some people may find it easier to think in terms of voltage drops rather than voltage gains. That way most of the voltages will be positive rather than negative.

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