Well maybe i dont understand you correctly. How do *you* define the passive sign convention?And hopefully he will be able to work it out when he comes across a circuit analysis that doesn't blindly obey your dogmatic interpretation. Neither he nor we have any way of knowing that at this point. So how about we both give it a rest?
I'm not dogmatic about it and can work with either common interpretation. But when left up to me I prefer the interpretation that positive power is positive in a load that is absorbing power and positive in a source that is supplying power. This is for two reasons -- first, I prefer to (when practical) work with reference assignments such that if any quantity end up being negative that it can serve as a flag letting me know that I need to look at things more closely because either I didn't properly estimate the circuit behavior or I made a mistake somewhere in the analysis. Second, consider the following circuit:Well maybe i dont understand you correctly. How do *you* define the passive sign convention?
Now, I disagree with his claim that the electrical engineering uniformly adopts this interpretation of the passive sign convention -- though it isn't surprising that adherents to this interpretation can be as strident in claiming that it is the only interpretation, just like DGElder is in his claim -- but just as the case of the example above, consider how YOU generally assign reference polarities when you analyze circuits. I'd wager that you more commonly work in a manner consistent with this interpretation than with the one in which power delivered by sources is negative.To avoid confusion with regard to the sign of power, the electrical engineering community uniformly adopts the passing sign convention, which simple states that the power dissipated by a load is a positive quantity (or, conversely, that the power generated by a source is a positive quantity). Another way of phrasing the same concept is that if current flows from a higher to a lower voltage (+ to -), the power dissipated will be a positive quantity.
Hello again,I'm not dogmatic about it and can work with either common interpretation. But when left up to me I prefer the interpretation that positive power is positive in a load that is absorbing power and positive in a source that is supplying power. This is for two reasons -- first, I prefer to (when practical) work with reference assignments such that if any quantity end up being negative that it can serve as a flag letting me know that I need to look at things more closely because either I didn't properly estimate the circuit behavior or I made a mistake somewhere in the analysis. Second, consider the following circuit:
View attachment 106192
In order to adhere to the passive sign convention as interpreted by you and DGElder, you have to provide TWO currents for this circuit.
View attachment 106193
If you want to use a single current, then you have no choice but to assign one of the voltages such that it will turn out to be negative.
View attachment 106194
or
View attachment 106195
Do you want to work with any of these assignments? Wouldn't you agree that any of them increases the likelihood of making a mistake and also the potential for not catching it.
Doesn't the following seem much more reasonable:
View attachment 106196
Isn't this how you would set things up? But does this conform to your interpretation of the passive sign convention?
Note that it DOES conform to my preferred interpretation.
And it is NOT just MY interpretation. As an example:
From "Principles and Applications of Electrical Engineering" by Giorgio Rizzoni:
Now, I disagree with his claim that the electrical engineering uniformly adopts this interpretation of the passive sign convention -- though it isn't surprising that adherents to this interpretation can be as strident in claiming that it is the only interpretation, just like DGElder is in his claim -- but just as the case of the example above, consider how YOU generally assign reference polarities when you analyze circuits. I'd wager that you more commonly work in a manner consistent with this interpretation than with the one in which power delivered by sources is negative.
I wouldn't want to use any of the others -- and apparently neither would you. That's my point.Hello again,
I still dont understand one thing you are referencing: the assignments of voltage polarities in the diagrams. I am not sure why you would want to assign anything other than the last one, where both the source has upper positive lower negative, and the load has upper positive and lower negative.
Not as you and others are insisting it be used. You maintain that PSC has the reference direction for current for any element, source or load, be INTO the positive terminal (per the reference voltage for that item). That way you multiply the current by the voltage and if it comes out positive you are absorbing power and if it comes out negative you are supplying power. Well, in that last circuit both the current and the voltage will be positive. The only way to then end up with a negative power for the source is to apply a magical mystery minus sign!That arrangement satisfies the passive sign convention just perfectly, doesnt it?
The whole point of things such as the passive sign convention and others is specifically so you don't have to do a bunch of "deeming" things to be this or that and apply magical mystery minus signs to things as a consequence of the "deeming" process. The purpose is to define reference directions for the symbolic quantities such that, no matter how complicated the circuit gets, the math takes care of itself.In the load, the current ENTERS the positive terminal of the load so the load absorbs power and is deemed positive power. In the source, the current LEAVES the most positive terminal so it is supplying power and is deemed negative in the strictest sense of the convention, so i dont see why you would want to reverse any voltage polarity.
But note that all you have done is used the two currents as in the first diagram, you just have not written them down. This is fine, except now as you describe things to people you will likely find yourself either talking about currents that are not defined (such as saying that the source has a current of -10 A when the only current defined on the diagram has a value of +10 A) are applying magical mystery minus signs in order to take a voltage of +20 V and a current of +10 A and get a power of -200 W.Note that we dont really need two currents. If we say that a current flowing from left to right is positive then if we reverse the current arrow we say it is negative. We dont actually create a new current in doing this we just flip the sign, and then the positive source times the negative current equals a negative quantity.
I'll throw something together, probably later this week. I'm up against the clock right now on getting some stuff finalized and submitted.In a simple circuit where there is only one source there is little to confuse anyone about if it is supplying power or not, especially in a passive circuit. When things become more complicated though as with multiple sources, it's good to have a signed power so that sources that are absorbing power can be quickly distinguished from sources that are supplying power. That's why i was looking at the questions about the three source circuit i mentioned. If you care to draw up a circuit like that where maybe one source is dissipating power and two are supplying power, then we might see how handy this idea becomes. We dont have to write "supplying power" and "dissipating power" for example, we just write the sign of each power.
Who said that you throw away all directional information? Here you are claiming that all three sources are either delivering power or that they are all absorbing power (depending on which interpretation you are using).Hi again,
Ok then here is the list without any signs and any extra notes:
V1: 5 watts
V2: 10 watts
V3: 10 watts
R1: 2.5 watts
R2: 2.5 watts
I don't like having conversations by PM unless it is something that is confidential. Other people can read and learn (or ignore) as suits them.Hello again,
It appears that we are just not understanding each other because there are too many discrepancies cropping up that would not be there if we actually did understand each other. For example, i never said that the three sources were either ALL delivering or ALL absorbing, i said that either of them could be either delivering or absorbing, but they dont have to all do the same thing, and you said you dont like to use negatives yet you used a negative in your last example. All this leads me to believe we wont be able to progress in this discussion without 10 more replies back and forth
Perhaps in a PM would be more appropriate, if you're still interested that is
Where you just simply got rid of all the signs and all the notes. That means that you are saying that V1, V2, and V3, all have powers that are positive. If you are using any kind of consistent sign convention, then positive power on a source either means that it is delivering power or that it is absorbing power. But regardless of which you choose, the three sources above all have the same sign and so they are either all delivering power or all or all absorbing power. You have to do something to distinguish the two possibilities and that is either use a sign or use a notation.Hi again,
Ok then here is the list without any signs and any extra notes:
V1: 5 watts
V2: 10 watts
V3: 10 watts
R1: 2.5 watts
R2: 2.5 watts
by Aaron Carman
by Aaron Carman
by Duane Benson
by Jake Hertz