beenthere,

It is apparently one of those things that present problems for some people. I always thought that once you learned that it was electrons that carried the charges, the question was forever settled. "Conventional" current is confusing, as it is incorrect.

Electrons don't always carry the charges. There are positive charge carriers also.

To speak of a "positive" versus a "negative" current seems absurd. It's simply current - electrons moving charge from a negative voltage point to a more positive voltage point, with the voltage difference providing the energy to force the movement.

It is positive with respect to the assumed direction. And current does have a direction. Any ammeter can prove that. Don't forget to add that into the definition.

Ratch

 

The only time I was ever concerned about the indication on my ammeter was when I was using a Simpson 260. The sharp little tick meant I had the leads backwards. The current never was altered by the meter leads. My Fluke DVM reads the same current no matter which way the leads are connected. Any "positive" or "negative" indication is simply a convention.

I put an ammeter in my 1965 Ford. It indicated right of 0 when charging, and left of 0 when discharging (center 0, obviously). Surely you would not maintain that I had both positive and negative current in the same set of wires? The ammeter faithfully showed positive and negative readings, though. I don't think that an ammeter makes the rules.

 

beenthere,

The only time I was ever concerned about the indication on my ammeter was when I was using a Simpson 260. The sharp little tick meant I had the leads backwards. The current never was altered by the meter leads. My Fluke DVM reads the same current no matter which way the leads are connected. Any "positive" or "negative" indication is simply a convention.

I looked up the operators manual for the 260. It says to connect the positive red lead to the + supply voltage for current measurement. That tells me that it is a conventional current responding unit. It also conveniently reverses the leads by the switch.

Some sophisticated meters have a rectifying bridge that will channel the current for a positive deflection no matter which way the leads are connected. There is probably a way it indicates the current direction.

I put an ammeter in my 1965 Ford. It indicated right of 0 when charging, and left of 0 when discharging (center 0, obviously). Surely you would not maintain that I had both positive and negative current in the same set of wires?

You had a center zero meter that indicated different current directions, but not at the same time.

The ammeter faithfully showed positive and negative readings, though. I don't think that an ammeter makes the rules.

That proves that current has a direction. An ammeter is manufactured according to a set of rules, and can then be used to determine current direction.

Ratch

 

thatoneguy,

In short, although you are hopelessly pedantic, I agree with you on this.

Thank you. I appreciate that. I believe many others also agree, but they just won't for whatever reason say so.

Ratch

 

When you say -

An ammeter is manufactured according to a set of rules

- , you miss a crucial point. The ammeter with a D'Arsonval movement can only deflect in one direction. Thus, you let the machine make the rules.

And by -

center zero meter that indicated different current directions, but not at the same time

- do you mean there is a quantum ammeter that indicates all possible currents simultaneously? I thought they all worked with one current at a time.

By the way, it is any AC ammeter that always shows deflection in the same direction. Something about indicating an absolute value.

But I do agree that current has a direction - negative to positive. We're always shuffling electrons around.

 

beenthere,

- , you miss a crucial point. The ammeter with a D'Arsonval movement can only deflect in one direction. Thus, you let the machine make the rules

One direction only, yes. But you can determine what you will call the positive lead of the meter. So it is the manufacturer that makes the rules.

- do you mean there is a quantum ammeter that indicates all possible currents simultaneously? I thought they all worked with one current at a time.

They do. When you said "Surely you would not maintain that I had both positive and negative current in the same set of wires?", I thought you were saying both currents were running concurrently. To better answer your statement; yes, you have both positive and negative current direction referenced by the meter existing in the wires at various times.

By the way, it is any AC ammeter that always shows deflection in the same direction. Something about indicating an absolute value.

What are we talking about now? A D'Arsonval movement with external circuitry to measure AC, or a moving-vane meter movement that can measure AC directly?

Ratch

 

But you can determine what you will call the positive lead of the meter.

I'm going to call it Solanum tuberosum.

If you don't have a problem with it, why keep harping on it?

 

This is a bit like making a meter stick with the graduations running from right to left. When you apply it to measure some interval with the stick in a usual orientation, you claim to be measuring a negative distance.

 

thingmaker3,

I'm going to call it Solanum tuberosum.

If you don't have a problem with it, why keep harping on it?

Have you asked any others in this thread, including yourself, the same question? I was responding to a statement, and defending my assertions.

Ratch

 

Have you asked any others in this thread, including yourself, the same question?

Count the posts, my pedantic friend. You are the Hole Avenger!

Others in the thread are free to comment on questions as they wish. This is an equal opportunity forum. I suspect they all know this.

As for myself, I have declared since your arrival in May of last year that I accept both models.

I also note you evaded the question. I reiterate: If you don't have a problem with it, why keep harping on it? Simply for the joy of debate, perhaps?

 

thingmaker3,

I also note you evaded the question. I reiterate: If you don't have a problem with it, why keep harping on it? Simply for the joy of debate, perhaps?

I beg to differ with you about evading the question. I said "I was responding to a statement, and defending my assertions." That sounds like a response to your question.

But I don't think the number of posts I make, or whether you believe in a model, or whether I vigorously defend a model is a good criteria for singling only me out for critiism. Now if my posts were not cogent, off topic, or fallacious, then you would have a good reason. For the most part, I was answering statements other have made.

Ratch

 

Electron flow is the norm nowdays. Unfortunately conventional flow theory lasted long enough to help dictate how components were drawn. They would have been slightly more intuitive otherwise.

It's all Ben Franklin's fault. There was a great article in Popular Electronics....probably 30 years ago, now...."Was Ben Frankliin Crazy?"

Franklin had perfectly described ion motion with his electrolytic solutions (he did electroplating). Of course, they weren't called ions then. But he did understand that SOMETHING ws moving from the positive anode to the cathode.

At the time ion flow made much more sense...ions had the bulk of the mass...and electrons hadn't been discovered yet.

Anyway...it's always better if you can blame a dead guy in matters like this.

Eric

 

It is fairly important that to understand the physics that all the equations of current are written using conventional current. And current is not really a scalar value it really should be considered a vector. Sign is just a simple way to manage this when only one dimention really matters. This argument has been fun for a while, but if you need the idea of electron flow and cannot understand the role of conventional current and that electrons are not the only charge carriers you should be fine, but stay away from chem. and physics, where you will be in serious trouble. If you understand both, use either, but when not following the well established convention, you should state it clearly.

Time to move on?

 

KL7AJ,

It's all Ben Franklin's fault. There was a great article in Popular Electronics....probably 30 years ago, now...."Was Ben Frankliin Crazy?"

No, that is a falsehood. If Franklin called electrons positive, then his electrochemical model would be backwards. The bottom line is that you cannot define current direction by the movement of charge carriers, because two different charge carriers exist. One of the models will be wrong for one carrier and correct for the other. The engineers and academics got it right by creating a convention that allows them to calculate the result from an assumed direction and polarity. If necessary, they can look back at the real charge carriers when finished to determine the real current direction.

Ratch

 

It is fairly important that to understand the physics that all the equations of current are written using conventional current. And current is not really a scalar value it really should be considered a vector. Sign is just a simple way to manage this when only one dimention really matters. This argument has been fun for a while, but if you need the idea of electron flow and cannot understand the role of conventional current and that electrons are not the only charge carriers you should be fine, but stay away from chem. and physics, where you will be in serious trouble. If you understand both, use either, but when not following the well established convention, you should state it clearly.

Time to move on?

The post above is the most succinct answer to all arguments.

My only "concern" is with the number of threads about it, and think of what people brand new to electronics might feel if they see all these definitions in addition to the huge learning curve. I've noticed more and more DIY beginners are STARTING with Microcontrollers. I guess typing is easier or something. Learning the analog concepts after doing things in code would not make sense to a large portion of people.

Look at what people are doing at Make magazine and instructables.com, the theory is glossed over, but people DO make nifty gadgets, and that is what they want to know more, they end up here. I don't think that is the best way to go at learning, as I've seen dumb and dangerous things on sites from links people have sent me.

Electronics isn't a religion, but you would Not know that by reading forums. With all the absolute arguments around, such as Tubes vs. Transistors, Electrolytic or Tantalum, wirewound or carbon film, and even which way current flows. Pick a convention, and stick with that convention. If you plan on being versed in multiple fields, plan on accepting both conventions of current flow.

Explaining how an inductor works to a newbie is hard enough, adding in which way the current is flowing doesn't simplify it. On that note, I never heard the term "Left Hand Rule" until this decade, that seems to be deliberate disinformation, as 'right hand rule' gives you the same information, but with a negative sign.

*sigh*

 

I thought i would break the tension with a limerick about my solution for dealing with those annoying "NO LEFT TURN" road-signs that are common in the USA.


My anger once grew to new heights,
When forced to turn left by three rights,
'Twas a matter of Law,
'Till the day that I saw,
All lefts are just negative rights.


It turns out that physics is not required training for my local police force, and based on the Judge's verdict, I must conclude that it is not covered too well in law school either.

 

yippeee......
we have completed more than half century posts....!!!!!!!
I hope we can make it a hundred pretty soon...

 

I only recently looked at this thread.

First
thanks for bringing out the conventions used in the E-book. I hadn't realised that as I don't look at it too often.

Second
What about alternating current? Which direction do the carriers move and which direction does any current move?

Third
What about node analysis methods, like Kirchoffs Current Law? We have to assume a convention here, either that currents into the node will be positive or that they wil be negative. One is bound to conflict with carrier flow. And since all real nodes have both ins and outs there must be some wrongly labelled.

Fourth
What about more complicated circuits. We simply don't know the current directions at the outset of an analysis. So it is important that we apply a consistent convention.

So overall I see no advantage in adopting yet another sign convention, unlike the change from imperial to metric or the change from CGS to MKS.

 

studiot,

What about alternating current? Which direction do the carriers move and which direction does any current move?

They move back and forth, as in alternating. Give me the voltage and the charge and I will tell you.

What about node analysis methods, like Kirchoffs Current Law? We have to assume a convention here, either that currents into the node will be positive or that they wil be negative. One is bound to conflict with carrier flow. And since all real nodes have both ins and outs there must be some wrongly labelled.

For all calculations, I always use the conventional current model. That means assuming all nodes have a positive voltage unless they have a negative voltage source directly connected to them. That means charge flows away from the node if the branch is connected to a less positive node. If the voltage is calculated to be negative, then the positive voltage assumption was wrong. I don't worry about the real carrier flow until I finish the calculations, and only if necessary.

What about more complicated circuits. We simply don't know the current directions at the outset of an analysis. So it is important that we apply a consistent convention.

If I don't know the current direction for sure, then I assume a direction and let the math prove me right or wrong. If the current calculation is a negative number, then my assumed direction was incorrect.

So overall I see no advantage in adopting yet another sign convention, unlike the change from imperial to metric or the change from CGS to MKS.

Have you read all the threads pertaining to the subject? As thingmaker3 said, I explained and defended the conventional current method ad nauseam.

Ratch

 

I meant to add that in this thread 'I find myself in complete agreement with Ratch.'

Well almost, because KCL has nothing to do with voltage. Currents, whether we choose electron or conventional direction, are +ve inward at a node and negative outward, or vice versa.

A more complicated example would be mesh current analysis, where we deliberately choose a set of ficticious 'mesh' currents, circulating in each loop of the mesh. Here we have a choice of clockwise +ve / anticlockwise -ve or vice versa convention, regardless of choice of electron or conventional flow.