Conventional Current Flow vs. Electron Flow

[Montelores]

Could someone with electrical experience please explain how to reconcile the difference between the two?

For example, in a conventional flow diagram, the direction of current flow runs from positive source, then through the circuit to the negative terminal (in a DC circuit).

However, the actual electron flow is in the reverse direction.

So, for example, we see a diode in a circuit. A diode allows current flow in only one direction, and the schematic representation of a diode is an arrow (current flow) against a perpendicular line.

So does a diode actually function in the reverse direction from the depiction?

And, if an electrical circuit has its components placed in a specific sequence (assuming positive-to-negative current flow), how does that sequence still function when the electrons are actually flowing in the opposite direction?

Thanks -

Monty

 

[sceva]

From my Physics class days I remember that all the formulas assume positive to negative despite it being the opposite in reality. The bottom line was that it didn't matter.

I would be curious to find out more myself. What about DC vs AC? In AC with a diode does only every other pulse go thru, converting to DC?

 

[Ale-8(1)]

Can't add anything. I learned that it was the bass-ackwards arrangement and to just not worry about it. :wink: :lol: :wink:

 

[NikA]

I can answer the AC diode question: yes, the diode basically truncates the AC sine wave. There is a device consisting of multiple diodes, called bridge rectifier, that converts the AC sine wave to something like a constant DC signal.

I don't really understand the question about flow vs. current diagrams. The convention was made up before physics knowledge of the electron as the current carrier. The convention is at least self-consistent. The components generally function in the same sense regardless of which convention you follow, as long as they are treated in that convention.

 

[Montelores]

When we construct a circuit, we're predicating the sequence of components on the desired result.

But it turns out that the circuit actually functions backwards, from the manner in which we have assembled it.

So let's say that we need to install a resistor prior to a LED (the link will show the circuit schematic):


The circuit in the following figure shows a 6-volt battery supplying current to a light-emitting diode (LED) through a resistor (shown as a zigzag). LEDs (like many other electronic parts) eat up current like a kid eats candy: They try to gobble up as much as you give them. But LEDs run into a problem — they burn themselves out if they draw too much current. The resistor in the circuit serves the useful function of limiting the amount of current sent to the LED (the way a good parent restricts the intake of candy).

https://www.dummies.com/programming/electronics/components/what-are-resistors-used-for/


So how does the resistor in this case actually protect the LED, if the electrons are flowing first through the LED, and THEN through the resistor?

Monty

 

[P89DC]

It doesn't really matter for electronic circuits. Its only an agreeded upon sign (+ or -) for positive and negative currents. Its only important to stay with the agreed upon convention. Fun fact: back in the 1800s when they agreed upon the sign they had a 50/50 chance of having both agree but they got it wrong.

 

[NikA]

Ah, I understand better the question now.

The resistor is approximately equivalent to a flow restrictor in a liquid plumbing system. It can actually be placed on either side of the LED since it will reduce the current either way.

The reason metals are good conductors is that they are just chock full of free electrons, sort of like pipes in your plumbing supply are full of water right up to the tap. The electrons will eventually move all the way from the negative to positive, but all along the way they are displacing electrons that were available in the metal prior to conduction. So, like a flow restrictor, the resistor will slow down electron flow through the whole circuit, regardless of its location.

 

[Montelores]

Thanks to both for the responses -

My understanding, electricity first being discovered by Benjamin Franklin was not understood in the context of electrons, since atomic structure had not yet been discovered, so the "positive - negative" nomenclature didn't correspond to the actual physical movement of electrons (which carry a negative charge).

And, yes, good conductors carry spare electrons in the electron shell, which are actually displaced by the new electrons introduced from the power source (like Pez candy moving through a dispenser), so, while electricity doesn't actually move at the speed of light, it moves at the speed at which the electrons are displaced.

My example of the resistor and LED was just a choice for convenience, not for a specific circuit.

So an electrical circuit can have the components arranged in any sequence, as long as they are present to modify the current or voltage through the entire circuit, no matter their position?

How about a diode? Doesn't that operate in a defined linear direction?

Thanks for the help -

Monty

 

[NikA]

The rearrangement is often valid, but it breaks down in the case of logic elements like diodes and transistors. These devices operate as gates for electrons on the atomic level, so they'll only work in one sense of the circuit. Basically, the electrons cannot flow in one direction due to the material properties; they are closer to how you're envisioning electron flow.

It's been a while since I've really dug into circuit design on this level, so I'll just leave it at that.

Oh, and a light emitting diode will also only work when connected in one direction.

 

[Pat-inCO]

Since someone mentioned ol' Ben and his lightning:
It was not until the development of really high speed photography that we found out
the initial strike of lightning goes from ground to the cloud, and only then does the
real explosion happen. The up strike is in miliseconds and then the KA-BOOM
happens as the charge in the cloud is expended.

Taint 'lec-tri-city fun?

'nuther fun fact: The lightning rod is NOT to provide a path to ground for the charge
in the cloud, but rather to disperse the charge in the ground so it does NOT build
up high enough for the strike to occur. :wink:

 

[Jeepnik]

As an instructor once said, "Physical laws are man's way of explaining magic". So it's really all just magic no matter what you call it.

 

[JFB]

...The bottom line was that it didn't matter....

... and to just not worry about it. :wink: :lol: :wink:

can't provide any explaination, just sharing this tidbit

I was a Mechanical Engineer, Hired, at that time the world's biggest (and best) company that made electrical devices. to install, complex electronic systems, they "taught" mechanicalengineers how to relate electronic "drawings" to mechanic and hydrualics. the reason being we would NOT care about the electronics and if something didn't work, just replace it.

voltage is pressure and current is flow,
diodes are checkvalves, resistors are orifices, capaicators / inductors are accumulators

And in the words of Sir Lucas. All electronics work because of magic smoke...let that smoke out and they don;t work

 

[blume357]

have not thought about it for almost 40 years... but yes... DC current going towards the negative seems the right direction. Bought a new LED Bathroom Cabinet light a few years ago.... dern thing glows in the dark... I was kind of worried that the Chinese might have put some kind of radioactive substance in it to increase the output but a LED expert explained it to me that most of these use capacitors to supply a steady current to the LEDs and those will still bleed some current even when no power is running into the system.

 

[Poco Oso]

And in the words of Sir Lucas. All electronics work because of magic smoke...let that smoke out and they don;t work

A-h-h yes. Lucas, The Prince of Darkness. (I've owned both Triumph and Norton)

 

[Rick Courtright]

A-h-h yes. Lucas, The Prince of Darkness. (I've owned both Triumph and Norton)

Hi,

Did you ever have a Lucas refrigerator, Steve? I think they work on the smoke, too...

There were a number of British cars and a bike or two hanging around our neighborhood for a few years...

Rick C

 

[Bull Barrel]

Lucas refrigerators are why the Brits drank warm beer.

 

[Montelores]

A-h-h yes. Lucas, The Prince of Darkness. (I've owned both Triumph and Norton)

Hi,

Did you ever have a Lucas refrigerator, Steve? I think they work on the smoke, too...

There were a number of British cars and a bike or two hanging around our neighborhood for a few years...

Rick C

It looks like one needs a Whitworth spanner to top off the reservoir...

:wink:

Monty

 

[Poco Oso]

A-h-h yes. Lucas, The Prince of Darkness. (I've owned both Triumph and Norton)

Hi,

Did you ever have a Lucas refrigerator, Steve? I think they work on the smoke, too...

There were a number of British cars and a bike or two hanging around our neighborhood for a few years...

Rick C

No, no Lucas refrigerator, but there were a few nights, on a dark, winding, backroad, where I sure could have used some of that replacement smoke.

The Lucas formula for motorcycling:

A moonless night/ two lane road/long, sweeping curve/30°+ lean/45+mph= loss of headlight.

 

[jgt]

To this day, no one knows what electricity is. We know things about it, but we still don't know what it is. As for lightening. It strikes from both the earth or the cloud. If the cloud is negative and the spot on the ground is positive it will strike from the cloud. If the spot on the ground is negative and the cloud is positive it will strike from the ground up. When I was in collage I was taught the positive flow to negative was called the electron theory and the negative to positive flow was called the hole theory. However you want to think of it, it is way too involved to explain in a post here.

 

[gramps]

Sorry, but the flow of electricity is from positive to negative! Just as water in a hose under pressure. Always seeking ground. Like water electricity takes the shortest path to ground (negative pressure). It isn’t magical, it isn’t voodoo. It is well understood or we wouldn’t have computers.
gramps

 

[JFB]

an AC question tha stumped asked by a junior engineer.

therory is that the electrons that flow out during one half cycle return during the second half cycle.
In the electrical system grid there are hundred of generators all synched together.
do the electrons return to the same generator?

 

[gramps]

AC electricity is NOT PULSED! It is a wave that goes positive and negative, not back and forth.
gramps

 

[jgt]

Your're right gramps, so tell us why early 4020s had the positive grounded to the frame?

 

[Poco Oso]

My '54 Ford was 6v, positive ground.

 

[Poco Oso]

AC electricity is NOT PULSED! It is a wave that goes positive and negative, not back and forth.
gramps

AC vs DC current.

https://www.scienceabc.com/innovation/ac-vs-dc-alternating-current-or-direct-current-which-is-better.html

Snip:
The current (electric charge) only flows in one direction in case of DC (direct current). But in AC (Alternating current) electric charge changes direction periodically. Not only current but also the voltage reverses because of the change in the current flow

 

[gramps]

Your're right gramps, so tell us why early 4020s had the positive grounded to the frame?

.
Send me the schematic. I have no idea what a 4020 is. Maybe it is a feedback circuit of some kind like an oscillator or amplifier?
gramps

 

[Poco Oso]

John Deere 4020

https://wiringall.com/jd-4020-wiring-diagram.html

The 24v was a split 12v. (two 12v batteries) One positive ground, one negative.

Edit: to restore link

 

[jgt]

I guess we better not discuss hysteresis then huh?

 

[JFB]

John Deere 4020

https://www.tractor-specs.net/john-deere/jd-4020.html

The 24v was a split 12v. (two 12v batteries) One positive ground, one negative.

Interesting. . .

I would also like to see some schematics (the link wants to add software so no luck there)

A positive/negative center ground DC supply is very common for "Signal" electronics, but don't see the advantage for "Power" circuits.

Maybe the 4020 uses elctronic position control for its hydrulics?

 

[JFB]

I was able to veiw schematic on your first link.

that was my first look at a dual battery 24 VDC vehicle.

Looked like the way to go to provide 24 VDC for a Heavy duty starter AND to balance the generator loading using the two seperate 12 V lightings and instrument circuits (with frame return to reduce that wiring).

are big trucks wired the same?