connecting to 0 volts.

[krayvonk]

cant u just connect to any piece of metal, and its as good as a 0 volts connection?

[AVGresponding]

No, as there would be no useful current path.

A 0 volts connection needs to be part of the circuit; without a meaningful current flow the metal you connect just becomes "live" at the potential of the point you connected it to.

[rsjsouza]

What are you connecting? There is not much information available about the circuit/environment to take an educated guess.

0V is a reference to another potential. If you have a car battery, for example, the "0V" is, by the most common convention, wherever you connect the black/negative terminal. If you are talking about your house's outlet, the convention is that the Ground pin is the 0V (in some installations, the neutral can be connected to the ground at a specific point of the line).

[krayvonk]

Heres an instructable to make a ground...  but...  it just looks like a piece of metal you connect to,  I dont understand.

https://www.instructables.com/id/Build-a-Quick-Easy-Free-Ground-Terminal/

By touching the metal to the circuit isnt it a meaningful connection already -  because its an endpoint,  just like + and -.

[IanB]

I think you missed the point of the instructable.

The idea is to create a common "star ground terminal" where you connect all the ground leads of various devices in a test or experimental setup to keep them all referenced to a common potential and avoid ground loops.

The reason why it is "just a piece of metal you connect to" is that everything is connected to it, and if it was not metal it would not conduct electricity.

[wraper]

That instruction is a piece of junk as well as it's result. Making a turn of wire around paperclip does not result in reliable connection. Also I don't get what it the purpose of anything besides paperclip. As those bits do absolutely nothing.
 

[wraper]

If you need common connection for a bunch of wires, simply buy WAGO terminal block or similar.

[krayvonk]

I think you missed the point of the instructable.

The idea is to create a common "star ground terminal" where you connect all the ground leads of various devices in a test or experimental setup to keep them all referenced to a common potential and avoid ground loops.

The reason why it is "just a piece of metal you connect to" is that everything is connected to it, and if it was not metal it would not conduct electricity.

A ground isnt just another conduction path from positive to negative,  its supposed to suck from positive and blow to negative, 0 volts potential.     Seems wierd,  I connect half my battery through an led to the sink, and nothing happens,  but i swear it was doing it before with a dc motor.   Its like god is deactivating electricity on me, so I never get off the ground. 


Whats inside that Wago block?  how does it work?

[wraper]

Seems wierd,  I connect half my battery through an led to the sink, and nothing happens

It would be weird if something happened. As already said by IanB, it's simply a common reference point in the circuit where you connect everything and call it a "ground" http://www.tpub.com/neets/book1/chapter3/1-18.htm . It does literally nothing by itself. It does not suck or blow anything. And you need closed path for current to flow. You cannot simply connect one terminal of a battery to something and the expect something to happen. https://www.dummies.com/programming/electronics/components/closed-open-and-short-circuits/

Whats inside that Wago block?  how does it work?

Piece of metal. It's simply a connector with multiple terminals connected together.

[IanB]

A ground isnt just another conduction path from positive to negative,  its supposed to suck from positive and blow to negative, 0 volts potential.

It's supposed to what, now? 

Here is where I give a very strange bit of advice. When you are learning about science, forget everything you think you have read, or heard people say. Put your textbooks to one side.

The only way to find the truth is to do your own experiments. Follow in the footsteps of every scientist through history. Nothing is ever true because it is "supposed" to be that way. It is true because if you do the experiment you can verify it.

So here is your goal: find out by experiment if you can make some object that sucks electricity out of a positive battery terminal, or pushes electricity into a negative battery terminal, without some kind of closed circuit with a return path for the current. Come back and let us know what you find.

[james_s]

Voltage at a node is always stated relative to some other node. It's convenient to pick one particular node and call it "ground" and reference everything back to that point but in reality it's arbitrary. You could pick any node in the circuit you want and measure all your voltages relative to that, it will make no difference at all except that your measurements won't make any sense to someone else if they don't follow the convention.

[wraper]

Here is where I give a very strange bit of advice. When you are learning about science, forget everything you think you have read, or heard people say. Put your textbooks to one side.

The only way to find the truth is to do your own experiments.

Quite crappy advice IMHO because you don't know what you don't know. So experimenting without a clue of what you are doing is not only ineffective in sense of things learned vs time spent but likely will result in wrong conclusions.

Nothing is ever true because it is "supposed" to be that way. It is true because if you do the experiment you can verify it.

And that explains never ending supply of perpetuum mobile.

Follow in the footsteps of every scientist through history.

Yeah, do so. You only need a few hundreds of years for doing it the same way.

[Prehistoricman]

Quite crappy advice IMHO because you don't know what you don't know. So experimenting without a clue of what you are doing is not only ineffective in sense of things learned vs time spent but likely will result in wrong conclusions.

This brings me back to early school life where the teachers gave the class a couple of lightbulbs, many wires, and some batteries, and let us do whatever we liked. Most of the kids were just making crazy loops out of the wires and not paying any attention to current flow at all.

[krayvonk]

Ok.  thanks for the help.

Ill have a hard think, but basicly I was thinking I had a component that doesnt actually exist,  maybe I need to think about like that more, if I want to understand it better.   
Maybe having a look at voltage dividers might give me the solution.

[krayvonk]

Ok,  ive got you all now.  what if I have a multi voltage point circuit composed of 2 batteries?

So if I have a 9v battery and a 4.5v battery connected to a circuit.

then i have 9v +   9v-  4.5v+  4.5v-

the 4.5v battery would be the "ground"  in this case, but with a higher medium and lower medium.  this is what i want, because i have an idea for an analogue subtraction circuit and it needs this "impossible ground" to work.

4.5v positive would count as negative to 9v positive, would it not?

[Siwastaja]

Note that voltage, by definition, always is between two points.

You select any two points, and the voltage can be measured between them.

There is no such a thing as a voltage at a single point. Yet, we engineers talk like that all the time. What's going on?

For convenience, when we talk about "voltage at point x" (a single point), we actually mean voltage between points x and y, where y is any assumed point we think we agree on!

Sometimes, this can be called "GND", for example, but it can be called something else, and it can be basically any arbitrary point in circuit.

In some circuits, the choice of "GND" is kind of obvious, but it always isn't. And it never is a physical entity, it's just a naming choice by the designer.

A single block of (very conductive) metal has voltage of approx. 0V between any two points of that metal block. If you measure the voltage between this metal block, and say, another metal block, the voltage between them depends on what kind of circuitry is connected between them.

[krayvonk]

Yes.  it would involve having a conductive metal,  its not allowed to be dielectric or our batteries would be draining into thin air.
But this does not explain why my "ground experiments" are failing dismally.       no flow.  I think im going to start going to church.

[Siwastaja]

But this does not explain why my "ground experiments" are failing dismally.       no flow.  I think im going to start going to church.

Draw your circuit and show us. You know, using battery symbols or even MS Painting with battery pictures and lines as wires. It's so much easier to understand from a picture, than from words.

[Brumby]

I've used this graphic somewhere else on this site ... but it might be useful:



All 3 represent the exact same battery connections - it's just where you place the meter probes that changes the numbers.

[krayvonk]

definitely useful for confusing ppl.

[wraper]

definitely useful for confusing ppl.

There is nothing confusing. It's just some crap idea which is stuck in your head is preventing you thinking rationally.

[Siwastaja]

Yes, you clearly have some excess, complicated idea in your head. This is unsurprising, given how people talk about "grounds" and all that shit.

Try to get rid of all these ideas.

[krayvonk]

ok, let me add more to the confusion myself. 

[Zero999]

ok, let me add more to the confusion myself. 

The top resistor has 7V across it and the bottom resistor 17V across it. No current flows in or out of the 5V rail, which simply biases the entire circuit Change the 5V rail to 0V, an V(A) = +7V & V(B) = -17V or change it to 100V and V(A) = 107V and V(B) = 83V. The currents and voltages across each resistor remain the same, but they get shifted up or down..

I was talking nonsense there! Current does flow through the 5V rail and changing the voltage on the 5V rail would affect the currents in the rest of the circuit. I had a huge brainfart. 

[Brumby]

Presuming the voltages you have shown are what a meter would show when you put the red probe on each of those points, let me ask you to do ONE thing.....  Show where you would put the black probe from your multimeter when you do those measurements (ie - the reference point).

The reason for asking this is that those voltages are rather meaningless without knowing where the reference point is.