Author Topic: connecting to 0 volts.  (Read 1239 times)

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Offline krayvonk

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connecting to 0 volts.
« on: March 15, 2020, 05:01:25 pm »
cant u just connect to any piece of metal, and its as good as a 0 volts connection?
 

Online AVGresponding

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Re: connecting to 0 volts.
« Reply #1 on: March 15, 2020, 05:39:44 pm »
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.
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Offline rsjsouza

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Re: connecting to 0 volts.
« Reply #2 on: March 15, 2020, 05:56:04 pm »
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).
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Offline krayvonk

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Re: connecting to 0 volts.
« Reply #3 on: March 15, 2020, 06:22:33 pm »
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 -.
« Last Edit: March 15, 2020, 06:24:33 pm by krayvonk »
 

Offline IanB

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Re: connecting to 0 volts.
« Reply #4 on: March 15, 2020, 06:51:08 pm »
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.
I'm not an EE--what am I doing here?
 
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Online wraper

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Re: connecting to 0 volts.
« Reply #5 on: March 15, 2020, 07:05:54 pm »
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.
 :palm:
 

Online wraper

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Re: connecting to 0 volts.
« Reply #6 on: March 15, 2020, 07:08:37 pm »
If you need common connection for a bunch of wires, simply buy WAGO terminal block or similar.

 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #7 on: March 15, 2020, 07:36:08 pm »
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.  :P


Whats inside that Wago block?  how does it work?
 

Online wraper

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Re: connecting to 0 volts.
« Reply #8 on: March 15, 2020, 07:47:27 pm »

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/
Quote
Whats inside that Wago block?  how does it work?
Piece of metal. It's simply a connector with multiple terminals connected together.
« Last Edit: March 15, 2020, 07:49:20 pm by wraper »
 

Offline IanB

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Re: connecting to 0 volts.
« Reply #9 on: March 16, 2020, 12:37:29 am »
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?  :o

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.
I'm not an EE--what am I doing here?
 

Offline james_s

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Re: connecting to 0 volts.
« Reply #10 on: March 16, 2020, 12:46:38 am »
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.
 

Online wraper

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Re: connecting to 0 volts.
« Reply #11 on: March 16, 2020, 12:52:56 am »
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.
Quote
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.
Quote
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.
« Last Edit: March 16, 2020, 01:00:12 am by wraper »
 

Offline Prehistoricman

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Re: connecting to 0 volts.
« Reply #12 on: March 16, 2020, 12:58:23 am »
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.

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #13 on: March 16, 2020, 06:29:27 am »
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.
 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #14 on: March 16, 2020, 08:46:51 am »
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?
« Last Edit: March 16, 2020, 08:50:26 am by krayvonk »
 

Online Siwastaja

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Re: connecting to 0 volts.
« Reply #15 on: March 16, 2020, 09:17:20 am »
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.
 
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Offline krayvonk

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Re: connecting to 0 volts.
« Reply #16 on: March 16, 2020, 09:27:39 am »
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.
« Last Edit: March 16, 2020, 09:30:12 am by krayvonk »
 

Online Siwastaja

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Re: connecting to 0 volts.
« Reply #17 on: March 16, 2020, 09:46:05 am »
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.
 

Online Brumby

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Re: connecting to 0 volts.
« Reply #18 on: March 16, 2020, 09:48:56 am »
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.
« Last Edit: March 16, 2020, 09:52:22 am by Brumby »
 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #19 on: March 16, 2020, 11:37:14 am »
definitely useful for confusing ppl. :)
 

Online wraper

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Re: connecting to 0 volts.
« Reply #20 on: March 16, 2020, 11:41:37 am »
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.
 
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Online Siwastaja

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Re: connecting to 0 volts.
« Reply #21 on: March 16, 2020, 11:47:09 am »
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.

 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #22 on: March 16, 2020, 11:53:09 am »
ok, let me add more to the confusion myself.  8)

 

Online Zero999

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Re: connecting to 0 volts.
« Reply #23 on: March 16, 2020, 12:00:24 pm »
ok, let me add more to the confusion myself.  8)
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.  :palm:
« Last Edit: March 16, 2020, 12:17:12 pm by Zero999 »
 

Online Brumby

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Re: connecting to 0 volts.
« Reply #24 on: March 16, 2020, 12:10:41 pm »


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.
 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #25 on: March 16, 2020, 12:11:10 pm »
I do lose half the current down the left side,  because its 2 resistors versus one.  (which i wish wouldnt happen, but its true, and using potentiometres introduces error to it.)
If it were an exact ground. id have no current, because a-a=0.

But if the resistors were different you would get current there.   But as it sits in error at 5v,  that means it would be flowing towards the left, in my mind, because the potential difference is GREATER.


[EDIT]
Brumby,  they are not multimetre measurements, they are NOT current limited,  they are just raw voltages from batteries. at those positions.
« Last Edit: March 16, 2020, 12:13:20 pm by krayvonk »
 

Online Brumby

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Re: connecting to 0 volts.
« Reply #26 on: March 16, 2020, 12:13:38 pm »
Do us a favour .... show us the whole circuit - with all the components (including power sources) and all the connections.
 

Online Brumby

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Re: connecting to 0 volts.
« Reply #27 on: March 16, 2020, 12:17:56 pm »
Just for good measure - if all your power sources are batteries, you can stop using the word "ground".  It is irrelevant.  Completely, totally and wholeheartedly irrelevant.
 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #28 on: March 16, 2020, 12:18:35 pm »
It is the whole circuit, do you need me to show you the application as well? :)

just think of the resistors as potentiometres,  and the battery connections are solid and unchanging.

There is error in the result, because of load theft on the potentiometres,  when you increase the power of "operand b" itll actually draw more current down the side from "operand a", so it would give you a more contrastive result than a correct subtraction.

I wished the bare "ground pole" (which is the low PotentialDifference battery...) would short away because its 100% loadless,  but I forgot both operands have a resistor/potentiometre so that wouldnt happen.   So it doesnt work that well anyway.
« Last Edit: March 16, 2020, 12:22:16 pm by krayvonk »
 

Online Zero999

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Re: connecting to 0 volts.
« Reply #29 on: March 16, 2020, 12:23:24 pm »
It is the whole circuit.

just think of the resistors as potentiometres,  and the battery connections are solid and unchanging.

There is error in the result, because of load theft on the potentiometres,  when you increase the power of "operand b" itll actually draw more current down the side from "operand a", so it would give you a more contrastive result than a correct subtraction.

I wished the bare "ground pole" (which is the low PotentialDifference battery...) would short away because its 100% loadless,  but I forgot both operands have a resistor/potentiometre so that wouldnt happen.   So it doesnt work that well anyway.
The two resistors form a potential divider. The output resistance is equivalent to both their values in parallel, half of 1k, as they're both the same and the output voltage is 0V, half way between -12V and +12V. The equivalent circuit is simply 500 Ohms, connected to 0V, so the current taken by the 5V supply is 5/500 = 10mA. This is all assuming the other sides of the 12V power supplies are connected to 0V.

I agree, not drawing circuits clearly and doing things such as omitting the ground connection, can cause confusion.
 
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Offline krayvonk

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Re: connecting to 0 volts.
« Reply #30 on: March 16, 2020, 12:26:14 pm »
connected to 0v?   +12v connects to -12v.

hehe.  24V!! double your POWA!!!
 

Online Zero999

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Re: connecting to 0 volts.
« Reply #31 on: March 16, 2020, 12:32:46 pm »
connected to 0v?   +12v connects to -12v.

hehe.  24V!! double your POWA!!!
Yes, assuming the other sides of the 12V supplies are connected to 0V, the Norton's equivalent circuit for that potentiometer is just a 500 Ohm resistor connected to 0V. It does have 24V across it, because that's the potential difference between +12V and -12V.

All voltages are relative. What confused me when I initially replied, was I made the assumption that the other side of the 12V supplies are connected to +5V, rather than 0V.

And you haven't shown the complete circuit, because there's no 0V connection. If you entered that circuit into SPICE, it would refuse to simulate it.
 

Online Siwastaja

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Re: connecting to 0 volts.
« Reply #32 on: March 16, 2020, 12:35:52 pm »


I can see why this might be confusing to total beginners, though.

There are two different concepts mixed, without clear indication which is which.

There are numbers that directly represent voltage differences: the "9V" labels next to the batteries. They describe a voltage between two points in circuits (namely, the battery terminals). This is the only physical definition of voltage. A telltale sign in this picture is that the labels indeed are not next to any single point, they are in the middle of two points.

Then there are the numbers that represent a "potential" at a single point. These refer to each other; if one node says "+9V" and another says "-9V", the voltage between these two points is 18V (or -18V, depending on which way you measure). But you could call them +1009V and +991V, as well, and the result is the same. Voltages are differences, and the reference of such "single point potentials" is an arbitrary choice.
 
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Offline krayvonk

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Re: connecting to 0 volts.
« Reply #33 on: March 16, 2020, 12:37:31 pm »
Thanks for that Siwastaja,   my 12v,5v notation are battery terminals,  in that case.

I can see now that is a picture of 2 power sources in series.

It might not be a complete schematic (my retard drawing i mean) to go into a simulator,  but u can actually build it from that fine, its the full information...  if, you have a 12 v +- source and a 5v + source.

There is no 0v connection,  because the joke was I couldnt get 0v to work, because hunks of metal dont work as grounds, as weve been discussing, and have experimental proof for,  but i can get *5v* off a battery...   why would one work and not the other.
« Last Edit: March 16, 2020, 12:49:10 pm by krayvonk »
 

Online Zero999

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Re: connecting to 0 volts.
« Reply #34 on: March 16, 2020, 01:50:56 pm »
No, you can't really build it because it's ambiguous.

I entered it into LTSpice, guessing where the grounds and commons should go.

Firstly, consider the other side of each power supply is ground. It can be analysed as I described in my previous post. I added V4 and R3 to prove the potential divider is equivalent to a 500 Ohm resistor to 0V, as far as the 5V PSU is concerned. Note the currents are negative, because LTSpice shows them as the current is being taken from the PSU, i.e. the batteries are being discharged.
* ground problem 1a.asc (1.2 kB - downloaded 5 times.)


Secondly, assuming the other side of the 5V rail is ground and the 12V power supplies are floating, with the other sides connected to a different reference, hence the different symbol. No current flows out of the 5V rail, which lifts both 12V supplies up by 5V. This was what I assumed, when I initially replied to the thread.
* ground problem 1b.asc (0.97 kB - downloaded 5 times.)


Now let's change the 5V rail to 100V. The 12V rails shift up by 95V, giving 112V and 88V. I stuffed up on my arithmetic on my previous post.
* ground problem 1c.asc (0.97 kB - downloaded 5 times.)
« Last Edit: March 16, 2020, 01:54:37 pm by Zero999 »
 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #35 on: March 16, 2020, 01:57:43 pm »
Where do you guys learn all this stuff???   Why am I the odd one out.
 

Online Zero999

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Re: connecting to 0 volts.
« Reply #36 on: March 16, 2020, 02:13:59 pm »
Where do you guys learn all this stuff???   Why am I the odd one out.
School, college, university, books, work, the Internet etc.

Finally, if I draw the circuit, as you drew it, assuming the other sides of the power supplies are floating, the currents are all zero, because they're all open circuit. SPICE won't simulate it, because the voltages will all be undefined, as everything is floating, so I edited it in MS Paint.
 

Offline krayvonk

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Re: connecting to 0 volts.
« Reply #37 on: March 16, 2020, 03:37:42 pm »
Thats a limitation in my book...   I need to write my own simulator.  (laugh if you will...)
 

Online Siwastaja

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Re: connecting to 0 volts.
« Reply #38 on: March 16, 2020, 04:35:46 pm »
There needs to be a closed loop. Without that, current can't flow. Without current, you can't do much electronics.

Closed loop is a line of wire and components that you can follow, make a full lap, and end up where you started.
 

Offline Nerull

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Re: connecting to 0 volts.
« Reply #39 on: March 16, 2020, 05:49:58 pm »
Thats a limitation in my book...   I need to write my own simulator.  (laugh if you will...)


Perhaps learning basic electronics would be good start, first.

No simulator can fix your misunderstandings.
« Last Edit: March 16, 2020, 05:51:52 pm by Nerull »
 

Online Siwastaja

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Re: connecting to 0 volts.
« Reply #40 on: March 16, 2020, 06:09:44 pm »
Most simulators assume the basics are "right" and work improperly if they are not, not matching real-world results. SPICE simulators especially are pain-in-the-ass for total beginners.

If you want to learn by doing instead of reading (I recommend the combination of the both), play with the actual components instead: batteries, wire, lightbulbs, small DC motors, a multimeter. I started this way before I could read. Helps you get intuition so that wrong ideas won't stuck. The problem with reading is, many bookwriters suck in clear communication, and while technical details are plentiful and mostly right, stupid basic mistakes happen in the first chapters.
« Last Edit: March 16, 2020, 06:12:50 pm by Siwastaja »
 
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Online Brumby

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Re: connecting to 0 volts.
« Reply #41 on: March 16, 2020, 11:57:51 pm »
No, you can't really build it because it's ambiguous.

I entered it into LTSpice, guessing where the grounds and commons should go.

Firstly, consider the other side of each power supply is ground. It can be analysed as I described in my previous post. I added V4 and R3 to prove the potential divider is equivalent to a 500 Ohm resistor to 0V, as far as the 5V PSU is concerned. Note the currents are negative, because LTSpice shows them as the current is being taken from the PSU, i.e. the batteries are being discharged.
(Attachment Link)
(Attachment Link)

Secondly, assuming the other side of the 5V rail is ground and the 12V power supplies are floating, with the other sides connected to a different reference, hence the different symbol. No current flows out of the 5V rail, which lifts both 12V supplies up by 5V. This was what I assumed, when I initially replied to the thread.
(Attachment Link)
(Attachment Link)

Now let's change the 5V rail to 100V. The 12V rails shift up by 95V, giving 112V and 88V. I stuffed up on my arithmetic on my previous post.
(Attachment Link)
(Attachment Link)
My appreciation to Zero999 for taking the time to put this together (I just didn't have that yesterday) ... and to note that the word "assume" appeared in his efforts.  I was trying to avoid making assumptions.

There needs to be a closed loop. Without that, current can't flow. Without current, you can't do much electronics.

Closed loop is a line of wire and components that you can follow, make a full lap, and end up where you started.

This is the point I was making earlier - except this wording makes it extremely explicit.
 

Offline james_s

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Re: connecting to 0 volts.
« Reply #42 on: March 17, 2020, 12:12:14 am »
It is the whole circuit, do you need me to show you the application as well? :)

just think of the resistors as potentiometres,  and the battery connections are solid and unchanging.

There is error in the result, because of load theft on the potentiometres,  when you increase the power of "operand b" itll actually draw more current down the side from "operand a", so it would give you a more contrastive result than a correct subtraction.

I wished the bare "ground pole" (which is the low PotentialDifference battery...) would short away because its 100% loadless,  but I forgot both operands have a resistor/potentiometre so that wouldnt happen.   So it doesnt work that well anyway.

That's not the whole circuit though, you don't have a circuit, you just have some resistors connected to arbitrary voltages with no return path. Normally "ground" is implied in a circuit, and if this is the case then you have 3 voltage sources relative to this point called "ground" and your meter is also referenced to this point. This is not clear from your schematic though because it isn't drawn.

I'm not sure how you plan to write a simulator when you are missing a fundamental understanding of some of the most basic and rudimentary concepts of electricity. Spend a few hours reading about Kirchoff's laws and that should get you started. You are missing the very, very basic low level concepts and without grasping those you will never understand the rest. It's like trying to understand calculating the trajectory of a rocket without grasping how gravity and Newton's laws of motion work.
 


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