current returning to a different source

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rattus said:
Rick,
............Second, One has to be pretty full of himself to argue with a professor of physics from MIT!
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Well unless you happen to be this MIT professor, then it is ill advised for you to be putting words into his mouth! :mad: Unless you carry his credentials, you have no right to quote his credentials! Speak of your own credentials, not of someone else's. I am an electrical engineer, and I will speak for myself, and I will stand up for myself if I am wrong. If I am wrong, then I will publicly apologize on this forum for being wrong.
 
Rick, I see exactly what you are saying and I agree with you. I think the issue arises when you speak of:

"If you can maintain a voltage difference between these two points, then you will have a current flow (assuming a conductor exists)."


I am going to say that essentially, this is the definition of a voltage source, and therefore the "assumed conductor" is actually creating a closed circuit from one side of the source to the other.

So basically we are arguing semantics.

Assuming there are a finite number of electrons and protons in the universe, maintaining a voltage difference between two points can't be sustained. There has to be some interchange of electrons between the positive point and the negative point and outside of the path created by the conductor, which makes the two points become a single voltage source.

Edit: Clarification of thought.
 
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Rick Christopherson said:
If I am not mistaken, the raw definition of Ohm's law states that current will flow between any two points with a voltage difference, and the rate of current flow will be proportional to the resistance between these two points. There is nothing in Ohm's Law that says current has to return to the source before it can flow. It is simply a relationship between voltage, resistance, and current.
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To maintain that voltage, one must apply a battery or an AC source--both of which provide a closed circuit. One might also pump a current through the resistance with a current source which must also complete the circuit.

Now consider an open transformer secondary which is ideal except for some series resistance, Rs. The equivalent circuit will be an EMF in series with Rs. There will voltage between the terminals, but zero current. Then the drop across Rs is also zero because the current is zero. Ohm's Law holds!

Lightning is so far removed from this discussion that we shouldn't even mention it.

Archie Bunker's lawyer says "don't argue with a station wagon full of nuns." I say, "don't argue with a professor of physics from MIT"!
 
Rick Christopherson said:
Well unless you happen to be this MIT professor, then it is ill advised for you to be putting words into his mouth! :mad: Unless you carry his credentials, you have no right to quote his credentials! Speak of your own credentials, not of someone else's. I am an electrical engineer, and I will speak for myself, and I will stand up for myself if I am wrong. If I am wrong, then I will publicly apologize on this forum for being wrong.
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Nonsense! I took the words from his mouth or rather his book. Verbatim quotes, properly cited, are freely used in all of science, and that is what I have done. One can find essentially the same passage in any number of texts on basic electricity. Science would be in a sad state if we couldn't quote references.
 
This thread is making my head hurt. LOL
I'am in no way shape or form an engineer or even close to understanding the theories you guys are throwing out here. But I do like it!
Beats the ground up or ground down threads.
 
rattus said:
I took the words from his mouth or rather his book.....
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I don't care whether you took words from someone else's mouth or how closely you quoted them. If he/she is not present in this discussion, then it makes no difference. You said I challenged an MIT professor, when he was not here to discuss this.

You are NOT an MIT Professor so you do not have the right to speak as though you have this authority! :mad: :mad: :mad:

Speak for yourself, or don't speak at all!

I am not saying I could stand up to an MIT professor, and I would probably get my arse handed to me if I tried. However, you are not an MIT professor, and should not speak as though you carry his credentials.
 
I say the light is off

I say the light is off

You are center taping the batterys much like a pole mount transformer. This is just my humble opinion of course there is no reference that I can see. Maybe ground the jumper and take the light off the other side. Better be a 24volt lamp tho
 
Ludicrous!

Ludicrous!

Rick Christopherson said:
I don't care whether you took words from someone else's mouth or how closely you quoted them. If he/she is not present in this discussion, then it makes no difference. You said I challenged an MIT professor, when he was not here to discuss this.

You are NOT an MIT Professor so you do not have the right to speak as though you have this authority! :mad: :mad: :mad:

Speak for yourself, or don't speak at all!

I am not saying I could stand up to an MIT professor, and I would probably get my arse handed to me if I tried. However, you are not an MIT professor, and should not speak as though you carry his credentials.
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Fact is, the quote from Dr. Sears punches a big hole in your claim, and you are trying to hide that fact with an inane argument. Furthermore, according to your thinking we cannot quote Ohm, Joule, Tesla, Einstein, Faraday, Henry, and dozens of others who have developed valid theories over the years. You are the first ever to tell me I cannot uses references to prove my point.

Anyone who claims to be an engineer ought to know that references are routinely used to prove or disprove a point. These fellows were smarter than most of us, and since we can't bring them to the Forum, we quote them. We don't claim to carry their credentials, we just repeat what they said.

Why don't you just defend your position instead of throwing tantrums? If you disagree with Sears, say so, and back up your argument in a civil manner. That is what this Forum is all about.
 
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It's like this:

It's like this:

qcroanoke said:
This thread is making my head hurt. LOL
I'am in no way shape or form an engineer or even close to understanding the theories you guys are throwing out here. But I do like it!
Beats the ground up or ground down threads.
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It boils down to the fact that the switch has to be closed before we have current!
 
crossman said:
Assuming there are a finite number of electrons and protons in the universe, maintaining a voltage difference between two points can't be sustained. There has to be some interchange of electrons between the positive point and the negative point and outside of the path created by the conductor, which makes the two points become a single voltage source.
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There is another way to get the interchange of electrons. Reverse the direction periodically. Let's say we can devise a source of voltage that alternates from one direction to the other periodically. Then let's connect a wire from one side to a large plate to collect electrons. Then connect a wire from the other end to another large plate close to the first, but not connected to it. When the voltage reverses, the electrons flow form one plate to the other.

Let's call the voltage source an "alternating current generator" and the plates a "capacitor" because they have the capacity to hold a charge.:grin:
 
Rick Christopherson said:
If I am not mistaken, the raw definition of Ohm's law states that current will flow between any two points with a voltage difference, and the rate of current flow will be proportional to the resistance between these two points. There is nothing in Ohm's Law that says current has to return to the source before it can flow. It is simply a relationship between voltage, resistance, and current.
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Correct, it is Kirchoff's Voltage Law which is derived from Georg Ohm:
The directed sum of the electrical potential differences around a closed circuit must be zero.
(Otherwise, it would be possible to build a perpetual motion machine that passed a current in a circle around the circuit.)
 
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mull982 said:
What happens when current originating from from one source (transformer) returns on a nuetral to a different source (different transformer)?
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let met start by saying I am not an engineer. Also, I am not an expert in the mathematics of this issue.

Here is how I see this based on the limited knowledge I have developed over my career.

Maybe you were mistaken about the statement you made above??



Current flowing from source-1 can travel along a conductive path through another conductor from a different source-(2), if there is some connection between the conductors of source-1 and source-2.

But...
I do not believe source-1 will push current along any conductive path to return to source-2. The current does not want to go from source-1 to source-2 regardless...it would only flow from source-1 THROUGH source-2 if it was flowing along a path between both sources.

If source-1 current were to flow from source-1 through a conductive path to source-2, there would be some kind of problem developing during this process.


"Say I have a 120V single phase transformer-1 which is sending current out via the hot leg of transformer-1 to a device, however the the nuetral coming off of the device does not return to the neutral of transformer-1, but rather the neutral of a different transformer I'll call transformer-2"


This is not a difference of potential creating this current flow, it would be current flow somehow finding a path through the source-2 as it heads back to source-1.



Now, if you could prove this to be otherwise, I would be very interested to see how.


Remember, the world was once thought to be flat, until someone was able to circumavigate around the globe without falling off. :wink:
 
Pierre, your post is right on target. And, in a typical situation of one service or one buildiing with multiple xfmrs, most likely the completed paths you mention would exist through the system bonding jumpers and the equipment grounding conductors.
 
My input:


In the OP, no current would flow unless the systems are interconnected. Other than capacitive impedances, it's an open circuit.

Rick's statement is correct. The flaw is that there will not be a potential difference between two points without a closed circuit.

Lightning is like a charged capacitor. It's not a practical power source.* Static discharge is not useable steady-state current.


* Back to the Future aside.
 
LarryFine said:
Rick's statement is correct. The flaw is that there will not be a potential difference between two points without a closed circuit.
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Rick's statement is correct?...!!!

I say it is incorrect (...to the nth degree, actually). His statement uses the term "voltage" loosely to mean E in Ohm's equation: E = I ? R.

One has to understand the contrast between the terms "electrical potential difference" and "electromotive force". Ohm's equation uses the latter, and has no consideration for electrical potential difference (i.e. voltage when no current flows).

http://en.wikipedia.org/wiki/Voltage

[Edited to delete an incorrect statement]
 
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Smart $ said:
Rick's statement is correct?...!!!
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You missed my point; I'm agreeing with you.

With the setup mentioned in the OP, there would be no potential difference (capacitive coupling aside - I mean with the source impedance (i.e., current capability) to be useful) between the two secondaries, unless there is an interconnection, such as the common bonding.

Transformer secondaries are SDS's and, until bonded to a common conductive pathway, they are isolated systems. That's the whole idea behind non-grounded power circuits in operating rooms and such; a single contact will not flow enough current to do any harm.

Rick's statement about there being a potential difference between two unbonded systems is a fallacy. Where he got a wiggy with leads long enough to reach the moon is beyond me. :roll: I'd like to know whether the moon is positive or negative relative to 'earth'.
 
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