MH's ideal coil and voltage question

[tinman]

Brad:

Are you a lost soul or are you a man with the conviction to stand up for what you say and back it up with a logical argument?  Put meaning to your statements and show conviction or just be a space cadet?  Which one is it going to be?

Let's look at two cases.

1)  The unanswered request for you to put substance behind your claim with an actual example.

The ball is now in your court.  You say that the CEMF must be lower than the EMF for current to flow?  I have never seen any concrete examples of that from you.  Now is the time.  Show us some examples where the CEMF is lower than the EMF with all the specifics and all of the numbers crunched to explain how much current flows.

Forget about the motor example, and keep it simple and use a coil.  Give some examples providing all of the specifics and the EMF and CEMF values, the current flow, the whole nine yards.

You say the correct model is that the CEMF is less than the EMF?  Go ahead and give some examples with all of the details laid out so we can see if your model works or not.

2)  Who really has lost their marbles?

You have a one-volt voltage source connected across a one-Henry inductor, which gives you one amp of current per second flowing through the inductor.

So where is the EMF and the CEMF?  The one-volt voltage source is the EMF.  The CEMF is the one amp of current per second flowing through the inductor causing a one-volt voltage drop across the inductor.

The one-volt voltage drop across the inductor is the CEMF.   Look at that, the EMF and the CEMF are equal and opposite, and current flows through the inductor.

That's the real deal and that's the way it is modeled.

There is no difference between the EMF and the CEMF and current flows through the inductor.

So Brad, you allege that I have "lost my marbles" with respect to the example above.  Then you break down that example and show us exactly where and why it is wrong.  If you can't do that then you are the one that has lost your marbles.

MileHigh

This one volt voltage drop across the inductor is horse radish,and also makes things more confusing than they need to be.
The inductor dose not cause the voltage drop,as the voltage applied across the inductor by the source is exactly what will be across the inductor. You might as well say there is a 1 volt voltage drop across a 1 volt battery--how stupid dose that sound

MH
You are doing nothing but adding some sort of idiotic confusion to everything everyone has learned.
I dont give a rats ass what you say,if the CEMF is equal to the applied EMF,then no current will flow through that inductor.
And this cods wallop about a resistor creating an equal and opposite CEMF to that of the applied EMF,is nothing short of insane.

You say that the CEMF must be lower than the EMF for current to flow?

Yep,as that is what stops the current through an inductor shooting straight up to a maximum value determined by the inductors winding resistance,when a voltage is placed across.
Same with water flowing through pipes-as i stated before. Once the head pressure pushing back against the pump equals the pumps maximum pumping pressure,there will be no water flow.
The pressure is your voltage,and the water flow rate is your current.


Say what you will MH,but i am no longer interested in what you have to say.


Brad

[hoptoad]

snip...
There is no difference between the EMF and the CEMF and current flows through the inductor.
snip...
MileHigh

When an inductor is first connected to a Voltage Source at time=0 and counting, the EMF and CEMF are EQUAL and their is NO current flow.

At end of TC 1 (TC = time constant of the inductor) the CEMF will be .37 of The EMF and supply current is flowing.
At end of TC 2 the CEMF will be .14 of The EMF and supply current is flowing.
At end of TC 3 the CEMF will be .5 of the EMF and supply current is flowing.
At end of TC 4 the CEMF will be .2 of the EMF and supply current is flowing.
At end of TC 5 the CEMF will be .0 of the EMF = non existent and supply current is flowing.

Any moment after that, the current through the inductor will be steady, the EMF will be steady and there will be NO CEMF.

MH, for someone who insists that others use the correct nomenclature when referring to circuitry, you seem to be pretty liberal with how you apply it yourself. Voltage drop across a component is not CEMF. EMF is not CEMF. Constant EMF is sustainable, constant CEMF is not.

Here's a link showing the relationship of CEMF in a series LR circuit, with the resistance external to the inductor and the presumption of an ideal inductor. Step through the exercise and answer the questions.

https://www.wisc-online.com/learn/career-clusters/stem/ace5903/an-inductor-opposing-a-current-change

Cheers

[tinman]

 author=poynt99 link=topic=16589.msg486943#msg486943 date=1466638667]


In terms of KVL, it holds fine, and the "drop" across the inductor is determined by the voltage source, just as in the case for the resistor, but it is NOT the cemf, if indeed emf is equated with voltage.

Is this explanation crazy? Perhaps, but I've not seen any other that makes sense to me.

Isn't an inductor very much like a frequency-dependent resistor? If so, then maybe it makes sense for it to have a voltage drop across it.

How can it be Poynt. A resistor has no inductance,produces no magnetic field,and the value of resistance in a resistor dose not change over time.

Kirchhoff's KVL always holds, so the problem is perplexing, especially in light of the descriptions on self induction, whereby an opposing "self-induced emf" results from the changing flux in the coil. "Opposing" in what manner?

Opposing as in-producing a current that flows in opposition to that of which the applied EMF is trying to create.
As we discussed earlier,it is what stops the current going straight to a maximum value,once a voltage is placed across that inductor--what else would limit the rate of current increase in that inductor when a voltage is placed across it,if it is not the self induced EMF?.

One argument is that if the EMF and CEMF were equal, no circuit current would flow. I think we may be arguing with an incorrect assumption in mind. We can envision the voltage source and the induced emf as two generators back to back, but is this accurate?

No,that would not be accurate as far as i am concerned.
The applied EMF would be seen as a prime mover,and the self induced EMF(CEMF) would be the generator attached to the prime mover. The load drawn from the generator could be seen as the CEMF,as there is always losses,the CEMF (power dissipated in load),will always be less than the power being supplied to the generator by the prime mover-->(or we may see something different at the other place  )

A voltage source and a resistor in parallel also have voltages that are back to back, yet current flows.

A resistor is not a voltage source,and has no voltage across it until such time one is applied to it from a voltage source. At that point in time,the resistor now becomes a resistive heater-nothing more.

The self-induced emf is present, but it is perhaps not what we might expect. When we use the term "emf" we expect it to mean there is or will be a resulting measurable voltage. When the voltage source is connected and the magnetic field begins building, the coil immediately starts inducing a cemf across its terminals. The coil has now become a generator; but there is a "twist". The load seen by the coil's terminals is the voltage source, and it would appear as a short circuit to the coil.

The voltage source will not be seen as a load,as the self induced EMF is less than the applied EMF,due to transformer losses,and there for,a potential difference still exists,and the higher potential is the voltage source. So the inductor is still seen as the load,because it has the lowest value of the two potentials
If the self induced EMF was equal to the applied EMF,then there is no potential difference between the two,and current will not flow unless there is a potential difference.

I made a statement a few posts back in that an induced current always has an associated induced voltage. I retract that and restate it this way: An induced current usually has an associated induced voltage. The fact is that a coil can have a current induced in it, even if the coil is shorted. This I believe is the scenario with the self-induced emf and current with our simple voltage source and inductor.

Yes,this was told to us on this thread by verpies many pages back,and some others here decided to tell him to stop confusing the subject at hand,by introducing things not associated with the question.
But now we have seen a full circle,and we are right back to the point verpies was making

So I am saying that the cemf induced in the coil goes to 0V, while the self-induced opposing current goes to some value, determined by the inductance and rate of flux change.

Is that the case?-im not sure.
If the CEMF value is 0,then how can a current be produced without voltage,when that coil(as discussed above)is not an ideal coil with an ideal short across it's terminals. Only an ideal coil with an ideal wire across it's terminals will allow for a current to flow through it,without a voltage across it.
Has anyone ever wound a coil with a center tap,and measured the voltage across half of the inductors winding's,while being subjected to a rising and falling current--will it be equal to 1/2 of the applied EMF?.


Brad

[tinman]

 author=hoptoad link=topic=16589.msg486958#msg486958 date=1466674702]

At end of TC 1 (TC = time constant of the inductor) the CEMF will be .37 of The EMF and supply current is flowing.
At end of TC 2 the CEMF will be .14 of The EMF and supply current is flowing.
At end of TC 3 the CEMF will be .5 of the EMF and supply current is flowing.
At end of TC 4 the CEMF will be .2 of the EMF and supply current is flowing.
At end of TC 5 the CEMF will be .0 of the EMF = non existent and supply current is flowing.

It is good to see there is some one else that is not falling for MHs gobble doc.

But now 2 questions for you Hoptoad.
1-why dose the magnetic field that is inducing the CEMF,slowly decrease in change over time in an inductor from T=0-->moment of the applied voltage across the coil.
2-why is the CEMF equal to the applied EMF at the moment the voltage is placed across the coil?.

MH, for someone who insists that others use the correct nomenclature when referring to circuitry, you seem to be pretty liberal with how you apply it yourself.

As i have said many times,MH changes things when it suit's his needs.
Do as i say--not as i do.

Voltage drop across a component is not CEMF. EMF is not CEMF. Constant EMF is sustainable, constant CEMF is not.

Indeed.

Here's a link showing the relationship of CEMF in a series LR circuit, with the resistance external to the inductor and the presumption of an ideal inductor. Step through the exercise and answer the questions.

I doubt that will happen. MH is on a !!MH!! is right saga,and nothing gets in the way.


Brad

[Johan_1955]

But now 2 questions for you Hoptoad.
1-why dose the magnetic field that is inducing the CEMF,slowly decrease in change over time in an inductor from T=0-->moment of the applied voltage across the coil.
2-why is the CEMF equal to the applied EMF at the moment the voltage is placed across the coil?.

Brad, you know already why, because you'''re did demonstrate it before, its the change!

And Change we need all: Europe complete HOPEFULLY for a