Author Topic: MH's ideal coil and voltage question (Read 487932 times)

poynt99 · « **Reply #1560 on:** July 05, 2016, 03:21:19 PM »

Quote from: tinman on July 05, 2016, 02:58:35 PM

I do not know,nor do i have the means to find out.

You have the ability to think and ponder, correct? Perhaps you could use your knowledge to surmise what the traces may look like? For example, would there be anything to "charge" if there were no capacitance? If not, then would that current bump be present?

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My point is this--
We would assume that we would not see this with an ideal coil,and we know we do have this situation with a non ideal coil,and so the two will not act in the same manor.

As far as i can see from bench tests,the CEMF dose not equal the EMF at T=0 ,with real world inductors--am i incorrect in saying that?,and if so,what is the initial current spike at T=0,if it is not the charging of coil capacitance ?.

Your point is understood and accepted. However, it seems you are missing the forest for the trees.

tinman · « **Reply #1561 on:** July 05, 2016, 04:08:30 PM »

author=poynt99 link=topic=16589.msg487809#msg487809 date=1467724879]

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You have the ability to think and ponder, correct? Perhaps you could use your knowledge to surmise what the traces may look like? For example, would there be anything to "charge" if there were no capacitance? If not, then would that current bump be present?

One could speculate that there would be no bump due to the charging of capacitance with an ideal coil.
But one would also wonder as to how that may effect the outcome of the results.
If we remove one part of a system,then it may just make the outcome a whole lot different than thought.

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Your point is understood and accepted. However, it seems you are missing the forest for the trees

An interesting saying,as without the tree's,there is no forest.

I know what your saying Poynt,and chances are you are right. But one thing has become of this so far,and that is,for the first time,i have seen the capacitance being charged in an inductor.

I would rather look at things far more closely, and observe everything that is taking place,rather than just look at the forest from afar.
Better to be amongst the trees i think,that way we see all that exist in the forest

Brad

poynt99 · « **Reply #1562 on:** July 05, 2016, 07:25:19 PM »

Quote from: tinman on July 05, 2016, 04:08:30 PM

One could speculate that there would be no bump due to the charging of capacitance with an ideal coil.
But one would also wonder as to how that may effect the outcome of the results.
If we remove one part of a system,then it may just make the outcome a whole lot different than thought.

One can also use their knowledge gained from prior experience to confidently predict certain outcomes.

MileHigh · « **Reply #1563 on:** July 05, 2016, 08:11:58 PM »

Quote from: tinman on July 05, 2016, 02:20:43 PM

My point is this.
At T=0,with regard to a real world inductor,the CEMF is not equal to the EMF,due to capacitance charging. This means that the ideal coil will react differently to that of a real world coil that has parasitic capacitance.

I think that you are making up one of your "ruel's" but unfortunately it doesn't make any sense. Even if you add a parasitic capacitance in parallel with an inductor model that consists of an ideal inductor with added wire resistance only, the CEMF will still be equal to the EMF. You have to think these things through.

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once again we see the current trace track the voltage trace,and for a short time,the current actually leads the voltage. This would mean a clear indication of capacitance being charged.

It does look like a capacitance being charged but you typically only talk about current leading the voltage in a case where the excitation is a repeating sine wave. You can even extend the concept and apply this for things like say a repeating square wave. But you are not in that territory at all. You are really just looking at the response to a single pulse and therefore you are misapplying the concept of current leading or lagging the voltage. It does not apply when you look at the response to a pulse.

Beyond that, you are simply leading yourself down a garden path. When you look at the scope shot the current does not "actually lead the voltage." All that you are seeing is that part of the current waveform is higher than the voltage waveform on the scope capture. You could easily change the gain settings on the scope and then the "current actually leading the voltage" would go away. One more time, you have to think these things through.

partzman · « **Reply #1564 on:** July 06, 2016, 04:48:12 PM »

Pursuant to simulating an inductance, I have some questions and comments.

In our ideal inductor of 5H, it is stated that Emf = Cemf when di = .8A/s. Can we then say di = Emf-Cemf?

It is interesting to read Wiki's definition of Counter-electromotive force and I quote in part "For example, the voltage drop across an inductor is due to the induced magnetic field inside the coil.[1][2] The voltage's polarity is at every moment the reverse of the input voltage.[1][3]" Is this not contradictory?

pm

picowatt · « **Reply #1565 on:** July 06, 2016, 06:48:16 PM »

Quote from: partzman on July 06, 2016, 04:48:12 PM

Pursuant to simulating an inductance, I have some questions and comments.

If you are going to try to simulate the PW model, you must simulate Cemf=L*di/dt

Quote

In our ideal inductor of 5H, it is stated that Emf = Cemf when di = .8A/s. Can we then say di = Emf-Cemf?

No...

But again, do you at least understand this negative feedback loop? If the problem is one of expression, that can be dealt with. But it does not materially change the model or its action, just the way of looking at it.

1. When CEMF<EMF, di increases.

2. As di=.8A/s, CEMF=EMF.

3. However, if CEMF=EMF, di<.8A/s

4. If di<.8A/s, CEMF<EMF

5. Loop to 1

What is it you are trying to do? "Understand" the feedback mechanism or just "describe" it mathematically in a form you can agree with?

It would help if I knew what you disagree with or do not understand.

If it is your desire to express the CEMF as a negative voltage, that can be done, but it was hoped that as I described it, the concept of the induced CEMF being a negative feedback mechanism would be readily understood.

Quote

It is interesting to read Wiki's definition of Counter-electromotive force and I quote in part "For example, the voltage drop across an inductor is due to the induced magnetic field inside the coil.[1][2] The voltage's polarity is at every moment the reverse of the input voltage.[1][3]" Is this not contradictory?
pm

Contradictory to what? In the model, are not the positive terminals of both the EMF and CEMF facing each other? That is, the polarity of the CEMF is such that it "is at every moment the reverse of the input voltage".

If you want to see the CEMF as a negative voltage, measure around the loop KVL style...

I have work related chores to attend to and have little time right now. But please do let me know whether it is the entire concept of CEMF being a negative feedback mechanism that is troubling you or just the desire to mathematically express the CEMF as a negative voltage.

PW

partzman · « **Reply #1566 on:** July 07, 2016, 12:23:49 AM »

Quote from: picowatt on July 06, 2016, 06:48:16 PM

If you are going to try to simulate the PW model, you must simulate Cemf=L*di/dt

No...

But again, do you at least understand this negative feedback loop? If the problem is one of expression, that can be dealt with. But it does not materially change the model or its action, just the way of looking at it.

1. When CEMF<EMF, di increases.

2. As di=.8A/s, CEMF=EMF.

3. However, if CEMF=EMF, di<.8A/s

4. If di<.8A/s, CEMF<EMF

5. Loop to 1

What is it you are trying to do? "Understand" the feedback mechanism or just "describe" it mathematically in a form you can agree with?

It would help if I knew what you disagree with or do not understand.

Well, I must admit that at this time, I do not believe I can simulate the PW model. I do understand the feedback loop but what you are saying in essence is that the function of inductance is dependent on the applied voltage and Cemf feedback. If so I disagree. I think the feedback is an effect that is the result of a deeper cause and that is flux interaction between windings with said flux generated by the current flowing in the wire due to the applied voltage source. Everything else follows this IMO.

Surely in 3) above you meant to say "if CEMF>EMF, di<.8A/s".

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If it is your desire to express the CEMF as a negative voltage, that can be done, but it was hoped that as I described it, the concept of the induced CEMF being a negative feedback mechanism would be readily understood.

Contradictory to what? In the model, are not the positive terminals of both the EMF and CEMF facing each other? That is, the polarity of the CEMF is such that it "is at every moment the reverse of the input voltage".

If you want to see the CEMF as a negative voltage, measure around the loop KVL style...

I don't wish the Cemf to be negative or positive. I am/was trying to generate a single expression (if possible) to simplify the simulation.

I still find the Wiki wording confusing, sorry!

Quote

I have work related chores to attend to and have little time right now. But please do let me know whether it is the entire concept of CEMF being a negative feedback mechanism that is troubling you or just the desire to mathematically express the CEMF as a negative voltage.

PW

I understand what you are stating and your description of the feedback mechanism. I do have a problem with it being the controlling factor of inductance as I stated earlier. So, I don't think I can really contribute anything useful to the matter from this point forward and my comments may be confusing without any substance to back them up.

Best to all.

pm

picowatt · « **Reply #1567 on:** July 07, 2016, 01:01:59 AM »

Quote from: partzman on July 07, 2016, 12:23:49 AM

Well, I must admit that at this time, I do not believe I can simulate the PW model. I do understand the feedback loop but what you are saying in essence is that the function of inductance is dependent on the applied voltage and Cemf feedback. If so I disagree. I think the feedback is an effect that is the result of a deeper cause and that is flux interaction between windings with said flux generated by the current flowing in the wire due to the applied voltage source. Everything else follows this IMO.

Surely in 3) above you meant to say "if CEMF>EMF, di<.8A/s".

Actually no.

If CEMF<EMF, di increases. Consider CEMF=0, at which time the full 4 volts is applied across the conductor and current rises rapidly. Even if CEMF=3.99volts, current would rise very rapidly (both the EMF and CEMF sources are considered ideal in the discussion)

If CEMF=EMF, current does not rise so di<.8A/s. (technically, di=0 would be true if CEMF=EMF. However, this condition also causes the CEMF<EMF, so I would not state di=0 when CEMF=EMF in an isolated statement. It is an unstable term in the feedback loop and would be confusing to state outside of that loop)

If the CEMF>EMF, the CEMF would tend to reverse the flow of current and the rate of change, di, would go negative as the current flow would be decreasing.

Due to the feedback mechanism, di is "trapped" at precisely .8A/s and cannot be greater or lesser than that amount. Any attempt by di to be greater or lesser than .8A/s will affect the CEMF such that di is forced to return to .8A/s.

We know, by the very definition of the Henry (1A/s thru 1H produces an EMF of 1volt that opposes the current that induced it) that the 5H inductor will generate a an EMF of 4 volts when .8A/s is flowing thru it.

That induced EMF will oppose the direction of the current flow that induced it, hence it is referred to as a CEMF. In all the models proposed, including yours, the CEMF polarity has been consistent, with the + terminals of the two representative sources facing each other.

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I don't wish the Cemf to be negative or positive. I am/was trying to generate a single expression (if possible) to simplify the simulation.

I still find the Wiki wording confusing, sorry!

I understand what you are stating and your description of the feedback mechanism. I do have a problem with it being the controlling factor of inductance as I stated earlier. So, I don't think I can really contribute anything useful to the matter from this point forward and my comments may be confusing without any substance to back them up.

Best to all.

pm

I had hoped that if you read my proposals for a simple simulation using either an arbitrary current source or another 5H inductor for a .8A/s current reference, that perhaps the action of the CEMF might become more clear.

Even if you do not intend to attempt a simulation, perhaps if you scratched out the proposed simulation circuit on paper it would help...

PW

tinman · « **Reply #1568 on:** July 07, 2016, 01:20:53 AM »

Quote from: partzman on July 07, 2016, 12:23:49 AM

Well, I must admit that at this time, I do not believe I can simulate the PW model. I do understand the feedback loop but what you are saying in essence is that the function of inductance is dependent on the applied voltage and Cemf feedback. If so I disagree. I think the feedback is an effect that is the result of a deeper cause and that is flux interaction between windings with said flux generated by the current flowing in the wire due to the applied voltage source. Everything else follows this IMO.

Surely in 3) above you meant to say "if CEMF>EMF, di<.8A/s".

I don't wish the Cemf to be negative or positive. I am/was trying to generate a single expression (if possible) to simplify the simulation.

I still find the Wiki wording confusing, sorry!

I understand what you are stating and your description of the feedback mechanism. I do have a problem with it being the controlling factor of inductance as I stated earlier. So, I don't think I can really contribute anything useful to the matter from this point forward and my comments may be confusing without any substance to back them up.

Best to all.

pm

I believe that what wiki is saying,is that the polarity of the CEMF voltage will cause a current to flow in the opposite direction to that of the source,and so there for,the polarity is opposite to that of the EMF,even though the polarity is the same

The confusion for me is,PW keeps assuming that the EMF will produce a current of 800mA/second,an so some how the CEMF induced current is less than this 800mA.

In a real world inductor,we have first a current flow induced from the EMF to charge the capacitance of the coil,and so at this point (T=0),the CEMF is not equal to the EMF,as a magnetic field is yet to be produced that creates the CEMF. Once capacitance is charged,the current drops back down to a 0 value,and then current starts to flow that produces the magnetic field that induces the CEMF.
So with a real coil,we have a small time delay between applied EMF ,and produced CEMF. This is enough time to create an offset between the EMF induced current,and the CEMF induced current.

With an ideal coil,we get no such offset,as there is no parasitic capacitance,and so to me,there is an instant reaction to any current that tries to flow as a result of the applied EMF,by the CEMF.
So i am still stuck as to how PW still insists that the EMF will win out in this battle,and produce a current flow greater than that of the CEMF induced current.

If at T=0,the EMF induced current flow value is 800mA/second,and at that very same instant the CEMFs induced current flow is also 800mA/second,then you have no current flow.
The very instant current tries to flow in one direction,it is counteracted against by a current trying to flow in the other direction,so how was it decided that the EMF induced current would win in this battle?,as it would seem to me that every action is met with an equal and opposite reaction.

Ideal or not,the current rise time could not be faster than the speed of light,and so the EMF induced current would have to start of with a value at !lets say for example! 1mA,and so at that very time,the CEMF induced current would also have to be 1mA. We know this current variation in time exist,as it has been denoted as rising at 800mA/second,and so that is less than 1mA per microsecond.
So why are we looking at the result at the 1 second mark?,why not at the instant of connection?.

Brad

synchro1 · « **Reply #1569 on:** July 07, 2016, 01:55:54 AM »

@Tinman,

Here's a quote from you:

"I believe that what wiki is saying,is that the polarity of the CEMF voltage will cause a current to flow in the opposite direction to that of the source,and so there for,the polarity is opposite to that of the EMF,even though the polarity is the same "

This is the point I tried to make to you on Luc's moderated thread that got me 86'd off this website!

poynt99 · « **Reply #1570 on:** July 07, 2016, 02:03:34 AM »

I'm returning to some cool audio design.

picowatt · « **Reply #1571 on:** July 07, 2016, 02:45:38 AM »

Quote from: poynt99 on July 07, 2016, 02:03:34 AM

I'm returning to some cool audio design.

What are you makin'?

Perhaps it will have a tone control circuit using, as is often done, a simulated inductor circuit, i.e., a "gyrator" circuit...

After all this, I can't imagine having to explain that one...

PW

poynt99 · « **Reply #1572 on:** July 07, 2016, 03:20:48 AM »

Haha,

I refreshed my memory about gyrators the other day as another idea to perhaps help elucidate on the inductor discussion here, but I soon came to my senses

Breaking new ground with a guitar amplifier design. MOSFETs rather than tubes.

Could use your help with a few advanced questions if you wouldn't mind.

picowatt · « **Reply #1573 on:** July 07, 2016, 03:35:10 AM »

Quote from: poynt99 on July 07, 2016, 03:20:48 AM

Haha,

I refreshed my memory about gyrators the other day as another idea to perhaps help elucidate on the inductor discussion here, but I soon came to my senses

Breaking new ground with a guitar amplifier design. MOSFETs rather than tubes. Could use your help with a few advanced questions if you wouldn't mind.

.99,

I always wanted to try switching out the outputs in the larger bass and guitar amps with MOSFET's. 6L6/6550?.

I love analog audio design, I miss the old discrete stuff, like Flickinger, API and Sphere consoles, etc (with the Sphere Eclipse C with their SPA62 discrete opamps and passive EQ circuits sounding the best in my opinion). I also miss discrete analog tape recorders like the Ampex 440 and MM1200 series. But the current 2" tape prices and availability, wow... Anyway, those were the days.

As for your project, you could ask but I am now on page 28 and counting of a document for a client and I have not even gotten to inserting graphs or images, and it was expected over a week ago.

So, the timing could not be worse.

There is just never enough fun...

PW

MileHigh · « **Reply #1574 on:** July 07, 2016, 03:36:59 AM »

It has to be an Old School gyrator, see attached. If the gyrator is post-1950 then it is suspect and could have been corrupted by the PTB.

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Author Topic: MH's ideal coil and voltage question (Read 487932 times)

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