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### Author Topic: MH's ideal coil and voltage question  (Read 413047 times)

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #45 on: May 09, 2016, 11:23:45 AM »

Just answer the question.

I have answered the question many times.
Where are you reading?.

Brad

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #46 on: May 09, 2016, 11:34:55 AM »

Just answer the question.

Here is an idea John.
Instead of posting pictures of your farm animals,and non related comments--post your answer to the question here on this thread

Brad

#### Magneticitist

• Full Member
• Posts: 131
##### Re: MH's ideal coil and voltage question
« Reply #47 on: May 09, 2016, 12:01:06 PM »
I think the confusion lies in the general ridiculousness of the intended point.
The question is apparently geared to asses your knowledge of circuit operation by seeing how institutionalized you are regarding EE fundamentals as they are taught in a classroom setting.
no matter the logic you provide, until you work out some mathematical answer in detail based upon the numbers given your answer will not be considered. If you worked out the math to please them it would be pointless because as you have already stated you are in disagreement with the general nature of the question.

it's kind of like walking up to a mechanic who can take an engine apart and put it back together in better working condition than it started and saying "hey, work out how long this engine is going to last in minutes assuming I drove it 24hrs a day at at 50 mph, and there's no friction anywhere in the mechanical operation.. do it on paper and show me your entire work... oh? you can't? you clearly have no idea what you're doing then and should probably learn how to use a wrench before putting that engine back together"

MH and others want the question to be answered in the same form it would if you were a student in their EE class and it was assigned as a piece of homework. I'm not entirely sure the specifics of what they even want worked out, but I'd imagine a detailed explanation of the near characteristics of the coil over a scale of time given L is 5H. but is that even a common kind of EE question the way it was asked?  Right now I'm in the position of just being curious as to how they want the question answered. I feel like I can actually learn something from this exercise but it's being made more difficult than it needs to be.

#### minnie

• Hero Member
• Posts: 1244
##### Re: MH's ideal coil and voltage question
« Reply #48 on: May 09, 2016, 12:37:34 PM »

I don't want to spoil the fun, you'll get there in the end!
John.

#### wattsup

• Hero Member
• Posts: 2606
##### Re: MH's ideal coil and voltage question
« Reply #49 on: May 09, 2016, 01:00:09 PM »
Yes, all this does not detract from the ideal voltage source not being able to drop to anything else but its ideal voltage even in time. There would not be an eventual drop to 0 volts because the source would not care about an ideal inductor in any case, infinity or not. So............. even if the current rose to infinity and the inductor was totally destroyed, you would still have your source voltage unchanged. And there in lies the chicken and egg rub.

As well, you can analyze this until the cow jumps over the moon, but you will still not know what actually happens inside a coil and @MH, that includes you. Just because you can rationalize or try to rationalize these mind games, not one iota will be discovered on the coils true function, you are still stuck with only the mind effect.

Actually this is a good comparison for me because in SC current is the number of atoms active in energy conveyance and voltage is the depth at which conveyance occurs. Put 1 volt in a 5H coil that has a cvr tapped in the coil center and wait. The current having a finite number of atoms in the inductor, ideal or not, would be the limiting factor so you would not have any need to ponder ideal conditions to actually know what is happening inside your coil. Hence why I asked the question of wire gauge tables not defining their complete tests. Meanwhile you guys would still be scratching your heads wondering how a coil can handle infinite current.

So the question for you guys is simple. How can an ideal voltage provide infinite current. That is like saying a 46AWG wire should be able to render an infinite AWG wire red hot for infinity. hahaha And this is the same EE that calls OUers out-of-the-box crazy.

Maybe it's better to just chew on ideal gum with ideal jaws.

wattsup

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #50 on: May 09, 2016, 01:43:25 PM »
I think the confusion lies in the general ridiculousness of the intended point.
The question is apparently geared to asses your knowledge of circuit operation by seeing how institutionalized you are regarding EE fundamentals as they are taught in a classroom setting.
no matter the logic you provide, until you work out some mathematical answer in detail based upon the numbers given your answer will not be considered. If you worked out the math to please them it would be pointless because as you have already stated you are in disagreement with the general nature of the question.

There is nothing ridiculous about the intended points.  One point is to understand how an inductor works.  Another point is to be able to look at a schematic diagram and have a better preliminary sense of what what might be going on in the schematic.  Another point would be to be better able to design a circuit to do what you want it to do.  Another point would be to be better able to analyze a circuit that you have built.   Another point would be to be able to look at a scope trace as a passive observer vs. looking at a scope trace and relating it directly back to your circuit and understanding the waveform and why it is shaped the way it is.

Who says you have to give a mathematical answer for starters?  Why not just try to answer the question on a conceptual level for starters and then see if you can move on to a more formal answer?  The field is entirely wide open to you but I am not seeing much movement on that field.

On the other thread I clearly showed you how close an ideal inductor can be to a real-world inductor in an actual working circuit.  I showed you that ideal voltage sources are available right now, and anybody can play with one.

What I an seeing from you so far is that you are just blindly believing what Brad is saying.  The problem is that Brad is wrong.  So why don't you try to brainstorm and come up with something new?

The simple truth is this:  Brad has stuck with his wrong answer for a few days.  Instead of sticking to the wrong answer he could have been researching this stuff over the past few days and who knows he could have already made a breakthrough and then he could have started moving towards the actual answer.

I will repeat, this question is valid and very important if you want to experiment with coils and make pulse motors, the whole nine yards.  I admit it's a bit stark to come face to face with the fact that you play with coils all the time on your bench but you don't understand how they work.  Do do you remain sour and suck on bitter lemons all day, or do you try to turn lemons into lemonade?

Certainly, just refusing to do anything except repeat the same thing is not productive.

MileHigh

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #51 on: May 09, 2016, 01:43:44 PM »
I think the confusion lies in the general ridiculousness of the intended point.
The question is apparently geared to asses your knowledge of circuit operation by seeing how institutionalized you are regarding EE fundamentals as they are taught in a classroom setting.
no matter the logic you provide, until you work out some mathematical answer in detail based upon the numbers given your answer will not be considered. If you worked out the math to please them it would be pointless because as you have already stated you are in disagreement with the general nature of the question.

it's kind of like walking up to a mechanic who can take an engine apart and put it back together in better working condition than it started and saying "hey, work out how long this engine is going to last in minutes assuming I drove it 24hrs a day at at 50 mph, and there's no friction anywhere in the mechanical operation.. do it on paper and show me your entire work... oh? you can't? you clearly have no idea what you're doing then and should probably learn how to use a wrench before putting that engine back together"

MH and others want the question to be answered in the same form it would if you were a student in their EE class and it was assigned as a piece of homework. I'm not entirely sure the specifics of what they even want worked out, but I'd imagine a detailed explanation of the near characteristics of the coil over a scale of time given L is 5H. but is that even a common kind of EE question the way it was asked?  Right now I'm in the position of just being curious as to how they want the question answered. I feel like I can actually learn something from this exercise but it's being made more difficult than it needs to be.

Like i said,i dont think MH thought about his question very well when he included ideals in it.

Do we even have an inductor in the question?.
Well from an EEs view ,they may think they do,but from an outsiders view,there may be no inductor at all.

What are the properties of an ideal inductor?
An ideal inductor has no resistance,no capacitance,but only inductance
How can it have inductance if it has no resistance?

Well before the EE guys go--what the hell are you talking about,lets look at the meaning of resistance and inductance.
Resistance-->Resistance is the friction in an electrical circuit that controls the flow of current
Inductance-->   Inductance is typified by the behavior of a coil of wire in resisting any change of electric current through the coil

So a resistor controls the flow of current,and inductance resist any change in current. So it would seem that the inductor also tries to control the flow of current by resisting any change to it.
So inductance is a resistance,and an ideal coil has no resistance.
So dose this mean that it has no inductance?

Quote
MH and others want the question to be answered in the same form it would if you were a student in their EE class and it was assigned as a piece of homework.

Im not interested in there !theoretical! answers,im looking for the correct answer to the question.

All circuits are modeled using a resistor in series with the ideal inductor,so as to represent real world inductors. We need to model this circuit without the resistor,and i know just the man for the job.

Poynt
This will be one of very few times you hear me say this
Can you use your sim to model the circuit
I believe you have tried this before
Now,you have said on many occasions that the sim will produce actual result's,so lets see it produce some results regarding MHs ideal inductor with an ideal voltage across it-->lets see what happens.

No need to post the answer--just tell us if your sim was able to show real world results based around MHs parameters--that being a 5 Henry ideal coil,with a 4 volt ideal voltage across it for 3 seconds-->the first part of the cycle in MHs question.

Brad

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #52 on: May 09, 2016, 02:00:34 PM »
There is nothing ridiculous about the intended points.  One point is to understand how an inductor works.  Another point is to be able to look at a schematic diagram and have a better preliminary sense of what what might be going on in the schematic.  Another point would be to be better able to design a circuit to do what you want it to do.  Another point would be to be better able to analyze a circuit that you have built.   Another point would be to be able to look at a scope trace as a passive observer vs. looking at a scope trace and relating it directly back to your circuit and understanding the waveform and why it is shaped the way it is.

Who says you have to give a mathematical answer for starters?  Why not just try to answer the question on a conceptual level for starters and then see if you can move on to a more formal answer?  The field is entirely wide open to you but I am not seeing much movement on that field.

What I an seeing from you so far is that you are just blindly believing what Brad is saying.  The problem is that Brad is wrong.  So why don't you try to brainstorm and come up with something new?

The simple truth is this:  Brad has stuck with his wrong answer for a few days.  Instead of sticking to the wrong answer he could have been researching this stuff over the past few days and who knows he could have already made a breakthrough and then he could have started moving towards the actual answer.

I will repeat, this question is valid and very important if you want to experiment with coils and make pulse motors, the whole nine yards.  I admit it's a bit stark to come face to face with the fact that you play with coils all the time on your bench but you don't understand how they work.  Do do you remain sour and suck on bitter lemons all day, or do you try to turn lemons into lemonade?

Certainly, just refusing to do anything except repeat the same thing is not productive.

MileHigh

Quote
On the other thread I clearly showed you how close an ideal inductor can be to a real-world inductor in an actual working circuit.  I showed you that ideal voltage sources are available right now, and anybody can play with one.

No such voltage or inductor exist--not even close.

The fact is MH,and this is an absolute fact,you cannot back up your answer with a real world test to show you are correct.
There is no such thing as an ideal inductor,nor is there any such thing as an ideal voltage.

An ideal inductor has no resistance,and inductance it self produces resistance-a resistance to the change in current. So an ideal inductor dose not exist for that very reason,and there for your question cannot be answered-well maybe in MH fairy land.

An ideal voltage also dose not exist. There is no device that can provide an infinite amount of current to maintain an ideal voltage across a dead short that is also ideal-being a short that will never collapse under any load.

"Can God create a stone so heavy that even God is not strong enough to lift it?" God, being almighty, should be able to create this stone but if He does, he cannot move it meaning he is not almighty. However, if God cannot create this stone, the same problem arises.

Brad

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #53 on: May 09, 2016, 02:00:46 PM »
Yes, all this does not detract from the ideal voltage source not being able to drop to anything else but its ideal voltage even in time. There would not be an eventual drop to 0 volts because the source would not care about an ideal inductor in any case, infinity or not. So............. even if the current rose to infinity and the inductor was totally destroyed, you would still have your source voltage unchanged. And there in lies the chicken and egg rub.

As well, you can analyze this until the cow jumps over the moon, but you will still not know what actually happens inside a coil and @MH, that includes you. Just because you can rationalize or try to rationalize these mind games, not one iota will be discovered on the coils true function, you are still stuck with only the mind effect.

Hence why I asked the question of wire gauge tables not defining their complete tests. Meanwhile you guys would still be scratching your heads wondering how a coil can handle infinite current.

So the question for you guys is simple. How can an ideal voltage provide infinite current. That is like saying a 46AWG wire should be able to render an infinite AWG wire red hot for infinity. hahaha And this is the same EE that calls OUers out-of-the-box crazy.

Maybe it's better to just chew on ideal gum with ideal jaws.

wattsup

Lots of unproductive sour grapes.  You have got to be kidding about the "mind games."  The intention behind this question is to understand how a coil works in the real world.  For many experimenters it's possible that mastering this will open up a whole new world of true understanding for them, and instead of just being passive builders and observers, they will become active designers and analyzers.  What's the classic question among builders?  "What wire gauge and how many turns?"  They think that if they are mindless replicators then some magic will happen.  For a given project, who says the wire gauge is that important?  For a given project, who says the number of turns is that important?  Well if you have no clue you may as well just replicate and do what you are told to do, right?

The issue of "infinite current" is irrelevant.  The question of a certain wire gauge getting too hot at a certain current level is irrelevant.

There was a time when I explained to some beginners that the simple model for a battery that you use every day on your bench is an ideal voltage source in series with a resistor.  That explains why the battery voltage drops under load.  Look at that, an appearance of the dreaded ideal voltage source.  They were aghast just by the notion of "There is a resistor inside the battery!!??"  So for some people it's "radical" to actually try to understand how an inductor works.  The wiser people will want to understand this and they will be able to apply it to the work they do on their bench.

MileHigh

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #54 on: May 09, 2016, 02:11:21 PM »
Quote
No need to post the answer--just tell us if your sim was able to show real world results based around MHs parameters--that being a 5 Henry ideal coil,with a 4 volt ideal voltage across it for 3 seconds-->the first part of the cycle in MHs question.

The sim will work perfectly and I am glad that you don't want to see it.  The way you have to "see it" is to use your intellect to understand how an inductor works.

You are clearly still stuck like glue to your mistake.  The only question is what do you do?  Do you stick it out and refuse to explore other options until at the end you are spoon fed the answer?  If you agree the answer is correct then you will have a rather embarrassing little apology to offer up.  Or, do you do what I suggested to you:  Assume for the sake of argument that I am right and for your own benefit start working and researching so that you come to a complete understanding on your own?   Which of the two scenarios do you think will ultimately be better for you?

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #55 on: May 09, 2016, 02:21:33 PM »
No such voltage or inductor exist--not even close.

The fact is MH,and this is an absolute fact,you cannot back up your answer with a real world test to show you are correct.
There is no such thing as an ideal inductor,nor is there any such thing as an ideal voltage.

An ideal inductor has no resistance,and inductance it self produces resistance-a resistance to the change in current. So an ideal inductor dose not exist for that very reason,and there for your question cannot be answered-well maybe in MH fairy land.

An ideal voltage also dose not exist. There is no device that can provide an infinite amount of current to maintain an ideal voltage across a dead short that is also ideal-being a short that will never collapse under any load.

Brad

A real inductor can be 99.99% identical to an ideal inductor.  Ideal voltage sources exist right now within certain limitations.  A good bench power supply is an ideal voltage source.  A car audio amplifier is an ideal voltage source that can output The Star Spangled Banner as an ideal voltage.  I explain that all on the other thread.

The real-world test can easily be done as explained on the other thread.  The only limitation is that the real-world inductor will behave a tiny smidgen differently from the ideal inductor.

You are just making phony dismissive arguments that take you off track.  The point of the exercise is perfectly clear:  To understand how an inductor works.

#### tinman

• Hero Member
• Posts: 5242
##### Re: MH's ideal coil and voltage question
« Reply #56 on: May 09, 2016, 02:26:12 PM »
The way you have to "see it" is to use your intellect to understand how an inductor works.

The only question is what do you do?  Do you stick it out and refuse to explore other options until at the end you are spoon fed the answer?  If you agree the answer is correct then you will have a rather embarrassing little apology to offer up.  Or, do you do what I suggested to you:  Assume for the sake of argument that I am right and for your own benefit start working and researching so that you come to a complete understanding on your own?   Which of the two scenarios do you think will ultimately be better for you?

Quote
The sim will work perfectly and I am glad that you don't want to see it.

I think you will find that it will not,well at least it did not on the thread i read on OUR.
Poynt had to add a resistance in series with the ideal inductor,and as your question dose not include a resistance,then the sim must represent your ideal inductor that has no resistance.

Quote
You are clearly still stuck like glue to your mistake.

As you ,nor anyone else has proven that i have made a mistake,then my answer stands-you cannot connect an ideal voltage across an ideal inductor.

Brad

#### partzman

• Sr. Member
• Posts: 363
##### Re: MH's ideal coil and voltage question
« Reply #57 on: May 09, 2016, 02:37:34 PM »
Considering a sim to provide an answer here is a good thing because all simulators I've used will not allow an inductor with zero resistance. Some low value will be assigned if the operator fails to fill in the blank.  So, what we have to consider is what happens as the resistance approaches zero.

For example, what will the current be at T=0 when we apply the assumed ideal voltage source of 4 volts to the 5 henry inductance with a dc resistance of 1 ohm? Will it be 4 amps?  How about .01 ohm, will it be 400 amps or?  How about 1e-10 ohms, will it be 4e10 amps?

Looking at the problem from another angle, if we assume we had somehow achieved a current level of 2.4 amps in our ideal inductor with zero resistance and we then shorted it with a perfect conductor having zero resistance, what happens to the inductor current?

partzman

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #58 on: May 09, 2016, 02:40:12 PM »
Somebody has already posted on this thread very recently how an ideal inductor behaves.  I am sure that you can sense that Poynt is in agreement with me.

The best course of action for you would be to understand what inductance really is an how it behaves.  You are arguing that there is a radical discontinuity between how an ideal inductor behaves and a real-word inductor with a 0.0000000001 ohm wire resistance behaves.  Nature does not like discontinuities at all.  Just that fact should get you thinking again and hopefully find you going in the right direction.

"Nature does not like discontinuities at all."

#### MileHigh

• Hero Member
• Posts: 7600
##### Re: MH's ideal coil and voltage question
« Reply #59 on: May 09, 2016, 02:44:07 PM »
I am really surprised that a sim program would balk at an ideal inductor but if that's the case there must be a circuit condition where there is a problem.  However, in my my example I can't see the sim encountering a problem like a divide-by-zero error or whatever.