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Author Topic: MH's ideal coil and voltage question  (Read 477918 times)

Magluvin

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Re: MH's ideal coil and voltage question
« Reply #390 on: May 14, 2016, 06:39:59 PM »
I kind of like it because it stimulates us to think.
I think this discussion is beneficial to all involved as long as Ad Hominem remarks are absent.
The confusion will disappear immediately when you consider the coupling coefficient (k) between these two "separate coils" connected "in parallel".

In an ideal toroid the flux is completly shared and k=-1, thus in fact these coils are connected in anti-parallel when flux direction is considered. Thus they do not posses any inductance collectively. Consequently their anti-parallel combination possesses zero reactance and zero resistance, leading to zero impedance and the current flowing through the voltage source rises immediately to infinity.
It is pretty useless from an engineering standpoint, but it has a great educational value.
Anyway, it is what Tinman was referring to all along while you were apparently analyzing Fig.2.


Great thinking. ;)   It is the reverse of the ideal inductor idea of no current can flow, where in your point here is there is no reactance, and the single inductor has 100% reactance.   ;) In an ideal world.

Mags

partzman

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Re: MH's ideal coil and voltage question
« Reply #391 on: May 14, 2016, 06:50:22 PM »
Attached is an equivalent circuit of MH's question using ideal components.  The questions are, can we vary Vg and can we use delta I = E*t/L to analyze this circuit? If not, why? The main objection has been the short circuited this and that. I don't see any short circuits.  What an I missing here?

partzman


MileHigh

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Re: MH's ideal coil and voltage question
« Reply #392 on: May 14, 2016, 06:54:18 PM »
But we will never know,as he never would answer his own question ::)


And isn't it a good thing that I refused to answer the easy question and only answered the hard question, because slowly but surely you are actually learning something now.

poynt99

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Re: MH's ideal coil and voltage question
« Reply #393 on: May 14, 2016, 06:59:38 PM »
But we agree that the inductor is now a shorted loop,and current is flowing through this circuit loop that includes the ideal voltage source(not to be confused with the ideal voltage,which now has a value of 0 volts)

To quote verpies
So now i ask--
At 0 volts we both agree that we are in a shorted(looped) condition,and a steady current is flowing through this shorted ideal inductor loop,and due to the 0 resistance value,it will continue to flow infinitely.
As I said, I am not arguing against that.

Quote
How is this short removed just by turning up the voltage on the ideal voltage source?
If it is not removed,then how are you placing a voltage across this !now shorted! ideal inductor?
The short is not removed. The voltage source itself is the short (if you will), but it doesn't short itself out!

Quote
The paradox being-quote verpies-->It is impossible to connect such voltage source across a shorted ideal inductor.
There is no paradox, and verpies is wrong because the inductor does not represent a short the moment it is connected to something, even an ideal voltage source. The only true paradox I've seen so far is verpies' application of an ideal voltage source across an ideal short. Which one wins? That is your paradox Brad.

As I said, talk of such abstract theories as being posed is not helping the understanding here in any way, it is only hindering it.

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #394 on: May 14, 2016, 07:17:12 PM »
As I said, talk of such abstract theories as being posed is not helping the understanding here in any way, it is only hindering it.

I agree, Verpies is too far out sometimes.  His comments on the thread from a couple of days ago were barely comprehensible.

Verpies:  I suggest that you step it down a notch and add some more description at times so your message is more readily understood by both the "ordinaries" and the "gurus."

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #395 on: May 14, 2016, 07:19:39 PM »
Attached is an equivalent circuit of MH's question using ideal components.  The questions are, can we vary Vg and can we use delta I = E*t/L to analyze this circuit? If not, why? The main objection has been the short circuited this and that. I don't see any short circuits.  What an I missing here?

partzman

You are absolutely 100% dead on.  Will the train see the light at the end of the tunnel and actually emerge from the tunnel in one piece?  That is the question of the hour.

Magluvin

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Re: MH's ideal coil and voltage question
« Reply #396 on: May 14, 2016, 08:08:26 PM »
As I said, I am not arguing against that.
The short is not removed. The voltage source itself is the short (if you will), but it doesn't short itself out!
There is no paradox, and verpies is wrong because the inductor does not represent a short the moment it is connected to something, even an ideal voltage source. The only true paradox I've seen so far is verpies' application of an ideal voltage source across an ideal short. Which one wins? That is your paradox Brad.

As I said, talk of such abstract theories as being posed is not helping the understanding here in any way, it is only hindering it.


I agree with you on the no current flow at t/0 of an ideal inductor. 

But I dont think that if we're to study the ideals if an ideal inductor that we should ignore the mechanism that makes it do what it does. If resistance is zero, and no losses, then that underlying ideal inductor mechanism should be lossless and 100% efficient also. And if that mechanism is lossless then the the inductor should continuously impede an emf presented at the input. ;)   PW says that a straight wire has inductance, and I agree, no matter how tiny the inductance is. So it may be that the ideal straight wire may not be able to pass current if the inductance mechanism is 100% efficient. Does that make any sense at all? If not then where might we find reference that tells us otherwise so we can examine that if possible?

In the real world we have resistance mostly no matter what. So all those losses, voltage drops no matter how tiny would definitely affect the efficiency of that mechanism to be less than 100% efficient, thus there could not be a 100% impediment to the input and the inductor would now work as we know them.

Mags


Magluvin

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Re: MH's ideal coil and voltage question
« Reply #397 on: May 14, 2016, 08:32:59 PM »

I agree with you on the no current flow at t/0 of an ideal inductor. 

But I dont think that if we're to study the ideals if an ideal inductor that we should ignore the mechanism that makes it do what it does. If resistance is zero, and no losses, then that underlying ideal inductor mechanism should be lossless and 100% efficient also. And if that mechanism is lossless then the the inductor should continuously impede an emf presented at the input. ;)   PW says that a straight wire has inductance, and I agree, no matter how tiny the inductance is. So it may be that the ideal straight wire may not be able to pass current if the inductance mechanism is 100% efficient. Does that make any sense at all? If not then where might we find reference that tells us otherwise so we can examine that if possible?

In the real world we have resistance mostly no mater what. So all those losses, voltage drops no matter how tiny would definitely affect the efficiency of that mechanism to be less than 100% efficient, thus there could not be a 100% impediment to the input and the inductor would now work as we know them.

Mags

See, something MH said bothered me a bit. He said that a resistance of .000001ohm,  1uohm was virtually seemless to being an ideal inductor. Would you agree with that statement? Not trying to pit you against him. But it would be nice if that statement were to be considered true by you or not and give us your understanding as to why your answer is what it is. 

I say it is very far from seamless, pretend world or not.   It was said by Carl Segan that if we cut an apple pie in half, then cut 1 half in half, then cut 1/4 in half, and keep going, I think the number was about 70 or 90 cuts to get to a single atom.  It was less than 100 cuts. But we could go further and further, somehow. When does it end?   So the '1uohm is seamless with an ideal component' is not an accurate statement and we cannot accept that as fact here. .5uohm  has half the resistance of his idealized 1uohm. What about .001uohm? .001 pico ohm?  .000000001pico ohm?    So I think that should be resolved on that seamless bit. It is not a good representation, of which happens quite often.


Mags

Magluvin

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Re: MH's ideal coil and voltage question
« Reply #398 on: May 14, 2016, 08:49:50 PM »
See, something MH said bothered me a bit. He said that a resistance of .000001ohm,  1uohm was virtually seemless to being an ideal inductor. Would you agree with that statement? Not trying to pit you against him. But it would be nice if that statement were to be considered true by you or not and give us your understanding as to why your answer is what it is. 

I say it is very far from seamless, pretend world or not.   It was said by Carl Segan that if we cut an apple pie in half, then cut 1 half in half, then cut 1/4 in half, and keep going, I think the number was about 70 or 90 cuts to get to a single atom.  It was less than 100 cuts. But we could go further and further, somehow. When does it end?   So the '1uohm is seamless with an ideal component' is not an accurate statement and we cannot accept that as fact here. .5uohm  has half the resistance of his idealized 1uohm. What about .001uohm? .001 pico ohm?  .000000001pico ohm?    So I think that should be resolved on that seamless bit. It is not a good representation, of which happens quite often.


Mags


Cut that 1uohm in half, 90 times.  Are we done yet? Are we on the verge of an ideal component with zero losses yet?

Mags

partzman

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Re: MH's ideal coil and voltage question
« Reply #399 on: May 14, 2016, 09:59:43 PM »

I agree with you on the no current flow at t/0 of an ideal inductor. 

But I dont think that if we're to study the ideals if an ideal inductor that we should ignore the mechanism that makes it do what it does. If resistance is zero, and no losses, then that underlying ideal inductor mechanism should be lossless and 100% efficient also. And if that mechanism is lossless then the the inductor should continuously impede an emf presented at the input. ;)   PW says that a straight wire has inductance, and I agree, no matter how tiny the inductance is. So it may be that the ideal straight wire may not be able to pass current if the inductance mechanism is 100% efficient. Does that make any sense at all? If not then where might we find reference that tells us otherwise so we can examine that if possible?

In the real world we have resistance mostly no matter what. So all those losses, voltage drops no matter how tiny would definitely affect the efficiency of that mechanism to be less than 100% efficient, thus there could not be a 100% impediment to the input and the inductor would now work as we know them.

Mags

Mags,

I am not the one you asked for an answer on this but I will go ahead and offer my opinion.  It appears from your comment highlighted above, you assume that if an inductance is 100% efficient, it will not allow any current to flow. At 100% efficiency, the emf is totally cancelled by the cemf thus resulting in zero current flow or infinite inductance.  It must have even the smallest amount of resistance to perform like a real inductor.

When we apply the formula delta I = E*t/L or rearrange the formula to solve for inductance of emf, we assume ideal conditions such as an ideal inductance.  The answer we get from using this formula on an inductance with resistance is very close to what we would measure on the bench. The less dc resistance the coil has, the closer the answer is. From this we can deduce that an ideal 5h inductance is just that, 5h with no impediment from any resistance.

partzman

 

Magluvin

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Re: MH's ideal coil and voltage question
« Reply #400 on: May 14, 2016, 10:38:23 PM »
Mags,

I am not the one you asked for an answer on this but I will go ahead and offer my opinion.  It appears from your comment highlighted above, you assume that if an inductance is 100% efficient, it will not allow any current to flow. At 100% efficiency, the emf is totally cancelled by the cemf thus resulting in zero current flow or infinite inductance.  It must have even the smallest amount of resistance to perform like a real inductor.

When we apply the formula delta I = E*t/L or rearrange the formula to solve for inductance of emf, we assume ideal conditions such as an ideal inductance.  The answer we get from using this formula on an inductance with resistance is very close to what we would measure on the bench. The less dc resistance the coil has, the closer the answer is. From this we can deduce that an ideal 5h inductance is just that, 5h with no impediment from any resistance.

partzman

Yes you do understand my point. Thanks.

As for the rest of it, how can we deduce that the CEMF that counters the input isnt equal to the input?  Maybe there is something a miss here. Why isnt the cemf ideal also when it comes to the ideal inductor? Where is the calculation of some loss that keeps the cemf lower than the input? 

Again, the sim says what the sim says. Look at the graph again and expand that time out for hours or even days. There will always be a curve in the real world no matter the level of resistance. Who is to say that with absolute zero resistance that the mechanism that is at work in the inductor that impedes the input still has some sort of loss in order for it to be that the cemf is not equaled to the input applied, all of the time? How does that formula account for that? This is the question. ;) Maybe that possibility is ignored some how?  Like how would we know for sure without actual hands on testing of such a device? Yet we talk about it as if it is just standard thinking without going any deeper.  Just think a little deeper. How deep can we see beyond just some formula dropped on us and think thats all we need to know?

Mags
 

MileHigh

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Re: MH's ideal coil and voltage question
« Reply #401 on: May 14, 2016, 11:00:31 PM »
You are dealing with the same problems in understanding, and the same "rules" that are seemingly made up on the fly using incorrect logic, and the same lack of understanding in how an inductor actually works.

When you connect a real or ideal voltage source to a real or an ideal inductor, or to a resistor, then the EMF imposed on any of those three devices results in a CEMF in the device that is always equal and opposite to the EMF.

The idea that the CEMF must be a bit lower than the EMF for current to flow is 100% wrong, it's a "rule" that has been made up because it "sounds right."

The resistor responds to the EMF with a resultant current flow and that power is burnt off as heat.

The real or ideal inductor responds to the EMF with a resultant current flow and that power is stored in the magnetic field and if there is a resistance then a small amount of that power is burned off as heat.

Why does the inductor do what it does?   Why does the shopping cart move when you push on it?  Read about an inductor and understand its dynamic response to changing voltage conditions.  This is a device whose response is determined by differential and integral equations.  Learn intuitively how an inductor responds and learn and understand the equations that back up the intuitive understanding of how the inductor responds.  A shopping cart's response is intuitive, you have to get to the point where the inductor's response is intuitive.

I will repeat that this notion that "if the CEMF is the same as the EMF then current will not flow" is a fallacy.  It does not apply to a resistor, and it does not apply to an inductor.

What about a capacitor?  If the CEMF from the capacitor is the same as the EMF applied to it, does any current flow?  The answer is no, there is no current flow.  The capacitor is simply not the same as the resistor or the inductor.  That's just the way it is and if you want to understand electronics then you have to understand these things.

What about "ideal CEMF?"

You guys define "ideal CEMF" first, and then perhaps we can discuss it.  What does that actually mean?  Or is that just a meaningless term that has been made up on the fly?  Lay your cards on the table about this "ideal CEMF" business.
« Last Edit: May 15, 2016, 02:28:28 AM by MileHigh »

partzman

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Re: MH's ideal coil and voltage question
« Reply #402 on: May 14, 2016, 11:36:56 PM »

Who is to say that with absolute zero resistance that the mechanism that is at work in the inductor that impedes the input still has some sort of loss in order for it to be that the cemf is not equaled to the input applied, all of the time? How does that formula account for that? This is the question. ;)

Mags

That's a fair enough question. Let's see if we can logically work out an answer. Obviously the formula(s) don't seem to supply a suitable answer because they assume ideal components. So, maybe we can look at one factor that determines the inductance L of a real air coil for example.  This would be the geometry of the coil such as turns, spacing, length of winding and diameter of windings.  Apart from any outside influence, this geometry would determine the effect of the self induced emf or cemf produced by the time rate change of current or dI/dt on the applied emf which is basically the inductance of the coil.  If we now reduce the resistance of the coil windings to zero, we still maintain the same geometry.  So are we to say that the laws of induction due to this particular geometry are going to change because of zero resistance? Or will this example coil become an ideal inductor with pure inductance as determined by it's geometry?

Regarding simulation of an ideal inductor, our current limited versions only offer us the ability to compare a reasonable resistance to a very small resistance.  I was able to get LtSpice to simulate the 5H inductor with a dcr of 1e-320 without blowing up.  The point of this is, the current slope is straighter or has less droop over time with every decrease in dcr. So, could we assume that a trend is established that says if we continue to decrease the dcr to zero, we will experience an infinite straight current line with a perfect dI/dt representing the ideal inductance?

partzman

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poynt99

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Re: MH's ideal coil and voltage question
« Reply #403 on: May 15, 2016, 12:50:24 AM »
MH, ;)

Magluvin

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Re: MH's ideal coil and voltage question
« Reply #404 on: May 15, 2016, 12:54:33 AM »
Working on my bike. The quick release lever shaft broke and the nut to nut fasteners on one end of the axle came loose and tightened the axle solid. Couldnt even push it back as the threads of the axle were digging into the axle holder slots. Was on my way back from the beach to get a little sun and see the beautiful women in bikinis everywhere. Then tragedy. About 3 miles from my shop or home. Some guys in a truck offered me a ride.  ;D   So now I am in fix the bike mode.

The bike is electric. About 80lb. So walking it back was a hard option without the wheel working in any way that it should.

I looked over what both of you posted. Ill go over it again after.  Thanks for the explanations. That is all Ive been asking for. Lets see if it all fits.

Back later.

Mags