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Author Topic: MH's ideal coil and voltage question  (Read 477575 times)

tinman

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Re: MH's ideal coil and voltage question
« Reply #195 on: May 11, 2016, 01:07:00 AM »
Brad,

To be clear, I am in agreement with MH. It makes sense to me now, and apparently when I answered the question years back on OUR, I also got the answer correct.

Regarding my simulation, when using such small resistance values without changing some settings in SPICE (LT Spice must already be set to handle this), the simulation engine runs out of computational precision, which is why it "flatlines" with very low values. When the value is too low, the sim runs out of gas and starts making gross approximations, which is evident below with R=1f Ohm. But you do see that it is honing in on the 2.4A value? Any smaller in value and the trace just flatlines.

For an ideal inductor, yes Tau is infinite, but this has does not preclude current flow through the inductor. If however the inductance was an unrealistically large value like 1 million Henries, then yes the current would essentially be zero for a relatively long duration of time. That was my confusion. Tau simply determines the rise time, and since it is infinitely long, the trace becomes a nice straight line rather than the curve we normally see.

I was wrong in my analysis, but it is clear to me now.

I dont think it is clear Poynt,and your original thought (current will not flow)is correct.

If your sim can replicate any real electrical event in a circuit,why dose it crash when you use an ideal inductor that no resistance?. Why is your sim unable to carry out a simple analysis such as you think MH has successfully done?.

The answer is simple,and as i stated. MH is using math that is based on the premise that the inductor will reach a maximum current level. !!Can you calculate what the maximum current level will be of an ideal inductor using MHs calculations? Will this answer (When t = 3 seconds that's 12/5 = 2.4 amps) then be correct?.

When modeling a circuit ,an ideal inductor is used--along with a series resistor that mimics the resistance that would exist in a real world inductor. This is why you have to place some resistance in series with your ideal inductor in your sim to stop it crashing.

Why dose your sim crash without it?
Because your using an ideal inductor. An ideal inductor has ideal inductance,no resistance,no capacitance,and dose not dissipate power. This means that the CEMF is also ideal,and so is equal to the EMF ,and so an equal current will flow in the opposite direction to that of the current produced by the EMF.

Here is verpies statement.
Since an ideal inductor must have a zero resistance, this means that it must be shorted (if it ain't shorted, it ain't ideal) and it becomes physically impossible to connect any real voltage sources in series with it.Not only an ideal inductor is devoid of an asymptotic V/R current limit but also the current through an inductor of infinite inductance, that is somehow connected to an ideal voltage source, could never change because of the implied zero di/dt at any voltage.

Remember-it is only the resistance and parasitic capacitance that allows the EMF to be greater than the CEMF,and allow the flow of current,something that an ideal inductor is void of.


Brad

Magneticitist

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Re: MH's ideal coil and voltage question
« Reply #196 on: May 11, 2016, 01:12:41 AM »
An EMF measured across an open inductor is proportional to the rate of change of flux penetrating that inductor (dΦ/dt).
EMF measured across an inductor is not proportional to the current flowing through it and in an open inductor the current cannot flow at all.
Precursor of what?

well, look.. I hadn't thought about this kind of stuff in a while and in this debate tried to quickly brush up on my terminology online, and read how the EMF is actually the potential. I was thinking the electric field was the voltage when apparently that's not a metaphor. Now I don't really know what to call what at the moment because I am getting more confused at the terminology other people are using that seems to contradict what I just read. I need to spend some more time reading this in detail before I know exactly what do call what here but I think of it like electric- voltage, magnetic - current. maybe that is a complete falsehood that has emerged from too much misinterpreted tinkering and not enough reading. at any rate the point I was trying to make is that any magnetic force that is present is present when there is current flowing and if not we just have voltage from the source.
there's no di/dt to even consider, no magnetic field to consider, no lenz to consider, because it's all perfectly working against itself in theory and pretty much just not existing at all. like any inductor the voltage is the precursor unlike the opposite in a capacitor.

allcanadian

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Re: MH's ideal coil and voltage question
« Reply #197 on: May 11, 2016, 03:33:25 AM »
@Tinman
Quote
Remember-it is only the resistance and parasitic capacitance that allows the EMF to be greater than the CEMF,and allow the flow of current,something that an ideal inductor is void of.


I would agree and if the resistance is defined as zero in the question then Ohms law has no application... let's move on. No resistance and no capacitance which leaves an Electro-Motive Force from the source which are Coulomb forces due to the Ideal voltage source electric field. The source Emf acts forward however the moment something tries to move a magnetic field evolves producing an equal and opposite Counter-Force, our Cemf, which opposes the charges motion.


Logic suggest that if nothing can dissipate and energy is perfectly conserved then the Cemf must balance perfectly with the source Emf... remember these are perfectly conserved forces. If an ideal superconductor produces a perpetual loss-less current closed loop then an ideal superconducting coil must also produce a perpetual loss-less Cemf countering our source Emf. One cannot say the rules always apply then change the rules simply because they do not like the answer. Either the forces balance perfectly and energy is conserved or energy is not conserved in a loss-less system and we have problems. Ideally it must be ideal because we have already defined it as such.


AC

tinman

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Re: MH's ideal coil and voltage question
« Reply #198 on: May 11, 2016, 06:35:28 AM »
@Tinman

I would agree and if the resistance is defined as zero in the question then Ohms law has no application... let's move on. No resistance and no capacitance which leaves an Electro-Motive Force from the source which are Coulomb forces due to the Ideal voltage source electric field. The source Emf acts forward however the moment something tries to move a magnetic field evolves producing an equal and opposite Counter-Force, our Cemf, which opposes the charges motion.


Logic suggest that if nothing can dissipate and energy is perfectly conserved then the Cemf must balance perfectly with the source Emf... remember these are perfectly conserved forces. If an ideal superconductor produces a perpetual loss-less current closed loop then an ideal superconducting coil must also produce a perpetual loss-less Cemf countering our source Emf. One cannot say the rules always apply then change the rules simply because they do not like the answer. Either the forces balance perfectly and energy is conserved or energy is not conserved in a loss-less system and we have problems. Ideally it must be ideal because we have already defined it as such.


AC
Absolutely  AC
Ideal means perfect-a losless conversion between EMF-forward current-counterEMF-reverse current.of the same amount.

So that would mean a dead short when an ideal voltage from an ideal source is placed across the ideal inductor,as as much current would be trying to flow back into the ideal voltage source,as the ideal voltage source is trying to deliver.

My answer stands--you cannot place an ideal voltage across an ideal inductor.

Brad

Magneticitist

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Re: MH's ideal coil and voltage question
« Reply #199 on: May 11, 2016, 07:32:20 AM »
@Tinman

I would agree and if the resistance is defined as zero in the question then Ohms law has no application... let's move on. No resistance and no capacitance which leaves an Electro-Motive Force from the source which are Coulomb forces due to the Ideal voltage source electric field. The source Emf acts forward however the moment something tries to move a magnetic field evolves producing an equal and opposite Counter-Force, our Cemf, which opposes the charges motion.


Logic suggest that if nothing can dissipate and energy is perfectly conserved then the Cemf must balance perfectly with the source Emf... remember these are perfectly conserved forces. If an ideal superconductor produces a perpetual loss-less current closed loop then an ideal superconducting coil must also produce a perpetual loss-less Cemf countering our source Emf. One cannot say the rules always apply then change the rules simply because they do not like the answer. Either the forces balance perfectly and energy is conserved or energy is not conserved in a loss-less system and we have problems. Ideally it must be ideal because we have already defined it as such.


AC

I don't see why we should have to take it further than "perfectly and absolutely resists current change".  This automatically means no EMF or counter EMF doesn't it?

picowatt

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Re: MH's ideal coil and voltage question
« Reply #200 on: May 11, 2016, 07:33:21 AM »
Absolutely  AC
Ideal means perfect-a losless conversion between EMF-forward current-counterEMF-reverse current.of the same amount.

This would more so describe an ideal inductor that also has an infinite amount of inductance.  As such, when connected across a voltage source, no current would ever flow as the time constant would also be infinite.  An ideal inductor with infinite inductance would appear to be a continuous open circuit when connected in parallel with a voltage source.

Consider the superconducting magnet used in an MRI machine.  Typically, they have a total inductance of around 6000Hy.  They are "charged" very slowly to a couple hundred amps or so with an adjustable current limited source to prevent an excessive overvoltage condition.

Quote

So that would mean a dead short when an ideal voltage from an ideal source is placed across the ideal inductor,as as much current would be trying to flow back into the ideal voltage source,as the ideal voltage source is trying to deliver.

My answer stands--you cannot place an ideal voltage across an ideal inductor.

You seem to be describing an ideal capacitor with an infinite amount of capacitance.  An ideal capacitor with an infinite amount of capacitance would have an infinite time constant and appear to be a continuous short circuit when connected in parallel with a voltage source.

That's my 2 cents for now.  I've been away and will try to catch up on this thread as time allows.  Very busy...

PW

Magneticitist

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Re: MH's ideal coil and voltage question
« Reply #201 on: May 11, 2016, 07:44:31 AM »
This would more so describe an ideal inductor that also has an infinite amount of inductance.  As such, when connected across a voltage source, no current would ever flow as the time constant would also be infinite.  An ideal inductor with infinite inductance would appear to be a continuous open circuit when connected to a voltage source.

Consider the superconducting magnet used in an MRI machine.  Typically, they have a total inductance of around 6000Hy.  They are "charged" very slowly to a couple hundred amps or so with an adjustable current limited source to prevent an excessive overvoltage condition.

You seem to be describing an ideal capacitor with an infinite amount of capacitance.  An ideal capacitor with an infinite amount of capacitance would have an infinite time constant and appear to be a continuous short circuit when a voltage is applied across it.

That's my 2 cents for now.  I've been away and will try to catch up on this thread as time allows.  Very busy...

PW

let's say this is true, and it honestly makes a degree of sense even though I disagree in principle..
Wouldn't this mean the inductor is 'perfectly' accomplishing the exact opposite of what it's supposed to be perfectly doing in nature? Wouldn't the EMF and *CEMF be increasing against each other the entire time to infinity? And wouldn't that have to mean a continuously rising current?

How does that not constitute current change?
« Last Edit: May 11, 2016, 05:30:46 PM by Magneticitist »

minnie

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Re: MH's ideal coil and voltage question
« Reply #202 on: May 11, 2016, 10:53:25 AM »



  This photo is for the Tinman.
   Basically we get too much overunity and have to hand-rear the triplets.
   These are a few of this years pets.
   How about this for a business idea Tinman? Start the manufacture of
   braking systems for overunity machines.
    The one thing Wayne Travis got right on his early plans for his church
   was the provision of a cooling system!!!

tinman

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Re: MH's ideal coil and voltage question
« Reply #203 on: May 11, 2016, 11:37:27 AM »
I don't see why we should have to take it further than "perfectly and absolutely resists current change".

Quote
This automatically means no EMF or counter EMF doesn't it?

 What it means ,is that there can be no voltage across the ideal inductor--so yes.
It also means,as i said before,the current would be instant,and infinite--but no current flow. It would be much like supplying each end of a water pipe with water at 40psi. You would have pressure,but no flow.

Brad


tinman

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Re: MH's ideal coil and voltage question
« Reply #204 on: May 11, 2016, 12:06:16 PM »


Consider the superconducting magnet used in an MRI machine.  Typically, they have a total inductance of around 6000Hy.  They are "charged" very slowly to a couple hundred amps or so with an adjustable current limited source to prevent an excessive overvoltage condition.

You seem to be describing an ideal capacitor with an infinite amount of capacitance.  An ideal capacitor with an infinite amount of capacitance would have an infinite time constant and appear to be a continuous short circuit when connected in parallel with a voltage source.

That's my 2 cents for now.  I've been away and will try to catch up on this thread as time allows.  Very busy...

PW

Quote
This would more so describe an ideal inductor that also has an infinite amount of inductance.  As such, when connected across a voltage source, no current would ever flow as the time constant would also be infinite.  An ideal inductor with infinite inductance would appear to be a continuous open circuit when connected in parallel with a voltage source.

Thanks for joining PW.
I have to say that i dont agree with the ideal inductor needing to have an infinite inductance value.
Any iductor that is ideal is loss less -dose not dissipate power,due to having no resistance or capacitance. It converts or stores 100% of the energy it receives--ideal. Being the case,the current created when the v ideal voltage is placed across the ideal inductor,would create an CEMF and current of the same value--100% conversion--ideal.

Due to the fact that the voltage is also ideal,the source of that voltage must also be ideal.
Lets say it's an ideal battery,meaning that that battery could deliver 4 volts across any load without a voltage drop. The battery would also have to be ideal,and there for would have no internal resistance,and would not dissipate power by way of waste heat,or radiated energy of any type.

Once this ideal voltage source is hooked across the ideal inductor,as soon as any magnetic field started to form,it would produce an exact opposite,in the way of CEMF and current--ideal conversion. We know this to be true in an ideal situation,as everything has an equal and opposite reaction. In a non ideal situation,some of that equal and opposite is lost to heat due to resistance and parasitic capacitance--but not in an ideal situation,which is what the original question states the inductor and voltage source is--ideal.

The result would be an instant and infinite current build up between the ideal voltage source,and the ideal inductor,but no current would flow.And as there is no resistance throughout the circuit,no voltage would appear anywhere across that loop.

It is hard for some to understand what !ideal! mean's,but think about it long enough,and you begin to put all the pieces together.

Every action has an equal and opposite reaction--this dose not change.
And so,in this ideal situation,the CEMF must be equal and opposite to the EMF,and the current produced by the CEMF that apposes the current produced by the EMF must also be equal and opposite,as an ideal inductor dose not dissipate power.


Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #205 on: May 11, 2016, 12:09:31 PM »


  This photo is for the Tinman.
   Basically we get too much overunity and have to hand-rear the triplets.
   These are a few of this years pets.
   How about this for a business idea Tinman? Start the manufacture of
   braking systems for overunity machines.
    The one thing Wayne Travis got right on his early plans for his church
   was the provision of a cooling system!!!

Seems you have hit the bottle again John.

Any chance you could provide useful input into this thread?.


Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #206 on: May 11, 2016, 12:12:39 PM »
let's say this is true, and it honestly makes a degree of sense even though I disagree in principle..
Wouldn't this mean the inductor is 'perfectly' accomplishing the exact opposite of what it's supposed to be perfectly doing in nature? Wouldn't the EMF and CMF be increasing against each other the entire time to infinity? And wouldn't that have to mean a continuously rising current?

How does that not constitute current change?

Because the current produced by the inductor is equal and opposite to that being provided by the ideal voltage source,and so no current flows,but it dose rise to an infinite amount.



I have asked this question before--what happens when an unstoppable force meets an unmovable object?.


Brad

tinman

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Re: MH's ideal coil and voltage question
« Reply #207 on: May 11, 2016, 04:11:23 PM »
Well now I feel like I am in the Twilight Zone.

Poynt:  The current is one over "L" integral v dt.

That's 1/5 * integral (4) dt.

That's 1/5 * 4t.

That's 4/5*t.

When t = 3 seconds that's 12/5 = 2.4 amps.

Can we get out of the Zone now?

And when t= 20 seconds that's 9714.05 amps.
Poynt ran his sim for 100 second's (what would be the current then ?),and still he had no voltage drop :D


Brad

Pirate88179

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Re: MH's ideal coil and voltage question
« Reply #208 on: May 11, 2016, 04:46:18 PM »
Because the current produced by the inductor is equal and opposite to that being provided by the ideal voltage source,and so no current flows,but it dose rise to an infinite amount.



I have asked this question before--what happens when an unstoppable force meets an unmovable object?.


Brad


Like I said before...

The Big Bang.  Then, it all starts all over again.  An endless cycle.

Of course, this is just a theory.

Bill

minnie

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Re: MH's ideal coil and voltage question
« Reply #209 on: May 11, 2016, 05:17:18 PM »



     tinman,I've had a great find.
     Have a look at Electronics-Tutorials w.s.
     With all the crap you've been coming out with lately you're like me and
     really need to start from the very beginning.
     There's a lot about inductors and it's very basic and even I've been able
     to inch forward, albeit very slowly.
     Good luck,John.