Joule Thief 101

[Magneticitist]

But, do we agree that a coil with 0 resistance does not/can not exist?  I hope that we do, otherwise, I am missing something major.

IF I am correct about this, then what good does "knowing" how a coil with 0 resistance will act do for us?

I am not arguing anything as this is not my field and I am here to learn.

Bill

out of fairness one could say that he IS trying to argue that, but only in his exercise.
in his exercise he is trying to establish that a 0 resistance is for all intents and purposes the same
as .0000001 resistance, so in his exercise, current would indeed flow as proven by the flow shown in the inductors with extra low resistance. however he asked it in a question you could say some of us are simply overthinking because we feel the need to establish 0 resistance is an impossibility because it is a word we give to a key factor in circuit theory and how we calculate many other factors we have names for.  so basically MH wanted to show that Brad didn't have the EE knowledge to do the math on the exercise and Brad is trying to show once again that MH's answer cannot be right due to the simple fact that R=0. even if Brad answered the questions assuming in this exercise R=0 indeed behaves like R=.0000001 in a window of time, I personally don't see the point of it. Brad could then pop quiz MH on how his Joule Thief worked and it would be the same argument all over again.

[tinman]

But, do we agree that a coil with 0 resistance does not/can not exist?  I hope that we do, otherwise, I am missing something major.

IF I am correct about this, then what good does "knowing" how a coil with 0 resistance will act do for us?

I am not arguing anything as this is not my field and I am here to learn.

Bill

If an ideal inductor existed,one having no resistance,no capacitance,and did not dissipate any power,then no current would flow through it,as the CEMF would also be ideal,and equal to that of the EMF. Both would produce the same amount of current,but which flow in opposite directions--and so the net result is 0 current flow.

This is the behaviour of an ideal inductor--everything is !ideal!.


Brad

[MileHigh]

But, do we agree that a coil with 0 resistance does not/can not exist?  I hope that we do, otherwise, I am missing something major.

IF I am correct about this, then what good does "knowing" how a coil with 0 resistance will act do for us?

I am not arguing anything as this is not my field and I am here to learn.

Bill

How can you possibly understand how a real-world coil will behave if you don't also know how an ideal coil behaves?  A real-world coil is the synthesis of an ideal coil and a resistance.  Deriving how a real-world coil works and generating the formula comes directly from fully understanding how an ideal coil works, and how a resistance works.  Makes sense?

What good comes from knowing this?  What good comes from knowing how an aircraft wing gives you lift?  Honestly, it's a ridiculous question.

Let's take an example of an ICE.  Say we have a 300 HP 8-cylinder engine.  I am just going to guess some numbers now.  We know from measurements let's say at idle in a real car it burns off 2 HP of gas.  Let's say that we also know that the HP drain from the main bearings in the engine is 1/2 HP.

Now, can we imagine replacing the bearings with "magic" perfectly frictionless bearings?  We can do that pretty darn easily.  If the engine had perfectly frictionless bearings would it still pretty much run the same way?  For sure it would, except now when it is at idle, it will burn 1 1/2 HP of gas instead of 2 HP of gas.

Now, is this frictionless-bearing ICE that hard to imagine in your engine designer's brain?  The answer is no, the ICE will perform almost identically.  Who does not have the capacity to imagine that?  Not many people at all.

It's the same thing with a 5 Henry ideal coil and a 5 Henry coil with a wire resistance of 0.001 ohms.  It is no stretch of the imagination at all to imagine how the ideal coil will behave if you assume that you know how the real 5 Henry coil will behave.  The whole thing is a tempest in a teapot, a waste of time.

[MileHigh]

If an ideal inductor existed,one having no resistance,no capacitance,and did not dissipate any power,then no current would flow through it,as the CEMF would also be ideal,and equal to that of the EMF. Both would produce the same amount of current,but which flow in opposite directions--and so the net result is 0 current flow.

This is the behaviour of an ideal inductor--everything is !ideal!.

Brad

It's time to get real Brad.  The real coil and the ideal coil both produce equal CEMF to counter the EMF applied by the voltage source.

How does either type of coil respond to the EMF?  Continuously increasing current flows through the coil as long as the EMF is applied.  The CEMF is a direct result of increasing current flowing through the coil.  That's how a bloody inductor works!

Get yourself out of this quagmire and move forward and try to answer the question.

[Pirate88179]

What good comes from knowing this?  What good comes from knowing how an aircraft wing gives you lift?  Honestly, it's a ridiculous question.

Well, thanks for the response but, I do not think it was a ridiculous question.  Your wing analogy is a poor one as you are talking apples and oranges here.  The more accurate comparison would have been knowing how an "ideal" aircraft wing works (One with 0 drag) which also does not exist.  So, to me, knowing how an ideal (non-existent) aircraft wing performs is useless if I already know how a real life aircraft wing works.  You see?  Why get involved with 0 drag and infinity lift when studying airfoil designs when neither is possible? (If you have L/D and D=0 then we are diving by 0 again and..well...you know...)

Also, in the wing example, you can not say that an ideal wing (airfoil design) will perform almost identically to a real wing design like you are saying with your coil.  Same with the ICE analogy.

To me, it is useless and a total waste of time considering how an "ideal" anything, (which does not/can not exist) performs under imaginary conditions.

We can agree to disagree on this point but, I have been involved in many, many engineering design projects over the years and never, ever...even once, did we model something that did not, or could not exist to determine our final design.

Bill

PS  Maybe the guys that designed the components for my computer did as you are saying, maybe the folks that built the hard drives and servers for the net did so also...if so, I take my hat off to them.  I just can not picture them wasting valuable time
considering impossible design parameters.