MH's ideal coil and voltage question

[tinman]

You may wish to exercise a few examples to see if your conclusion is correct. Your conclusion being that if the time constant (Tau) is infinite, the load immediately presents itself as a perfect short, meaning the current will be infinite and instantaneous.

Here are a few: (in all cases, L=6H)

1) R=1, Tau=6s
2) R=0.1, Tau=60s (1min)
3) R=1m Ohm, Tau=60ks (16.6 hours)
4) R=1u Ohm, Tau=6M(million)s (1667 hours)
5) etc.

What is happening to Tau as R decreases?
If R could be 0, Tau must be infinite.

What happens to the inductor current after t=0 when Tau=infinity?

This is the very reason that MHs question cannot be answered,as i have stated before.
The conundrum kicks in at T=0.
If R = 0,which id dose,as the inductor is ideal,then no current flows through the ideal inductor.
If Tau is infinite,then 10% of maximum current flow is also an infinite amount of time,and so is 1% of maximum current flow,and so is .1% of maximum current flow-ETC. This means that it will also take an infinite amount of time before current start to flow,as there is no division of infinite that it self is not infinite. This means that there is no inductance,as there is no current flow to create a magnetic field,and there for no CEMF to resist the change in current that isnt flowing anyway

But there is also no resistance in an ideal coil,and so the ideal voltage is now across a dead short.
So now we have an infinite amount of current flow

MH quoted him self--Quote:  there is no time constant--post 14

So,the current either rises instantly,or the current rise time is infinite,which means there is no current flowing through the ideal coil.


Brad

[tinman]

L/0=infinite

As i thought


Brad

[tinman]

A sim of an ideal V source across an ideal inductor will crash the sim.

A tiny bit of resistance must be added as the computational resolution is finite.

So this means we cannot sim MHs question as it is defined ?

Brad

[MileHigh]

<<< So,the current either rises instantly,or the current rise time is infinite,which means there is no current flowing through the ideal coil.  >>>

Sorry but I have to lol, when the "answer" is two completely contradictory answers.

[tinman]

 author=MileHigh link=topic=16589.msg483543#msg483543 date=1462799110]



That is what you need to focus on.

MileHigh
[/quote]

You are just getting belligerent for no reason and you are twisting your logic and not really making sense.

No i am not MH. I am working on your question using the values and components you described.

I said that a real-world coil can be 99.99% identical in behaviour to an ideal coil.  That means the difference in their behaviour on the bench will be one part in 10,000.  That's pretty damn similar.

I think you will find that there is a huge difference between an ideal inductor,and a real world inductor MH. And once this is resolved,then you will find that your near enough to ideal power supply is not even close to being ideal.

The point being again that discussing ideal coils or ideal voltage sources is not far fetched at all.

If we are going to be accurate and true to our selves in this discussion,then i think you are going to find that there is an infinite gap between real and ideal.

This is the real topic of discussion:  a) What is inductance?  b) Demonstrate your understanding of inductance by solving for the current for an ideal inductor in a simple circuit.

Your simple circuit requires resistance,and is normally a resistor added in series with an ideal inductor. But your question and comments that follow say there is no resistance,and so, it cannot be resolved,as poynt has just stated in regards to the sim test.


Brad