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Author Topic: Magnetic Permeability ... I can't find anyone talking about this !!!!!  (Read 69607 times)

The Observer

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Hello,

Been Busy + my transmission just went out.

Anyways,  back EMF is darn interesting.

I am with Charlie that I would like to know exactly how this works and what is going on.
I need to know what the waves are doing.

I did find an experiment that could shed some light on this.

       http://www.physics.brown.edu/physics/demopages/demo/em/demo/5j1023.htm

The peak of the back emf is always greater than the applied voltage.
By the way, the very nature of this guy's experiment shows back emf can be harnessed.

Be Well,
             The Observer


fritz

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OK.

You have an ideal current source with 1mA. (at this point you should
now what an ideal current source is).
Then you connect a capacitor with capacity C in Farad.
What happens ?
The voltage rises
Well, if you reached 100Volts you disconnect.
Now you have W= 1/2 C*U^2 energy in the cap.
Fine, the voltage on the cap is still 100V.
What happens if you short-circuit the cap ?
You got a pretty(relatively) infinite current pulse in the opposite
direction. In practic you got propably 20 Amps current pulse in the
opposite direction.

OK.
Now we take a coil with inductivity L.
We connect the coil to an ideal voltage source with 10 Volts.
What happens ?
The current rises.
Well, now we short circuit the coil if it reached 1 Amps.
What happens ? - the current goes down slowly.
(on a superconducting coil - the current would stay at 1 Amp)
The energy in the coil at this point in time is W = 1/2 *L*I^2.
If you open now the current loop - you got a very high and
negative voltage - lets say 200V, depending on material.

What does this all mean ?

Capacitors and inductors can store energy.
The cap stores the energy if left open, the coil stores
the energy if shortened.
The capacitor can release this energy in a negative current pulse
with current multiple of the charging current. (theoretical infinite)
The inductor can release this energy in a negative voltage pulse
with voltage multiple of the charging voltage (theoretical infinite).

If it comes to DC and you have no superconducting coil - the coil
is a lousy energy storage (because of wire resistance) - but there
are MEMS - superconducting storage with powerplants on coil
basis - so its no theory.

Thats ___________very_______________ basic.

Better we avoid "Back EMF" because everbody means something
different.
In the posts before I meant the inner voltage of a dc motor caused
by the inerta of its rotating mass - which can act as a generator -
the stuff mentioned here is something completly different - but also
effects the dc motor on commutation - you turn off the current in the
coils - so you have some energy to vanish ... (....)


Charlie_V

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I don't think you need super conductors to make coils store more energy, you just need bigger coils with thicker gauge wires - of course you won't ever be able to match the field strength of a super conductor.  Besides, the energy storage in a coil is around 80-99 percent, not too shabby if you ask me.  Plus, if you start factoring in all the support equipment required to maintain 30 degrees Kelvin, the superconducting coil is probably worse than a regular coil. 

I'm not sure how else back-EMF is defined other than the way I defined it earlier.  Its the coil producing a magnetic field that opposes the applied field.  In a motor it causes the current in the coil to go to zero, by inducing a current in the coil that is in the opposite direction from the applied source current.  When the motor is loaded, the rotation slows down (known as slip).  This causes the back-emf to no longer cancel as much of the source current as it did at no load, and the source current is allowed to flow through the coil (consuming power from the source).  In generators it tries to stop the shaft rotation (which is almost always some sort of rotor with either magnets or electromagnets). 

What are some other ways of describing back-emf? 
« Last Edit: June 11, 2008, 05:25:44 AM by Charlie_V »

Charlie_V

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Quote
Besides, the energy storage in a coil is around 80-99 percent, not too shabby if you ask me.

By this I mean the coil's efficiency at storing energy.  It can be really good for properly designed coils.  Of course this value can be a lot lower too, depending on how the coil is made.

fritz

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A capacitor can maintain a charge for hours,
a "loaded", then shortened coil for seconds.
Because of the resistance - the current will
always decay (if not zero).

so what ?

If you measure after an hour - the capacitor has 99% charge,
the inductor 0% charge - efficency -infinite.

If I measure after 1ms, I got 100%:99.9%; depends on.

I

Charlie_V

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I'm not sure you can measure efficiency of a capacitor or coil based on time?  I'm not really sure how you can calculate that now that I think about it.  I guess it would be energy-in divided by energy-out.  So the amount of energy stored in a capacitor divided by the amount when it is discharged.  So for the coil, it will be the amount of energy stored in the magnetic field verses the amount of energy that comes out when it is shorted. 

I think time needs to be eliminated from the equation because once a capacitor is charged, the discharge could be nanoseconds or hours, but the same amount of energy will come out no matter what.  Same with a coil (accept the time constant on a coil is typically much shorter), but the same energy stored in the coil's magnetic field should be damn near the amount that comes out when the field collapses (minus some resistance in the coil).  Thats why with big wire gauges, the efficiency of the coil will increase.  500 feet of 10 gauge wire has about 0.5 ohms of resistance where as 28 gauge wire has 32.45 ohms.  The 10 gauge will be more efficient at storing energy but the coil will be larger.

Plus, another reason why we shouldn't involve time is that a rare earth permanent magnet can hold its field for an estimated 400 years, where as the best electret (look up electrets if you don't know what they are) can last MAYBE 20 years?  But the energy discharged in both at the end should equal the amount first stored in the beginning.  I think if you do the calculation these devices are close to 100% - pretty amazing if you ask me. 

The Observer

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Hello Again,

I have been studying the Back EMF and Energy stored in an inductor physics.

Quickly, a good example what an coil acts like with current is to imagine a waterwheel.
  When water flows, it take a while to get up to speed.
  Conversely, when potential stops( the water moving), it takes awhile to slow down.
   
I can visualize this effect as the wave of single electron passing through the coil would get to the next coil, before the electron,
   as the electron needs to go around a circle where the wave does not.
This must be where the initial resistance comes in.

Then as current is stopped... it's wave needs to still pass through the coil...this is where the back emf comes in.

Now I looked the formula that has to do with energy stored in an Inductor.
Henries I believe.

Anyways, the effect is negligible, without a ferromagnetic core.

By that I mean...The energy stored (it's inductance) can be 5,000 times greater if a ferromagnetic material is used as it's core.

  So, this does bring us back to MAGNETIC PERMEABILITY.
  5,000 times greater is significant.

Wish, I could elaborate... but, I must get going.

       Creativity is more important than knowledge - (thanks Einstein)
                                                                                                 The Observer
                           


fritz

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The inductivity increases with a core,
but you can squeeze more energy in a coil without
a core due to the fact that there is no saturation.

And anything curious which has somehow to do with a coil
and is to big that it fits in the head is Back EMF. of course.

sorry.

MinEth3r

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Hi The Observer,

You might find this interesting:
   THE PARAMETRIC POWER CONVERSION
       A STEP TOWARDS OVERUNITY......
Created on April 16th, 1997 - JLN Labs - Last update : January 10th, 2003
    http://jnaudin.free.fr/html/paraintr.htm

Also, this better EM theory might interest you 
http://newelectromagnetism.com

Also, a recent effort regarding the classical - been discussed so many times before - cap anomaly:
http://ringcomps.co.uk/doc/

Best wishes!

The Observer

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Hello Fritz,

You said,

The inductivity increases with a core,
but you can squeeze more energy in a coil without
a core due to the fact that there is no saturation.

I believe that is false.

Like I said, if you look at the formula, The MAGNETIC PERMEABILITY multiplies the energy stored or inductance.
Most Magnetic Permeabilities are about 1.
This doesn't do much ya know.... multiplying by 1.

  I will tell you what does though.
  Multiplying by 5,000 or more.
  The materials that do this are of ferromagnetic classification.

Saturation refers a point when the core can no longer add to the magnetic field of the coil.

That is, when a coil with a core becomes magnetized, the dipoles (and thus domains) start to line up with the field.
 With a very small current and magnetic field produced by the coil, only  few of the domains start to line up.
  This is where amplification  begins.
   Then there is a point, as the magnetic field of the coil increases (due to increased current), that all dipoles in the core line up.
    This point is called saturation.

   The current can be increased, but the resultant increase in magnetic field after saturation is as if there were no core.

Anyone exploring this... please consider what a coil does with air or any other material as it's core, then compare with a ferromagnetic core.
  This is the reason this thread exists.

May the Sun Shine on your Back Door,
                                                        The Observer
           


LDVAN

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Observer--

Pay heed to those who take the time to explain themselves and the theories they know. These gentlemen obviously KNOW about what they speak of. Your Degrees are impressive but they lack 'hands on' experience. Remember this 'grasshopper', youth and skill will never exceed old age and treachery.....  Listen to what you cannot see, look for what you cannot hear........

My compliments on your levels of education, now welcome to the real world

LDVAN

The Observer

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Hello LDVAN,

I am trying to conceptualize what is going on when a ferromagnetic core amplifies the magnetic field of a coil by over 5000 times.
    With this understanding I believe a machine could easily and simply be built that extracts the energy from the electrons
    that spin around the atoms of ferromagnetic materials.

I really do thank anyone who brings in any point, because it has led me to questions and research.
  Which has brought me closer to understanding this phenomenon.

My degree in Physics came 20 years ago, and I don't claim to remember the specifics of any given subject very well !
   But for the last month or so, I have been reacquainting myself some basic concepts as well as learning new ones.
     
I ask you LDVAN, to think about this, and tell me what you think.

A coil with a ferromagnetic core has a magnetic field 1000's of times greater than the same coil without the core.
   All this with no extra current or electricity.

There's a lot I would like to know about this.
  If you have any ideas, please impart.

I Bid You GoodDay,
                             The Observer

LDVAN

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Observer -- Read, and if necessary, re-read what has been told to you in this thread. Your questions were answered by people who, like myself, have had 'hands on' experience for the greater portion of their lives (or so it would seem by their writtings). I personally have over 50 years of learning to go with the 50 years of experience dealing with electricity and its effects. There is a bounty of information within these forums that cannot be purchased with any amount of money. One just needs to open the eyes, read and not feel that their way is the only way. Quit quoting, start understanding what is being explained to you. You are far, far from dumb. Use your knowledge to benefit from others knowledge. I'm not trying to be an ass hole here, you need to step back and look at the whole picture and what others are offering to you, free for the taking, no charge, nada dime.............

The more I know, the more I realize I don't know...........
LDVAN

LDVAN

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Now will somebody throw in some schooling on leading and lagging power factors (KW/KVA) to really set this boy in a tail spin...........

Best Regards
LDVAN

P.S. I read through the thread again start to finish. Observer, take down your blinders and absorb what these men are trying to tell you. You cannot buy what is being given to you for free, education from experience. Years of it. So read it again yourself, with an open mind !!

The Observer

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Hello LDVAN

   Thanks for your post.

      I am not sure how I pissed you off in regards to not listening to others, but I am damn glad you are interested in this thread.
      It sounds like you may be quite knowledgeable and I would appreciate anything constructive you have to say in regards to
         Magnetic Permeability and the possibility that it may have some real overunity answers based on Quantum Physics.

      As I have said, I have learned quite a bit from the comments.       Thank you !  to anyone who has posted or read this thread.
      If you say I am missing something or not comprehending correctly, then please tell me what I have missed.
       Perhaps, you could explain some of the important concepts as you see them and the things you have learned.
                                                        Mystery isn't going to help any of us.
                                                      That's how we got here in the 1st place.

For the last few days, when free, I have been exploring back emf or inductance.
  I have learned some, however I have come to realize that this is a tricky, perhaps misunderstood and maybe vague term.

More on this when I have a better grasp of what I understand it is, and more importantly isn't.

Imagine.
           The Observer