Magnetic Permeability ... I can't find anyone talking about this !!!!!

[broli]

I made a more in depth thread about energy gain by permeability change:

http://www.overunity.com/index.php?topic=8576.msg219635

[Xaverius]

@ Nueview and Observer, yes it's correct, it would be 10,000 more.  Please remember that L (inductance) is determined by many factors including the number of turns of wire, cross-sectional area, length, permeability, etc.  Also one Henry (L) is a very large value, most inductors do not have that high a value.  And last, think of an inductor with a very large rise time as a sort of semi-permanent magnet.  A permanent magnet would have a rise time of infinity.

Anyway, I am currently working on a project that involves a C-shaped EM.  It requires 6V and 2A.  This produces a flux density in the core of about 1T.  If the gap is shorted by a soft ferrous pole (non permanent magnet) then force is about 12 pounds and the distance shorted is about 7/16".  This produces about 50 watts output as compared to 12 watts input.  The relative permeabilty of the core is about 200.  So at relatively low ur a magnetic/electric circuit can be optimized to produce a super efficient electro-mechanical system.  Hope this can help with some of your ideas.

[nueview]

this relates allot to what john ecklin was attempting to get at with his motional magnetic field generators i built a few but stopped as there was something wrong permeability seems to go hand and hand with reluctance there is more field retention in a solid bar than a bunch of steel wire due in part to hysterisous.
also i have been looking at the coil formula and doing allot of thinking on it and it seems that a wire has a given amount of inductance be it straight or wound into a coil the wire diameter plays a part but not really the coil size it is one of the things i am trying to find the origin of such as when were and who came up with the formula and why. if you have come across this information it may help allot with the calculations.
Martin

[The Observer]

Xav,

Sounds like some interesting research you got going there... keep up the good work !

                       Ok... 10,000 times longer is enough for me to do the calculations.
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I calculated that a           l  =   1 meter long  Coil
                                        A  =  (.1)m² 
                                        N  =   2886 turns
                                        R  = 1 ohm
                                                                                             will have a rise time of 1 second.

              L = (uN²A)/l.        u = 1.2(10^-6)         t = L/R       

So throw in a Relatively Low Permeability core with a  u_r = 10,000

             L = u_r(uN²A)/l  (with core)                t = u_r(L/R)
 
You get 1 sec *10,000 = 10,000 seconds = 166 minutes = 2 hours 46 minutes.
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With no experimental data to back me up I emphatically say...

                                            A 3 Hour Rise Time???  No F__ing way ! 

So Super Perma Alloy with a permeability of 1,000,000 would take 300 hours? or around 2 weeks !  ?

                            I don't believe that for a second,... pun intended !
                            Heck, I wouldn't even believe a rise time of 1 day !
                            An Hour? Wouldn't beleive it !

                            I place my bets in the minutes to seconds category.
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Guess the only way to really know will be to do the tests myself.

With at home parts, I suppose I can make a core out of paper clips and estimate the u_r at 2,500 or so.
I have a bead on a cheap signal generator, so I am hoping that works out.

Good Day !
                   The Observer

[broli]

Xav,

Sounds like some interesting research you got going there... keep up the good work !

                       Ok... 10,000 times longer is enough for me to do the calculations.
--------------------------------------------------------------------------------------------------------------------
I calculated that a           l  =   1 meter long  Coil
                                        A  =  (.1)m² 
                                        N  =   2886 turns
                                        R  = 1 ohm
                                                                                             will have a rise time of 1 second.

              L = (uN²A)/l.        u = 1.2(10^-6)         t = L/R       

So throw in a Relatively Low Permeability core with a  u_r = 10,000

             L = u_r(uN²A)/l  (with core)                t = u_r(L/R)
 
You get 1 sec *10,000 = 10,000 seconds = 166 minutes = 2 hours 46 minutes.
-----------------------------------------------------------------------------------------------------------------------
With no experimental data to back me up I emphatically say...

                                            A 3 Hour Rise Time???  No F__ing way ! 

So Super Perma Alloy with a permeability of 1,000,000 would take 300 hours? or around 2 weeks !  ?

                            I don't believe that for a second,... pun intended !
                            Heck, I wouldn't even believe a rise time of 1 day !
                            An Hour? Wouldn't beleive it !

                            I place my bets in the minutes to seconds category.
------------------------------------------------------------------------------------------------------------------------
Guess the only way to really know will be to do the tests myself.

With at home parts, I suppose I can make a core out of paper clips and estimate the u_r at 5,000.
I have a bead on a cheap signal generator, so I am hoping that works out.

Good Day !
                   The Observer

You will probably not have to wait that long depending on your voltage. Mumetal will long been saturated before you hit the ohmic current limit or the rise time constant.

According to this: http://www.magnetica.fr/repository/Fig26.gif Mumetal reaches its maximum permeability at around 0.05 Oersted which is about 4 ampturns/m. With your coil data that becomes a current of 1.4mA, after that current has been reached the permeability starts decreasing. So if you want to keep that long rise time you will need to use a voltage of 1.4mV or lower. The rise time formula says nothing about saturation but you have to take it into consideration.