Self running coil?

[Tito L. Oracion]

delays, delays, delays. 

delays are bad trips in human attitude but they are very important to make a working self running coil. 

[gravityblock]

Hi Gyula,

The core is MP1305LF3T

http://www.metglas.com/products/page5_2_2_3_3.htm

The Finemet manufactured from Metglas is a (FT-3AH) and is a square loop core, http://www.scribd.com/doc/28763938/FineMet-Materials

I suspect the inductance is increasing until the core is right below the "knee" of the B-H Curve. Any further increase in saturation from this point, then the core's inductance will decrease.

This means if the magnet is placed at a distance where the inductance is the highest in this core material, then it will take very little input energy to fully saturate the core.

I pushed Finemet extremely hard in the main Orbo thread, but it did not get tested (if it did, then nobody released their test results).  Nanoperm, Metglas, and other square loop cores should have similar results.

Metglas and Finemet are sister companies.  There are restrictions when ordering Finemet, so there may be delays.  Here's an on-line inquiry form for Finemet, http://www.hitachi-metals.co.jp/e/cntct/indx_cntct2.html

GB

[gyulasun]

I'm no expert but if you can close to triple the inductance of a coil by introducing the center of a permanent magnet that sounds good to me.

One use I can think of is a PM attraction motor. The magnet is attracted to the Finemet toroid core (free work) and when it reaches TDC the coil is energized to release the magnets attraction to the A. Since you can close to triple the inductance of a coil using this Finemet core when the magnet is in the ideal location that it needs to be anyways for best results with this magnet motor design to work, the bonus will be that the coils electromagnetic field will be close to 3 times stronger without using more wire length which adds resistance and longer magnetic field reactance time.

It all looks like a win win situation for this kind of thing to me!

@Gyula, what do you think? Sounds like an ORBO

Luc

ADDED

One thing you may want to check is to what inductance the same length of wire can produce on a regular ferrite core of the approximate same size. If it's as high as you can get the Finemet using the magnet then maybe it's not all that great but if it's the same 25mH then I think this is very good. Please let us know of your results.

Hi Luc,

If the ORBO principle takes any advantage from core saturation caused by just the closeness of permanent magnets at a moment and this saturation helps reduce the input current need for reaching full or enough saturation to let the rotor escape from the attraction,  then the idea of increasing the inductance when the magnet(s) are close to the core sounds counterproductive because higher inductance demands higher input current to do saturation (if comparing to the previous ORBO example).  Somehow you have to defeat the extra flux the core possibly collected inside its volume from the strong magnet.
Of course this is what I think and the best would be to see the B-H curve of such core on a scope when the coil's self inductance on it has increased to a higher value due to a nearby magnet, how it would look like.

Maybe this inductance increase could be beneficial at your pulse coil in the oscillator because the copper loss could be decreased by using less wire for the given inductance needed for the oscillator. 

By the way, would you tell the DC resistance of the pulse coil you have used in your latest oscillators? I think it is the coil from a shaded pole motor and you tune it by a ferrite rod?

I wonder if you tried a normal toroidal core for the pulse coil between the gate-source electrodes? Or the toroidal core's tuneabilty by a magnet may  not give as a flexibility as the ferrite rod does?

Or a toroidal core has a much higher Q than the high DC Ohm motor coil and makes tuning (oscillating at all) very cumbersome?  I ask these because the resonant voltage across the gate-source surely depends also on the Q of the resonant circuit. Maybe you have found a certain low (or max a medium) Q value you have at present that  gives these <10uA results from the 3V and increasing the Q here would not be beneficial.

rgds,  Gyula

EDIT:  Luc, when I wrote on the higher current need for a higher inductance above I did not know this core has a square loop B-H curve. See my following letter to gravityblock too.

[gyulasun]

The Finemet manufactured from Metglas is a (FT-3AH) and is a square loop A, http://www.scribd.com/doc/28763938/FineMet-Materials

I suspect the inductance is increasing until the core is right below the "knee" of the B-H Curve. Any further increase in saturation from this point, then the core's inductance will decrease.

This means if the magnet is placed at a distance where the inductance is the highest in this core material, then it will take very little input energy to fully saturate the core.

I pushed Finemet extremely hard in the main Orbo thread, but it did not get tested (if it did, then nobody released their test results).  Nanoperm, Metglas, and other square loop cores should have similar results.

Metglas and Finemet are sister companies.  There are restrictions when ordering Finemet, so there may be delays.  Here's an on-line inquiry form for Finemet, http://www.hitachi-metals.co.jp/e/cntct/indx_cntct2.html

GB

Hi GB,

Thanks for the links, and if these cores has a square loop-like B-H curve indeed than I have to modify my previous letter to Luc because I did not consider in my answer to him the core type had a square loop curve.

Indeed then the coil wound on such a core would surely need a very little input current to get full saturation so that the magnet on the rotor could escape very easily from the attraction situation.

Thanks, Gyula

[teslaalset]

FYI, I have encountered same effects on MetGlas cores a few weeks ago.
So, it's not only FineMet that shows this effect.
And I would not be surprised if this effect also works for normal ferrite cores.

The external magnet changes the B-H curve of the core material.
Changing the B-H curve means changing the permeability curve, and thus changing the coil value.

Note, that the optimum distance between magnet and toroid is dependent on the current being used (e.g. to measure the coil value).
This means that optimum distance can be different between the measured situation and the real 'in use' situation.
Using a DSO can help you to easily optimize the optimum distance for the 'in use' case (optimize the maximum current delay to a voltage step to find the maximum coil value).