Self running coil?

[gotoluc]

I'm still looking at inductances with various setups - I noticed something which I cant explain, I'm hoping one of you can.

I wound a new toroid (Finemet nanocrystalline - small, about 14mm in diameter).  Once wound it has an inductance of 250mH.  As I approach my large 2" dia magnet, its inductance INCREASES to a peak, and then begins falling off as expected.  The maximum inductance increase is found when the toroid approaches the north or south pole of the magnet, with the toroid parallel with the magnet (inner hole facing the magnets pole).  The increase goes from 250mH to 500mH before falling off.

What mechanism is causing the toroid to GAIN inductance by the presence of the permanent magnets field?  I thought I understood the lowering of inductance, I just dont understand the gain.

Hi void109,

I have a small 14mm toroid on hand and wound it with a very short wire giving me 750uH and can confirm that at a certain position I was able to make the inductance higher, The max I go it to was 925uH.

Your results are quite impressive. Can you give me some details on your 2" magnet. Is this a Neo, ceramic, how thick is it, grade, how close is the toroid?

I noticed if I tilt the toroid a little I got the highest results. Is it the same for you?

Thanks for sharing

Luc

[void109]

Hi - it is a neo 2" diameter .5" thick.  The toroid is about dead center on a pole side - roughly 12mm or so from the magnets surface

[void109]

I tried to find the same with many other toroids I had previously wound of various unimpressive cores - couldnt see the effect using another unaffixed 2" magnet.  Perhaps its a property of the core.

[gotoluc]

Hi - it is a neo 2" diameter .5" thick.  The toroid is about dead center on a pole side - roughly 12mm or so from the magnets surface

I also have a 2" Neo but it's 1" and N52. Quite strong so I have it about 2" away in center.

When you move it away from the center, how far down does the 25mH drop to?

Thanks

Luc

[gotoluc]

Perhaps its a property of the core.

Yes, that's why I would like to know how far down the inductance drops when the toroid is away from the center of the magnet.

Maybe these cores would be even better for what I'm doing

Anyone care to comment

Luc