Self running coil?

[gyulasun]

Being new to electronics, if someone could point me toward how to build a circuit to see a B-H curve on my scope, I'll take video of the curve rendered by the core when under influence of the magnet and without.

My scope has the option of plotting via X/Y inputs.

Hi Folks,

Here is Naudin tests on this topic, see here, with video too:

http://jnaudin.free.fr/2SGen/indexen.htm#hysteresis

Also, some more info is here:

http://www.cliftonlaboratories.com/type_43_ferrite_b-h_curve.htm

rgds, Gyula

[void109]

I apologize if I'm just being slow to catch the explanation - but does any of this explain why the inductance **increases** with a specific proximity to the permanent magnet?

If I understand correctly, increased inductance indicates that more current is required to saturate the core?  Where does this excess current get stored?

[gyulasun]

I apologize if I'm just being slow to catch the explanation - but does any of this explain why the inductance **increases** with a specific proximity to the permanent magnet?

If I understand correctly, increased inductance indicates that more current is required to saturate the core?  Where does this excess current get stored?

Hi void109,

Sorry but I do not know for sure why the inductance increases for your FineMet core.  What I guess is that the paralell arrangement of the core with the magnet's facing side forces the core to 'collect' as much flux as its narrow square loop B-H curve lets, equally inside its full volume, this increases the B inside the core up to a maximum value beyond which saturation suddenly appears. I think it is important here that all the total  volume of the core be imposed to the (nearly homogen) flux coming from the facing magnet.
This parallel setup's behavior is in contrast to the setup where you approach a magnet towards the toroidal core from sideways (perpendicularly): in this case the magnet has the main effect only locally at and near the small volume of the core where the magnet is placed: strong flux, hence partial or full saturation can only be created in that part of the core.  It is like you would have created a virtual air gap in that part of the core you approached/attached the magnet to. Virtually you "open" a toroidal core if you saturate a small volume of it 'locally' by a strong (but small wrt the full core volume) magnet.  This is how I think.

Probably I made the confusion first I was not aware your core has a square loop B-H curve and answered to Luc that increased inductance normally needs higher current, comparing this to his ORBO example where just the opposite happens to the core: in the presence of the magnet the inductance gets reduced due to the core (local) saturation and less inductance has less 'resistance' to current flow than a higher value inductance has. I was thinking generally.

IF you excite a coil's core with current, the current is 'used up' by the wire loss (I²R) and is used up for rearrangeing the domains in the core from their random 'position' to an 'organised' one, the magnetic energy (that was created from part of the input current) is inside the core, the domains store it temporarily. When you switch the current off most of the domains tries to return to their original random state and 'release' the stored magnetic energy, this is the "collapsing flux's case" and this can be collected from the coil if you steer the suddenly induced voltage spike into a capacitor via a fast switching diode.

Maybe I answered you questions.

rgds,  Gyula

[gotoluc]

Well GB,

here is my update about the Finemet cores. Maybe no one got some because they are next to impossible to buy.

Metglas says their distributor is Elna Magnetics. I called Elna Magnetics and they have no stock, never had. You have to fax them a detailed purchase request and then they will look into it. So I called Metglas and the one person operating this business is away till tomorrow

This does not sound like an available item to me. Nothing else can be found!

User Peterae sent me a Toroid a month ago: http://uk.farnell.com/jsp/search/productdetail.jsp?SKU=3057010 
I was saving it for when I find the ideal winding I want. However, last night I decided to wind it using 1 meter of 30AWG 25mm wire on that core which gave 24 turns. The resulting inductance is 9mH which I found kind of high so I wound the same 1 meter of 30AWG 25mm wire on the ferrite toroid core that I have been using in all my tests and it gives 30 turns. Its inductance is 1.22mH.

I'm confused as to why there is such a big difference. Is it the little bit of extra mass? Peterae Toroid TX36/23/15-3E5: OD 36.30mm, ID 22.55mm, height 15.5mm, width 6.8mm compared to my Regular Toroid I have: OD 34.45mm, ID 20.0mm, height 11.95mm, width 6.85mm

If someone can help explain the difference that would be helpful and appreciated.

Thanks

Luc

[teslaalset]

Hi teslaalset,

thanks for posting your findings

Can you help me with what I would need to do to setup my DSO scope to measure this. I have no electronics background so I don't know. I've just been learning as I go. I would need an illustration or better a video tutorial as I learn much faster visually.

Thanks for sharing
Luc

Sure Luc,

Have a look at my posting at the Steorn discussion thread, posting #2849, here:
http://www.overunity.com/index.php?topic=8411.2835

In Fig 3 Scoop, bottom picture, the delay between the raising edge of the bottom signal (= the signal of the signal generator), and the upward curve of the middle signal in the picture (= measured value of the current through the coil) should be maximized to obtain the maximum coil value.

Some additional explanation of this measurement:
If you switch a voltage over a coil, the current through the coil always lags the start of the voltage step.
The larger the coil value, the larger the delay of the current.
So, by moving the magnet the delay can be optimized and thus the coil value.

Hope this helps. If you need additional explanation, let me know.
(at the time of these finding I used a CRO instead of a DSO)