----- Original Message ----
> From: Stephen A. Lawrence <[email protected]>
> To: [email protected]
> Sent: Wed, January 20, 2010 10:26:24 PM
> Subject: Re: [Vo]:steorn addendum video posted on youtube
>
>
>
> On 01/20/2010 08:51 PM, Harry Veeder wrote:
> >
> >
> >
> >
> > ----- Original Message ----
> >> From: Stephen A. Lawrence
> >> To: [email protected]
> >> Sent: Wed, January 20, 2010 1:04:33 PM
> >> Subject: Re: [Vo]:steorn addendum video posted on youtube
> >
> >>
> >> As for the changing inductance in the changing external magnetic field,
> >> I don't think that happens while the power's on, because the core's
> >> being held in a saturated state by the field from the coil.
> >
> > Are you explaining how to electronically eliminate back EMF?
>
> No, not exactly. There's already no back EMF with a toroidal coil.
> (That's hard to show directly, but easy to show by conservation of
> momentum.)
> What I'm talking about is something a little different. When a strong
> external magnetic field acts on a ferromagnetic core, it may, if I
> understand this correctly, actually put the core in a "saturated" state,
> such that an additional B field which is aligned with the external field
> won't result in any additional magnetization of the core. If the B
> field of the core doesn't increase with further increase in the applied
> field, what that says is the *permeability* of the core has, in effect,
> dropped. The reduced permeability of the core means that the inductance
> of the coil will be lower when the core is in this state than when it's
> unsaturated.
>
> So, changing the external field will change the inductance -- IF the
> coil has no current flowing through it. But, the inductance of this
> coil is already not a fixed value; it varies with the current. When the
> current increases to the point where the core saturates, the inductance
> drops, because the permeability of the core material has (in effect)
> dropped. In the case where the core is saturated by the effect of the
> current in the coil, adding (or removing) an additional external field
> may have no effect on the core, which may very well remain saturated
> throughout the operation. In that case, the permeability won't change
> due to a change in the external field, and the inductance of the coil
> won't change.
Let me see if I have this right by re-expressing this in common language.
1) You _can't_ induce a current in a core-less toroidal coil by waving a magnet
outside the coil.
2a)You _can_ induce a current in a toroidal coil with a core by changing the
magnetic strength of the core by waving a magnet outside the coil...
2b)...but only if the core is in a state where it can absorb more magnetism.
Harry
> Clear? (As mud?)
>
> My grasp of saturation in magnets is pretty weak, unfortunately, and I
> may be exposing my ignorance here. Anybody with a better understanding
> of magnets want to correct this? Terry? Bill? Horace? Anybody?
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