On 01/20/2010 08:51 PM, Harry Veeder wrote: > > > > > ----- Original Message ---- >> From: Stephen A. Lawrence <[email protected]> >> 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. 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? > > Harry > > > __________________________________________________________________ > Looking for the perfect gift? Give the gift of Flickr! > > http://www.flickr.com/gift/ >
