On 6/29/07, Cedric Chang wrote: > > > > On Jun 28, 2007, at 2:07 AM, Vasile Surducan wrote: > > > > On 6/28/07, Cedric Chang wrote: > >> > >>> On Jun 27, 2007, at 10:06 PM, Vasile Surducan wrote: > >>> > >>> The key is not only the winding number/cross section (which is a > >>> problem of mechanical power versus efficiency) but the presence > >>> of the magnetic flux amplifier (brass tube as a support for > >>> windigs) and > >>> an end of the slug made from brass with a cone shape and perfect > >>> match into the > >>> negative cone of the ending brass tube. > >>> > >>> Inspire yourself from a high power DC relay design. The > >>> efficiency of > >>> such construct is huge compared with a poor iron slug. > >>> > >>> Vasile > >>> > >> Why brass ? > > > > Because it concentrate the magnetic field. > > I looked on the web and most folks said to use > ferromagnetic materials such as steel for the > magnetic flux concentrator. > > http://www.ee.surrey.ac.uk/Workshop/advice/coils/mu/ > http://www.ndt-ed.org/EducationResources/CommunityCollege/Materials/ > Physical_Chemical/Permeability.htm > > These indicate that brass is a bad choice. > > Did I miss some important info ? "Concentrating" the magnetic field is an english word with many understandings. Imagine a coil which must be perfect isolated from the rest of the world. The perfect cage will be a sandwich manufactured from: - one layer of permalloy - one layer of copper - one layer of permalloy - one layer of copper - one layer of permalloy I think the explanation for brass magnetic field "concentrator" is the same. There is an electric and a magnetic variable component even in a DC magnetic field (because always there is a switching moment). The magnetic component is concentrated using ferromagnetic materials. The electrical component must be converted by conductive material as brass or copper instead of being lost. And the electric component is quite huge on huge current or large inductance coils. I'm still searching for that coil, the plans dissapeared in the 16 bit windows era, but I remember I still have one... Vasile -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist