From: George Tyler >I have done a lot of transformer and inductor design over the years, always >said "you can't focus or direct a magnetic field", apart from ordinary >magnetic materials of course. On day I found something that someone had put >together on the web: He pointed out that if you have a resonant coil in a >magnetic field then the field it creates cancels the field around the >outside, and enhances it in the center on the coil. The effect is just like >"sucking" in the field into the coil!
That's true. You get the same effect just by having a long solenoid coil, where every turn has the same current in it. The magnetic flux travels all the way to the end, and then loops back around to the far end. Or a similar effect can be observed in a toroid, which can be looked at as a long solenoid coil, bent into a donut-shaped loop. However, that's not very helpful when you have a primary and a secondary, unless you can put one winding on top of the other (so all the flux lines link both coils). The resonance effect can make the flux lines link, because again you can make the current and phase in both coils identical. But then you can't extract any power from the second coil. :-) One other technique is to surround the transformer with a very good conductor; like wrapping it in thick copper sheet. The copper shorts out the magnetic flux, forcing it to stay away and flow along the other path you would prefer. You'll see this done on transformers in high quality audio gear, to "shield" or block the magnetic field from escaping to cause hum in the audio. Vicor uses this same trick to squeeze a little more efficiency in their switch mode transformers. -- Excellence does not require perfection. -- Henry James -- Lee A. Hart http://www.sunrise-ev.com/controllers.htm now includes the GE EV-1 _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org For EV drag racing discussion, please use NEDRA (http://groups.yahoo.com/group/NEDRA)
