> Isn't the I-E stack of a conventional power transformer > just a rectangular > binocular core made out of steel?
Almost. It is impossible to grain orient the entire core, and there are core areas out near the corners that have very little flux but add weight and cost. Rounder cores are nicer. The performance difference depends on the particular core, how the core is configured or stacked, how conductors are arranged, and where and how we are measuring the flux. In an E-I lamination the normal stacking procedure is to alternate single or groups of laminations. E from one winding end, then E from the other end. The result of this is much less air gap because I's are sandwiched between E's at both ends. The result is very little air gap in the flux path. The more the manufacturer interleaves the E's and I's, the less flux leakage there is. Chokes on the other hand are generally made with the E's all from one side, and a little paper spacing all the I's from the E's. This makes an intentional air gap. The gap reduces tendency to saturate, and can actually increase inductance when dc current is present. It also causes very high levels of flux leakage. Boy Scouts within miles of a typical filter choke can no longer rely on their compasses. Toroids are not perfect. Over half of the wire in the winding is outside the window. Outside the hole, that wire adds a lot of resistance compared to the inductance! This is where the dual C core transformers come in. With a thick core, most of the copper is inside the window. Pound for pound and physical volume for physical volume, they have the best ESR performance. They are really nothing more than two toroids side by side with a common winding sharing both cores. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
