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On 20 Nov 2001, at 21:57, Y and C Everhart wrote: > What I've noticed about coils are that coils filled with oil (shake them and you > can hear the oil slosh around) are usually the cheaper ones. The O.E. Bosch > coils and other good quality coils are epoxy filled (solid when shaken). I > won't use anything but Bosch, especially here in Arizona where the heat isn't > very good for the oil filled ones. I think the Bosch coils are also oil-filled, it's just that they are full, with no air space so they don't slosh. I'm not sure about this, though, they might just be filled with tar, but you will notice that they develop an oily region around all the seals as the years pass. There's nothing wrong with an oil filled transformer, in fact it's the best insulation money can buy. At my former job I designed, built, and tested a 1:1 230V power transformer isolated for 175kV. It was oil filled and worked like a charm. It's now a standard product for that company. Epoxy has all kinds of problems as an insulator: It expands and contracts at different rates from the parts inside and cracks as a result. The cracks become leakage and spark paths, and once sparked it leaves a track which never heals. The big advantage of fluid insulators is that they can't "track" so even if they spark they will heal. - Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ------------------------------------------------------------------- List info at http://www.vwtype3.org/list or mailto:help@vwtype3.org