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Old 02-08-2011, 07:06 PM   #18
PlainBill
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Default Re: Samsung LTN1785w Inverter and CCFL Voltages

I'm going to explain my thought process on the relative resistances, and the limitations of the measurements.

Wikipedia probably has an article on the process of making wire. Essentially copper ore is refined, cast into bars, then pulled through a die that is very slightly smaller than the bar. The resulting wire is drawn through progressively smaller and smaller diameter dies (with heat treatments taking place to keep it malleable) until it reaches it's final diameter. It then gets coated with varnish as insulation. Impurities, variations in diameter, etc, will affect the resistance, but these should average out.

Transformers are wound by placing a fixed number of turns onto a bobbin. This parameter is controlled carefully. A test technique is used that will detect an error of a single turn on a winding. And it is the turns ratio that is critical. Depending on the logistics of the winding facility, I would expect identical windings made from a single roll of wire to measure within 1%, possibly within .2%. Variations between winding machines, spools of wire from different lots, etc will increase the range.

The big variation is when company XYZ decides to wind 'equivalent' transformers as a substitute for those made by company ZYX. The wire will certainly come from a different production lot, the winders will be different, tension setting may be different, and a different gauge of wire may be used. However, it is the number of turns on the primary and secondary that are important.

In this case, it would be instructive to use a ring tester to check the transformers. I'd suspect that only two bad transformers would be found.

PlainBill
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