Roll Your Own Power-Transformers!

Jan Rowland

11/97

Roll Your Own Power-Transformers!

Laminations: One should locate a small transformer shop in your own, or a very nearby town of population, say, 100K or so, and make friends with the owner/operator, so you can go in there during workday hours, and "buy 2-1/8" of 1-1/4"-leg #24 E-I laminations". Some might sell such "by the E-I set", so, you might want to take a calculator with you, to figure how many times the 0.025" (#24) laminations fit into your req. 2-1/8", or the 0.0185 (#26). The latter is better, but might cost you more per inch of stack, and will take a bit longer to assemble. But for some "important" transformers, it might be worth the small difference. I have been told there is little measurable difference, using the thicker #24 laminations. Some also have #29, which is only 0.014" thick. There is a manufacturer, National Lamination Corporation, Des Plaines, IL (312) 763-7000. But they surely have at least a full box minimum, and the boxes I have seen at my nearest small transformer shop are around 200 lb.each!

Now,"coil window" in the laminations is something about which there is little choice. Oh, there are a couple of sizes where there is a difference in ratio between the coil window and the center leg width, but not all ranges, nor do I have any idea how to specify. But I do know that it seems all tile transformer windings I have done for a given "square centerleg stack" have just fit, just fine, with little wasted space (and very rarely not enough space!) So, the ol' boys who came up with the ratio between the core width and the window size certainly did so after much empirical data initially determined those values.

Don't forget, when out "buying iron", be sure to get two pair of "L-brackets" to fit whatever E-I set you are getting, to use as "feet" for your transformer. These also perform the more important function of holding the E-I stack together, once assembled.

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