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Old 19th Jul 2021, 10:07 pm   #1
Julesomega
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Join Date: Dec 2012
Location: Stockport, Greater Manchester, UK.
Posts: 1,503
Default What is a reasonable magnetising current for a mains transformer?

I have been testing some mains tfmrs to offer on the forum, and because I hate bangs and showers of sparks in my face I use a lamp limiter. The larger ones give a dim glow from a 60W bulb, but when I tried this one the lamp lit brightly. It is from some Japanese consumer equipment, I guess from the 80s or 90s. However the off-load output voltages seemed quite respectable, though after correction for the reduced input they seem a little high, at 31V, 27V, and 27.5V

These in turn seem unusual for consumer equipment, where one usually finds something like 30V C-T, 15V C-T and maybe 9V for a bit of glue logic. I suppose it could have a shorted turn on what should be a second 27.5V winding

I added another 100W to the limiter, whereupon both lit at the same brightness and the transformer buzzed loudly. I discontinued the test as violence alarms me

I see we have a 'sticky' thread in this section, Testing a transformer for shorted turns which also recommends the use of a lamp limiter but doesn't give expected values according to transformer size. My transformer measures 605035mm and weighs 0.6kg, which should give a power rating of at least 25W so I am guessing a nominal 30W. I wonder what is going on here
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