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Re: Some days I hate this thing.......



> Original Poster: "Christopher Boden" <chrisboden-at-hotmail-dot-com>
> 
> We fried the NSTs in the second run, and cannot get the same performasance
> with enough 15/30's stacked to cause our utility company to run an extra
> shift. WHY???!!!!!!
> 
> Last time I checked the mathematitions told me that 2 15/30 NST's are the
> same as 1 15/60....but then again these are the people who brought us the
> spherical cow.

You're assuming that all the transformers are capable of delivering the
nameplate-rated number of milliamps at the *same voltage* under load, and
I'm not sure this is ever true. If you can, check that all windings of all
transformers are intact and measuring the correct output voltages (not
shorted or dead).  And have you actually measured the short circuit currents
from the transformers?  I have some "30mA" transformers that put out 24mA
when shorted, and I also have some "60mA" units which deliver 66+.  The
nameplate ratings are not usually accurate, and it varies by brand and by
production run.

There are other 30mA vs. 60mA transformer issues too: the 30mA transformers
are likely not as power efficient as the 60mA ones.  Two 30mA transformers
have more core material than a single 60mA unit, more shunted (wasted) flux,
and also probably dissipate more power thermally in their smaller gauge
primary coils (sometimes they have aluminum primaries even, a cost issue).
I've never sat down to work the math out exactly, but I've seen the results
you describe, and now I spend money on only 60mA NSTs.

In short, the 60mA transformer is not a simple linearly scaled-up version of
the 30mA transformer; there are differences in efficiency and
performance/cost ratio.

-Adam
adamsmith-at-mediaone-dot-net