Re: Saturation:(Was Rebuilding an OBIT)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

>Richie and Ed,
> 
> Thanks for the info, this is very encouraging news to me!, but unfortunately
> it also raises another question:
> If current does not saturate cores, why do people have problems with
> saturation when they try to use an unmodified variable autotransformer as a
> current limiting device? Is some incredibly high voltage developed on the
> rest of the winding when only a small part is tapped to allow more current,
> or is there some other gremlin at work here?
> 
> Thanks,
> Sue

	You got it right the first time!  The transformer has turns and core
area to handle it's rated voltage and no more.  If you turn the brush to
tap across fewer turns the voltage across those turns goes up and the
core saturates!  To avoid core saturation, the voltage across THE WHOLE
WINDING, not THE TAPPED PART, must be no more than a few percent above
the rating.  Since I've never tried to use a variac for ballast, I am
only guessing but think that at least in some cases what the guys are
using is really a variable saturable and saturating reactor, with
results I don't know how to analyze.  Sure someone experienced will have
something to say on the subject.

Ed