Randall wrote:
>With generators, since the field is also part of
>the heavy iron housing, the housing becomes magnetized to some extent,
That small amount of magnetizism remaining is called "residual magnetism" and
must be there to start the generating process if there is no battery connected.
>BTW, I don't know how they do it now, but early AC alternators (like those
>used to generate power for your home) also required DC excitation as it's
>called. They used to actually run a DC generator from the same power
>source, whose only purpose was to supply the rotor current to the
>alternator. The field current to the generator controlled the rotor current
>to the alternator, which controlled the main output voltage.
Modern AC alternators (usually incorrectly called generators) powered by diesel
engines and the like, get their excitation from a small Permanent Magnet
Generator (PMG) that is on the end of the shaft. The output of the PMG is
controlled through the voltage regulator and fed to the excitor field which is
a rotating electro-magnet. It is virtually the same as Randall described, just
more efficient and no doubt cheaper to make.
Jerry Goulet
1960 TR3A
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