Voltage regulator is a "rectifier-regulator".
It is a "full wave rectifier" with 2 of the 4 diodes replaced by SCRs
(thyristors).
All output current is supplied through the 2 alternating sets of 1 diode
and 1 thyristor in series.
The voltage drop across these when they conduct (ideally zero)
determines the loss.
The peak current through these is a multiple of output current because
they conduct only a small fraction of the time. The peak current is
limited by the internal resistance of the alternator coils and the
internal resistance of the output storage capacitor.
See forward voltage at 50 A and 100 A for the SCR:
http://www.datasheetcatalog.org/datasheet/on_semiconductor/2N6504-D.PDF
See forward voltage at 50 A and 100 A for the diode:
http://www.datasheetcatalog.org/datasheet/on_semiconductor/MR2500-D.PDF
Ballpark voltage drop is 3 to 4 volts - 21 to 28% of output volts. Heat
dissipation as a percentage of output power (watts) is the same number.
From the datasheets it is clear that the voltage drop and therefore
loss percentage increases quite progressively with high and increasing
current.
If you can power a 40 W strobe directly from AC you may save 10 W or so
in heat generation in the voltage regulator.
Cheers,
Jan de Jong
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