Yamaha EF4500iSE Theory & Diagnostics Manual page 18

Yamaha Generator Theory & Diagnostics Guide
The EF1000iS
Exclusive to the EF1000iS, the double-coil system is
a unique design that adds to the main coil a second
coil specifically for running at lower rpm. Increasing
the number of coils in this second low-speed coil
enables it to generate optimum electricity when the
engine is running at lower rpm. When the engine
rpm increases, however, these extra coils become
unwanted resistance that reduced generating effi-
ciency. Thus, a system has been adopted that auto-
matically selects the right coil in relation to the
engine rpm; the low speed coil becomes the main
generating coil at low rpm and the main coil from
middle to high rpm. This is a Yamaha-exclusive tech-
nology that might be called a dual-stage system to
accommodate low and middle range rpm. The result
is a generating system that can provide optimum
electricity supply that is stable even at low rpm and
thus run with less noise and better fuel economy.
EF1000iS
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