In article ,
Tim Lamb wrote:
Generator efficiency will presumable vary with load and I wonder if the
overall performance tails off as the battery approaches full charge?

Very much so. An IC engine running at a given speed has near fixed
friction and heat loss. If at a low throttle, pumping loses are greater
too. So the efficiency is much less than for a higher output at the same
engine speed.

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*Growing old is inevitable, growing up is optional *

Dave Plowman London SW
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