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Re: But the Alternator Runs Anyway



1 kWh of electricity requires on average 10,261 BTU to produce,
corresponding to a mean thermal efficiency of 33%. 1 barrel (42 US
gal) of gasoline contains about 5.3 MBTU. That's about 0.08 gal (10
oz) of gas needed to run the light bulb for an hour, not taking the
engine efficiency into account. A headlight is maybe 1/2 kW?
Wolfgang




Theoretically this is true. However, in reality an idling automobile
engine is using so much fuel to overcome friction and continually change
the momentum of the pistons and produce heat (lots of heat!) that I
doubt an additional 100-200 watts used by the headlights is even going
to be measureable in terms of the fuel consumption.

In some vehicles you can *hear* the additional load placed on the engine
by the alternator. If one is stopped at a traffic light with the turn
signals flashing, some engines will experience a slight change in
rotation speed every time the the lights flash on and off. I believe
this does not measurably affect the fuel consumption.

Best wishes,

Larry

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Larry Cartwright <exit60@cablespeed.com>
Retired (June 2001) Physics Teacher
Charlotte MI 48813 USA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"In theory, there is no difference between
theory and practice. But, in practice,
there is." - Jan L.A. van de Snepscheut