Re: But the Alternator Runs Anyway

[Larry Cartwright <exit60@CABLESPEED.COM>]

Ivan Rouse wrote:
> If you play with a small handheld generator that can power some small light
> bulbs you will notice that it turns very easily when no bulbs are turned
> on.  However when several bulbs in parallel are on it is noticeably harder
> to turn.  Therefore even though the alternator is turning all the time it
> will take more engine torque to turn it with the headlights on and thus the
> engine will do more work on the alternator to run the headlights and the
> gas consumption will definitely go up.

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
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"In theory, there is no difference between
 theory and practice. But, in practice,
 there is." - Jan L.A. van de Snepscheut