Quote:
Originally Posted by KU40
Most alternators create more electricity than the car needs, so a fair amount is wasted anyways.
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WRONG!
Most alternators (even very big ones) only produce what electricity is currently being "used" (either immediately, or to charge the battery), so little is wasted. While it is true that many car alternators are considerably "over sized" (and therefore could theoretically keep up with much more demanding electrical needs in the car), that mostly just has an effect on the maximum power you could (if you really wanted to) use from that alternator.
BUT, almost all alternators put progressively more drag on the engine, as your electrical usage goes up!
So even if/when you have a way "over sized" alternator, you will still end up using more fuel (due to the higher alternator drag) as you use more electrical power. And in the case of cars, the mechanical energy source is the engine, so as the engine "drag" from the alternator increases (as a result of using more electricity in the car) the engine needs to do more "work" (generate more mechanical energy) to compensate (which will usually result in the engine burning more fuel to accomplish this extra "work").
Of course, when you look at this from an electrical engineering standpoint, that result is really to be expected. After all, a car "alternator" is just one design for a mechanical energy to electrical energy "generator". And so the car's alternator, since it is a "generator" of this type, has to follow the same laws of nature that pertain to ALL such "generators". And since one of those laws of nature is that energy is just transformed from one form (mechanical motion) to another (i.e. energy is not "magically" created out of thin air), then it follows that the more electrical "work" (i.e. electricity) you get out the harder it will be for the mechanical source to turn the "generator".
BTW: This is the primary reason why you really can increase fuel economy some (in most cars), simply by taking steps to use less electricity in the car!
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