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How does a car's loads affect it's fuel consumption?

  1. Jul 2, 2015 #1
    Hi, so I was wondering about how the car's LED, MP3/IPOD, AC systems consumes up electrical power and then to fuel?

    Let's say that the loads are running for 5-7 hours. Thanks for the replies/ideas!
  2. jcsd
  3. Jul 2, 2015 #2


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    Staff: Mentor

    Welcome to the PF.

    What is a car's LED system?

    And a car's air conditioning system (AC) power consumption is very different from any MP3/radio power consumption. Why may running the AC actually improve gas mileage?

    Do you know the conversion between horsepower and watts? :smile:
  4. Jul 2, 2015 #3


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    Staff: Mentor

    Also, what is the context of your question? Are you wanting to have some ammunition to make your kids turn off their MP3 players on long trips? :biggrin:
  5. Jul 3, 2015 #4

    jack action

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  6. Jul 4, 2015 #5


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    Running the cars AC system doesn't improve gas mileage. Failing to drive with the windows open improves gas mileage.
  7. Jul 7, 2015 #6


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    Had a friend that did not believe that lights influence consumption. A simple demo.
    Engine on. Lights off. Car in neutral. Look at the rpm meter. Turn on lights.
    The rpm will fall slightly from the drop in electrical resistance which puts more mechanical resistance on the "alternator" and as it is connected to the engine rpms get affected. And they rise back from more fuel given to the engine by the "regulator" (no idea of the terminology in EN).
  8. Jul 17, 2015 #7
    Any energy taken from the fuel that is not used to drive the wheels will increase fuel consumption.

    Anybody ever driven an old car that has an dynamo rather than alternator? Every time you switch on something, the car gets slower.....try it in the winter with the lights, heater, wipers on, any attempt to put on the radio and the car almost stops!
  9. Jul 17, 2015 #8
    when I first read this question I thought "It depends on the terrain and how many fat ladies".
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