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Generators energy output

  1. Jun 2, 2009 #1
    i am asking about the generators we use in house when there is a power failure(now a days people use inverters)

    here goes the question
    suppose the generator is running (max ouput is 1kw) but we are using a electric bulb(100w)
    is it running in its max potential or using less fuel compared to when it is used tp light 10 100w bulbs
    if yes
    how does it know how much energy output is required
    if no
    how is the excessive energy dissipated it is too much energy to be be dissipated by sound and heat (then generators are very inefficient)

    awaiting answer
    Rohit Kumar Patra
  2. jcsd
  3. Jun 2, 2009 #2


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    Staff: Mentor

    Welcome to PF.

    It will use less fuel if only one light bulb is attached to it than if 10 are. It doesn't need to "know" anything - the generator runs at constant voltage and the resistance on the circuit determines the amperage. The amperage and voltage together determine the torque required to spin the generator and thus the fuel input required.

    That said, a generator is sized and matched with the engine that drives it. It is at its most efficient near its maximum output. As such, it won't use 1/10th the fuel with 1light bulb as with 10 - perhaps it only uses 1/5th the fuel. The extra energy is dissipated as heat: at best, about 2/3 of the energy of an internal combustion engine is dissipated at heat (at worst, all of it is).
  4. Jun 3, 2009 #3
    can you explain the following part to me
    "the generator runs at constant voltage "

    thanking you
  5. Jun 3, 2009 #4


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    Staff: Mentor

    Sorry, I'm not quite sure what there is to explain about that statement. Could you be more specific about what you don't understand about that?
  6. Jun 3, 2009 #5


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    Gold Member

    Generator voltage is based on RPM, most gas driven generators are designed to be driven at a steady speed of 3600 RPM.

    If no power is being drawn from the generator the speed will be steady and you can tell by the sound of the gas engine what is going on, if one bulb is turned on you can hear a slight momentary drop in speed, a governor senses this drop and automatically increases fuel supply to bring the engine back to the proper speed, as more bulbs are turned on this process repeats.

    If the load imposed on the generator is large enough, the gas engine can be stalled completely .
  7. Jun 4, 2009 #6
    thank you
    that's what i exactly wanted to know
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