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Transformers, its current and its resistance

  1. May 5, 2012 #1

    Suppose a simple transformer, not connected to a circuit (just to the home AC). If we get a multimeter and measure its resistance we will get a number. So if we plug it into the home AC, it will consume energy (constant power).

    Now suppose we have a desktop computer power supply. Well, the desktop consumption varies: if we are playing a game, the video card is dissipating more power etc. So, I would imagine that if the desktop consumption raises, the desktop is not only consuming more from the power supply, but the power supply is also consuming more from the home AC, otherwise it will be a really huge non-optimized solution for power supplies. But I also know that the only thing connected to the home AC (if we look the power supply circuit itself) is the transformer, which is, in essence, an inductor (but acts like a resistor, it's a lot of cable, it has a resistance).

    Given this, the main question is: if the unique thing connected to the home AC is the coil of the transformer, and this coil has a resistance, which lets a I current flows, how could the power supply consume less or more power from the home AC?

    I think you all understand my question. Please, could someone give me a clear explanation on that?

    Thank you very much
  2. jcsd
  3. May 5, 2012 #2


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    Staff: Mentor

    I can't do a detailed explanation as I don't know enough, but I believe that the different items that are consuming power in the secondary windings circuit cause various levels of resistance in the primary circuit through counter EMF.
  4. May 5, 2012 #3


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    Staff: Mentor

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