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  • AC vs DC newbie questions

    I don't know if the word transformer is correct, but I will use it here to mean converting from AC to DC and/or back again. I think that the key to the whole grid vs non-grid would include a hefty discussion on transformers. I am a computer expert and I know that computers convert (Transform) from AC to DC.

    To start off, here is my first question: Would household devices like fridge, washer - clothes and dish, TVs, stereos, lighting - led and fluorescent, be better off working off of DC and have a transformer only for the AC coming in from the grid? If so, why not have new house construction include this configuration?

  • #2
    Originally posted by trekjunky View Post
    I don't know if the word transformer is correct, but I will use it here to mean converting from AC to DC and/or back again. I think that the key to the whole grid vs non-grid would include a hefty discussion on transformers. I am a computer expert and I know that computers convert (Transform) from AC to DC.

    To start off, here is my first question: Would household devices like fridge, washer - clothes and dish, TVs, stereos, lighting - led and fluorescent, be better off working off of DC and have a transformer only for the AC coming in from the grid? If so, why not have new house construction include this configuration?
    The biggest motivation for using AC is that you can easily trade off between voltage and current using a totally passive device (a transformer). With DC you need to either use a motor generator (old fashioned and inefficient) or active circuitry (a DC-to-DC converter).
    The converter is inefficient and expensive. The transformer, consisting essentially of coils of wire and a steel core, is both efficient and relatively cheap for the amount of power it handles.
    DC converters also tend to fail a lot sooner and be less capable of handling short term overloads. For example, a transformer can commonly handle ten or more times its nominal current when it is feeding a motor starting up.

    When you get down to motors, AC allows you to build an induction motor that does not rely on a commutator and brushes to switch the magnetic field direction as the motor rotates or a control circuit which converts the DC to pulsed DC (similar to AC) as is used in electric vehicles.

    PS: An AC induction motor also runs very close to constant speed independent of load and voltage while a DC motor will typically require speed control circuitry.
    Last edited by inetdog; 01-02-2014, 08:39 PM. Reason: PS:
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Originally posted by inetdog View Post
      The biggest motivation for using AC is that you can easily trade off between voltage and current using a totally passive device (a transformer). With DC you need to either use a motor generator (old fashioned and inefficient) or active circuitry (a DC-to-DC converter).
      The converter is inefficient and expensive. The transformer, consisting essentially of coils of wire and a steel core, is both efficient and relatively cheap for the amount of power it handles.
      DC converters also tend to fail a lot sooner and be less capable of handling short term overloads. For example, a transformer can commonly handle ten or more times its nominal current when it is feeding a motor starting up.

      When you get down to motors, AC allows you to build an induction motor that does not rely on a commutator and brushes to switch the magnetic field direction as the motor rotates or a control circuit which converts the DC to pulsed DC (similar to AC) as is used in electric vehicles.
      Thanks inetdog!

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      • #4
        Originally posted by trekjunky View Post
        Thanks inetdog!
        You are welcome, and take a look at the PS I just added.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Originally posted by inetdog View Post
          You are welcome, and take a look at the PS I just added.
          Thanks again. I vaguely remember computer hard drives have speed circuitry.

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          • #6
            You have stumbled upon why Nikola Tesla and George Westinghouse ruled the electric market and made your life what it is today by J.P Morgan. Big embarrassment to Thomas Edison who is now owned by JP Morgan aka GE.

            Tesla discovered and invented are modern AC distribution system. It is very easy to generate with about any mechanical rotating device. All it takes is simple copper coils to step the voltage up or down to regulate, thus making it very easy and economical to generate and distribute unlike DC. Dc requires very complicated and expensive controls to generate and distribute. Edison tried with the first electric system in the USA to operate in NYC but it eventually failed. JP Morgan backed Westinghouse and took over the US electric market and eventually bought out Edison along with his patents, and buried him changing the name of his company to General Electric.

            Now you know the rest of the story.
            MSEE, PE

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            • #7
              Originally posted by Sunking View Post
              You have stumbled upon why Nikola Tesla and George Westinghouse ruled the electric market and made your life what it is today by J.P Morgan. Big embarrassment to Thomas Edison who is now owned by JP Morgan aka GE.

              Tesla discovered and invented are modern AC distribution system. It is very easy to generate with about any mechanical rotating device. All it takes is simple copper coils to step the voltage up or down to regulate, thus making it very easy and economical to generate and distribute unlike DC. Dc requires very complicated and expensive controls to generate and distribute. Edison tried with the first electric system in the USA to operate in NYC but it eventually failed. JP Morgan backed Westinghouse and took over the US electric market and eventually bought out Edison along with his patents, and buried him changing the name of his company to General Electric.

              Now you know the rest of the story.
              I remember seeing a documentary about Nikola Tesla and how he won the fight to light up the Chicago World's Fair one year. It didn't talk too much about why DC lost, but more about why AC won. But thanks Sunking!!!!

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              • #8
                Originally posted by trekjunky View Post
                I remember seeing a documentary about Nikola Tesla and how he won the fight to light up the Chicago World's Fair one year. It didn't talk too much about why DC lost, but more about why AC won. But thanks Sunking!!!!
                Yes and the irony is Westinghouse and Tesla beat out Edison and Morgan winning the bid for the Fair. Tesla used Edison's light bulb.
                MSEE, PE

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                • #9
                  Originally posted by trekjunky View Post
                  I don't know if the word transformer is correct, but I will use it here to mean converting from AC to DC and/or back again. I think that the key to the whole grid vs non-grid would include a hefty discussion on transformers. I am a computer expert and I know that computers convert (Transform) from AC to DC.

                  To start off, here is my first question: Would household devices like fridge, washer - clothes and dish, TVs, stereos, lighting - led and fluorescent, be better off working off of DC and have a transformer only for the AC coming in from the grid? If so, why not have new house construction include this configuration?
                  If you are a computer expert it must be with software expertise. Transformers are AC devices. You can google it.

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