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Amp Wattage Measurement - Approximations

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  • #61
    Do what the high power radio guys used to do: put a load resistor into a can of oil. Drive it with the output signal and the measure the temperature rise of the can of oil. This is probably best done by doing a "ballistic" test - insulate the oil can, measure its initial temperature, run the driving signal for a time much shorter than the thermal time constant of the oil can, then measure the final/peak temperature of the oil. A little computation gives the delta-T for the number of watt-seconds that were dumped into the oil.

    I'm all up on the calculation methods, use them all the time. But in the end power is about energy delivered to a load.
    Amazing!! Who would ever have guessed that someone who villified the evil rich people would begin happily accepting their millions in speaking fees!

    Oh, wait! That sounds familiar, somehow.

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    • #62
      Well, thatīs the State of the Art definition

      In fact there is a Victorian Era RMS Voltage (and current) meter

      Literally a "hot wire" type

      You have a piece of wire (probably Nichrome), stretched between a fixed point and a floating one, under tension by a strong spring, and the floating end drives a needle.

      Current through it heats the wire which stretches.

      You calibrate it by passing different DC current levels through it and marking the scale, which also becomes an RMS current scale by definition

      SMART Victorian Engineers indeed.

      Not kidding, I am very impressed by the incredible achievements of 19th Century Science and Engineering.
      We take Maxwell, Ohm, Kirchhoff, Oersted, Gauss, Boyle, Laws for granted, even Pascal which worked even 200 years earlier.
      Now for a minute imagine what tools and instruments, let alone calculation power they had available ... itīs mind boggling how much they achieved, with so little.
      Juan Manuel Fahey

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      • #63
        No need for calorimetric power measurement (which requires careful calibration) if it's audio frequency and a resistive load where voltage and current are in phase and PF=1.
        - Own Opinions Only -

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        • #64
          Originally posted by R.G. View Post
          But in the end power is about energy delivered to a load.
          Any other power except energy delivered to a load (continuous power) is a marketing figure.
          As far as I know, no one has designed an "perpetuum mobile" amplifier that, for example, has an input power of 100W but "supplied" the more output power than the input power.
          My comment about the power, refers to the amplifier does not apply to the loudspeaker

          At the end measuring the sound pressure level is the best indicator of the actual power that the amplifier delivers to load.

          Hamlet question
          It's All Over Now

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          • #65
            Originally posted by J M Fahey View Post
            We take Maxwell, Ohm, Kirchhoff, Oersted, Gauss, Boyle, Laws for granted, even Pascal which worked even 200 years earlier.
            Now for a minute imagine what tools and instruments, let alone calculation power they had available ... itīs mind boggling how much they achieved, with so little.
            Let's not forget Fourier, who in his short life figured out what he did, by heating up sheets of steel. No 'lectricity! Pretty amazing.

            Let's also not forget, when this RMS business became popular, @ 1972 when the Federal Trade Commission wanted hi fi and pro amp manufacturers to publish apples-to-apples comparisons of their amps. None of this "peak impulse power" or any other mumbo jumbo junk that was being touted by amp manufacturers of the time. Now, we're back to the bad old days. Pro amps that turn out a couple kilowatts, running off an ordinary 15 or 20 amp 120V AC line, baloney - where's the FTC now? What's the point of a 10 KW amp that can support that output for a whopping one millisecond? Spot welding anybody?
            This isn't the future I signed up for.

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