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  • Originally posted by Naptown View Post
    I am brain dead today
    I need to convert 14.1 amps at 208v three phase to watt hours.
    Anybody know the formula?
    Is that 208Y/120? And the 14.1A is the phase line current, not the load winding current?

    If the voltage to ground is 120 and the current in each LN conductor is 14.1, balanced, the power will be 120 x 14.1 x 3, which is also the same as 208 x 14.1 x sqrt(3).

    If your 14.1 is the current in each phase-to-phase load, the power is 208 x 14.1 x 3, but the line current will be greater than 14.1 by a factor of sqrt(3).
    Now that you have watts, I will let you figure out the watt-hours, since you did not tell me the time factor.

    BTW, I find that the trick of multiplying the phase line current times the line to ground voltage and then multiplying by 3 is really easy to remember and gives the same result as the "official" calculation. If nothing else it is a good reality check that you got the other formula correct.

    There is no need to work with vectors and sines and cosines, since the amount of power going out the phase lines will be exactly the same for a given current regardless of whether the load is actually delta or wye. You just have to keep in mind which current you are measuring.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • One

      Pool has a 5 HP pump running 24/7
      This is for decorative and useless jets
      Trying to figure out savings by turning off
      This does not affect the filtration system as that is separate
      Last edited by Naptown; 11-01-2013, 06:40 PM.
      NABCEP certified Technical Sales Professional

      [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

      [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

      [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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      • Originally posted by Naptown View Post
        One

        Pool has a 5 HP pump running 24/7
        This is for decorative and useless jets
        Trying to figure out savings by turning off
        This does not affect the filtration system as that is separate
        You could also take a quick sanity check by multiplying 5HP times 746 watts if you assume that the motor is fully loaded by the pump. That will give you an upper limit.
        The measured current will probably be at a low power factor, and since you will not be paying POCO based on VA, you will have to estimate that factor.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • This is commercial so VA it is
          NABCEP certified Technical Sales Professional

          [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

          [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

          [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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          • Originally posted by Naptown View Post
            This is commercial so[B] VA it is[/B]
            Significant only if it reduces the max peak demand below the next lower surcharge level. Other than that quantity charge will still be based on watts.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • Originally posted by Naptown View Post
              I am brain dead today. I need to convert 14.1 amps at
              208v three phase to watt hours. Anybody know the formula?
              At our lab, we had a 3 phase bus. It was listed as 208 3 phase. But there
              was a common return, so you got 120VAC (to 100A) from a single line to return.
              Going on that, 14.1A from a 120V line to return =1692 VA, times 3 (lines) =
              5076 VA. Of course the net current down the return is zero.

              You can find what 2 equal currents 120 degrees out of phase = 14.1A total
              line current, (might be around 8.1A), multiply that by the line to line 208V
              times 3, better get the same answer. Bruce Roe

              Comment


              • I sell solar.
                No sale no income.
                Why I pointed out almost a 60% savings with almost no expense I have no idea. No sale for me.
                I have a bad habit ( for my income)
                of doing the right thing.
                Today probably cost me $5000 dollars by suggesting alternatives.
                Oh we'll I will sleep we'll tonight
                NABCEP certified Technical Sales Professional

                [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

                [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

                [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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                • Originally posted by Naptown View Post
                  I am brain dead today
                  I need to convert 14.1 amps at 208v three phase to watt hours.
                  Anybody know the formula?
                  va = amps x the three phase voltage x 1.73. Then you have to multiply by a power factor to get watts. Then multiply by the number of hours it is running.

                  So va = 14.1 x 208 x 1.73 x pf = watts. Your pf could be as low as 0.75 depending on the pump motor.

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                  • Since power factor is a loss wouldn't you divide by that?
                    NABCEP certified Technical Sales Professional

                    [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

                    [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

                    [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

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                    • Originally posted by Naptown View Post
                      Since power factor is a loss wouldn't you divide by that?
                      The power factor is the amount of watts divided by the volt amps. So watts = volt amps x the pf.

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                      • Originally posted by Naptown View Post
                        Since power factor is a loss wouldn't you divide by that?
                        No PF =< 1, and VA=>W.

                        VA = W/Pf
                        W = VA x PF
                        PF = W/VA
                        MSEE, PE

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                        • Originally posted by Sunking View Post
                          No PF =< 1, and VA=>W.

                          VA = W/Pf
                          W = VA x PF
                          PF = W/VA
                          Thanks Sunking. Formulas are so much easier to understand than writing them with words like I did.

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                          • I get it now

                            Originally posted by Mike90250 View Post
                            What's the difference ? Simplistically, Watts are for DC, and Volt-Ampres is it's AC equivalent. VA factors in the AC voltage & current when they are out of Phase, and is a more accurate standard of the energy being consumed.

                            Schneider Electric's APC division has many white papers & podcasts (see http://www.apc.com/podcast/ )
                            They are mostly trying to sell you a larger UPS, but the same factors are also present in off-grid housing, with CFL lights running off an inverter. Many CFL bulbs are.6 PF, which is really lame, when you have to have a lot of inverter overhead to run a little light.

                            Watts and Volt-Amps: Powerful Confusion (#15)
                            PDF: http://www.apcmedia.com/salestools/S...NQYF_R0_EN.pdf
                            MP3: http://www.apcmedia.com/podcast/content/wp/15.mp3

                            Enjoy.
                            Oh I understand now I was always confused with volts and watts

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                            • I've read about as much of this thread as I can possibly handle about carpenter's rules; two questions:
                              Does your power meter read true watts or VA?
                              What is the typical power factor of a residential load. My recollection is that equipment manufactures are supposed to keep Pf close to 1.

                              Finally I would gather if pF is off it is inductive so some capacitive trimming might be warranted in off grid. What works here?

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                              • Originally posted by posplayr View Post
                                What is the typical power factor of a residential load.
                                Not possible to answer other than generically of .7

                                My recollection is that equipment manufactures are supposed to keep Pf close to 1.[/QUOTE]
                                False. PF keeps going lower and lower with Switch Mode DC Power Supplies now used in all electronic equipment. Your laptop or PC is runing near .5 PF

                                Originally posted by posplayr View Post
                                Finally I would gather if pF is off it is inductive so some capacitive trimming might be warranted in off grid. What works here?
                                Nope capacitor banks are useless. Complete Snake Oil.
                                MSEE, PE

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