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  • #16
    Originally posted by Sunking View Post
    Average is meaningless, it what it consumes. With your information one could make a huge mistake and think all they need is a 250 watt inverter to run it. It would not work. You need the power it uses, and the energy it consumers over a period of time. Average power is worthless information that cannot be applied in any meaningful calculation.
    Average power consumption tells your how much energy a device will consume over any long period of time right away. This is exactly what you want to know to estimate energy needs. 125W will take 1250Wh in 10 hours, 3kWh in one day, 21kWh in a week, etc. This number has nothing to do with inverter power.

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    • #17
      Originally posted by Shmel View Post
      If I understand OP correctly, his monitor averages out power consumption over time. I.e. it is plugged in for 10 hours. During this time his fridge is running at 500W for 2.5 hours and idles for 7.5 hours. 1250 watt hours of energy are consumed during 10 hours, not 2.5, giving 125W of average power consumption. This number is displayed by the monitor.
      You can come up with fancy ways to explain the meter, but none are valid.

      The best monitoring meter I've met, is the Kill-a-watt, you plug an appliance in, and wait a week. It will tell you the watt hours that have been consumed. Raw numbers, then you can average them or whatever.

      Batteries should be measured in watt hours, and you should only use 20% of them in a day.

      500W x 2.5 hours = 1250wh consumed.

      For a fridge, you need to totalize the power over several days, to account for day/night usage, defrost cycles, and door openings.

      Inverter power is important, as the inverter needs to supply enough surge power to start the compressor motor, usually at least 5x the nameplate amps. Sometimes as much as 10x is needed to start a motor.
      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

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      • #18
        Originally posted by kimo View Post
        This makes sense to me and I'M a solar 1st grader. Thanks for explaining it in simpler language.
        You are welcome and as Mike points out you need to run the Kill-A-Watt Meter for a full week to get accurate useful data. For example you plug it in on say Saturday morning at 08:00 hrs and let it run exactly 1-week until the following Saturday morning @ 08:00. Then average it out for a full 24 hour day. So if the meter reads 14 Kwh consumed it used 2 Kwh/day and you would need a 10 Kwh battery.
        MSEE, PE

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        • #19
          Originally posted by Mike90250 View Post
          You can come up with fancy ways to explain the meter, but none are valid.
          The monitor manual explicitly says, that after 45 minutes of use it goes into averaging mode. It is quite evident, that it shows average power consumption by the load over period it was plugged in. To get estimation of how much energy this load will require over any period of time, you need to multiply this number by amount of hours. This is very simple.

          To determine the power of inverter which is needed to run the load, you need to know a peak power consumed, which this monitor does not record. But for a fridge you can estimate it by looking at instantaneous readings during first 45 minutes of monitoring when the fridge compressor switches on.
          Last edited by Shmel; 07-15-2012, 12:48 PM. Reason: bad wording

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          • #20
            I'm glad you got it figured out. I guess I was not much help.
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

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            • #21
              Originally posted by Mike90250 View Post
              I'm glad you got it figured out. I guess I was not much help.
              A. We still don't know whether the OP got what he needed, but the rest of us on the thread have satisfied ourselves that we understand what was happening!
              B. It's the thought that counts (although results are nice too!)
              SunnyBoy 3000 US, 18 BP Solar 175B panels.

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