Voltage reading while under load

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  • Gdwats
    Junior Member
    • Jul 2017
    • 207
    #1

    Voltage reading while under load

    A) If drawing power at the rate of C/20, how low should one let the voltage of a 24V FLA bank drop before next charge cycle. Starting fully charged at 29V. I tried to word this so that size wouldn't matter?

    I've been seeing the voltage drop to 24.4 before unplugging stuff, but no way is the battery depleted to those standing voltage readings. Most of the time it is running (C/100)
    is the only way to determine this to run c/20 to 24.4, turn all off and wait for SV in a few hours, repeat? Is there a formula for this?

    B) my situation is 230AH 24v bank, running around 50W to 250W max at times. For the C, do we use rated charge of 230Ax24V = 5200W or half that? 5200/20 or 2700/20? Big diffence.
    900W, 40A MPPT, 230AH FLA,24V Samlex 1500W
    Tags: None
    • Mike90250
      Moderator
      • May 2009
      • 16020
      #2
      While under load, expect the voltage to read a bit lower than it would actually be. You will get a feel for how to adjust your readings.
      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
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        • Wy_White_Wolf
          Solar Fanatic
          • Oct 2011
          • 1179
          #3
          Originally posted by Gdwats
          A) If drawing power at the rate of C/20, how low should one let the voltage of a 24V FLA bank drop before next charge cycle. Starting fully charged at 29V. I tried to word this so that size wouldn't matter?

          I've been seeing the voltage drop to 24.4 before unplugging stuff, but no way is the battery depleted to those standing voltage readings. Most of the time it is running (C/100)
          is the only way to determine this to run c/20 to 24.4, turn all off and wait for SV in a few hours, repeat? Is there a formula for this?

          B) my situation is 230AH 24v bank, running around 50W to 250W max at times. For the C, do we use rated charge of 230Ax24V = 5200W or half that? 5200/20 or 2700/20? Big diffence.
          There is no canned answer or voltage that we can give you. Basicly, you need to learn your system and set the cutout voltage accordingly. So:

          1. Determine the maximum you want to drain the battery. 50%? 80%? Remember setting higher will limit battery autonomy.

          2. Get from the battery manufactures specs what the SG should be at that SOC should be.

          3. Run your load on the batteries until they reach that SG.

          4. Take voltage reading under that load. That will be your starting point and should be done a few times to get an average voltage.

          5. Recheck every 3mo to year to adjust to the aging batteries.

          WWW

            Comment

            • Gdwats
              Junior Member
              • Jul 2017
              • 207
              #4
              Awesome. Thanks.
              900W, 40A MPPT, 230AH FLA,24V Samlex 1500W

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