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Eternal absortion, good or bad?

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  • Eternal absortion, good or bad?

    Hello,

    Eternal absortion approach comes from the fact that some people believe charge controllers (CC) don't allow enough time for the absortion stage to be 100% complete when charging a battery with solar, some CC come with preset time for absortion, say 120 minutes, 3 hours, etc., some CC don't say how they know it's time to end absortion and switch to float.

    The common thought is that when the current charging a battery get as low as 0,5% the amps hour of the battery (0,5amps for a 100Ah battery), it's time to end absortion and switch to float stage, and to reach that 0,5% can took easily 5 hours of solar charging, meaning most of the time there's not enough solar hours to get there.

    Thinking about this, some people say that, as long as your battery is cycled daily, it's safe to make Vabs=Vfloat, making in fact absortion stage last until sun goes down, this is called "eternal absortion".

    Do you think this is worth a try? I'm thinking about setting my CC to Vabs=Vfloat=14,4V in winter and 14,2V in summer, what do you think? thanks in advance.

  • #2
    The goal is to return 120% of the power that was consumed, back to the battery, in order for it to be recharged. (AGM, Gel = 105%)

    The trick is to accomplish that in the normal sun hours. if you have trouble with that goal, you need to reevaluate the design of your system and add more panels and possibly batteries.

    On a daily basis, you only want to consume 20-30% of your battery capacity.
    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

    Comment


    • #3
      Originally posted by Mike90250 View Post
      The goal is to return 120% of the power that was consumed, back to the battery, in order for it to be recharged. (AGM, Gel = 105%)

      The trick is to accomplish that in the normal sun hours. if you have trouble with that goal, you need to reevaluate the design of your system and add more panels and possibly batteries.

      On a daily basis, you only want to consume 20-30% of your battery capacity.
      Thanks, my actual battery has only 32% good (tested with those cheap chinese tester after 24 hours of "pulse repair"), it's a wet cell 80Ah 12V Japan made, so I made my calculations and if I buy a FLA 150Ah 12V battery I will use at most 30% of its capacity a day.

      But my main concern is that this new battery will be sealed because nowadays in my city I don't think I will find any refillable battery so I have to maximize the charge but avoid gassing at all cost, that's why I don't want to go higher than 14,4V bulk and that's why I want to be sure I get 100% recharge, forcing it with Vabs=Vfloat.

      This eternal absorption seems to work right now, I'm using 14,4V in my old battery and the charge at night lasts longer.

      Thanks.

      Comment


      • #4
        You should not use eternal absorb with sealed batteries, is my advice
        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

        Comment


        • #5
          Originally posted by Mike90250 View Post
          You should not use eternal absorb with sealed batteries, is my advice
          Ok, I respect your opinion, do you think the risk of gassing is too high?

          Comment


          • #6
            Yes, the gassing risk is real, and fatal to the battery.
            you can "fudge" it a bit, by raising the absorb voltage, which will drive more amps into the battery, but that also increases the risk of gassing once the battery reaches a state of fullness. You really need the published tech data from your battery mfg, and a reliable voltmeter to set this properly.
            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

            Comment


            • #7
              Originally posted by Mike90250 View Post
              Yes, the gassing risk is real, and fatal to the battery.
              you can "fudge" it a bit, by raising the absorb voltage, which will drive more amps into the battery, but that also increases the risk of gassing once the battery reaches a state of fullness. You really need the published tech data from your battery mfg, and a reliable voltmeter to set this properly.
              Thanks, I've decided not to buy a sealed battery but a flooded one. Winter is almost over and I can still use my old actual battery until March next year, that will give me time to save money and look for an FLA battery to buy, with it I can use eternal absorb or max bulk voltage to achieve the best 100% recharge every day and stop worrying about gassing. Thanks again.

              Comment


              • #8
                WDC sounds like you do not fully understand how a battery charges and what CC/CV mean. Not going to repeat myself here because the info is in the Stickies, but you set your charge voltage with a battery hydrometer. At th eend of the day, you check specific gravity, and then set the voltage accordingly. 99.9% of the time the batteries will be undercharged so you turn the voltage up and force your charge controller to stay in CC mode from sunrise to sunset or max smoke because you will never fully charge the batteries. Then once a week run and charge on a generator to fully charge the batteries which will take 12 to 24 hours on a genny. \\For those .001% users who designed the system correctly will be able top go much longer between genny runs because the system is sized to fully recharge most days.
                MSEE, PE

                Comment


                • #9
                  Originally posted by Sunking View Post
                  WDC sounds like you do not fully understand how a battery charges and what CC/CV mean. Not going to repeat myself here because the info is in the Stickies, but you set your charge voltage with a battery hydrometer. At th eend of the day, you check specific gravity, and then set the voltage accordingly. 99.9% of the time the batteries will be undercharged so you turn the voltage up and force your charge controller to stay in CC mode from sunrise to sunset or max smoke because you will never fully charge the batteries. Then once a week run and charge on a generator to fully charge the batteries which will take 12 to 24 hours on a genny. \\For those .001% users who designed the system correctly will be able top go much longer between genny runs because the system is sized to fully recharge most days.
                  Thanks Sunking, I have read the stickies a lot, and I know you are a huge fan of hydrometers, but I don't have one, I think I'll have to buy it. Meanwhile, I tested that "eternal absortion" doesn't work well for me now that is getting warmer here. I let my battery charge at abs=float=14,4V for ten days and, while it worked great charging the battery, the water level is descending fast, and the battery today got worm to touch, the problem is the place where I keep my battery= the roof space, it gets very hot at summer and very cold at winter, I made a polystyrene (5cm thick) box to put the battery in and it helps (today 38ºC outside and 28ºC inside) but it's not enough. Anyway, winter is ending in a few days and that gives me time, I changed the voltages to abs=14,6V and float=13,8V, my CC doesn't go higher in absortion but that will increase the bulk time and decrease absortion time, also decrease the loss of water while in float. I'm aiming to avoid sulfation like the plague and accept that corrosion will kill my battery some day, also I'm doing all this testing with my very old FLA battery so one day, when I buy a new one, I won't have to put it through all this. I know my "methods" are not the best but is fun to me to work this way and I'm always watching my system to avoid any risk. Thanks again.

                  Comment


                  • #10
                    Originally posted by wdc View Post

                    Thanks Sunking, I have read the stickies a lot, and I know you are a huge fan of hydrometers, but I don't have one, I think I'll have to buy it. Meanwhile, I tested that "eternal absortion" doesn't work well for me now that is getting warmer here. I let my battery charge at abs=float=14,4V for ten days and, while it worked great charging the battery, the water level is descending fast,
                    That is why a hydrometer is a must have item. Your running blond. Best $10 you will ever spend. If you are boiling off the water means charge is too high. Hydrometer would have told you that instantly. Back off the voltage and get a hydrometer.

                    MSEE, PE

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