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  • Absorbtion Time

    Is there a max Absorb time for AGM Batteries?

  • #2
    It is not a timed event. Absorb is a constant voltage and held until charge current tapers to 3% of C. It can take up to 4 to 10 hours. There are not enough Sun Hours in a day unless you have an over sized panel array. Fo solar you do not use 3-Stage Charge. If you try your batteries will always be under charged and die an early death.
    MSEE, PE

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    • #3
      Originally posted by Sunking View Post
      It is not a timed event. Absorb is a constant voltage and held until charge current tapers to 3% of C. It can take up to 4 to 10 hours. There are not enough Sun Hours in a day unless you have an over sized panel array. Fo solar you do not use 3-Stage Charge. If you try your batteries will always be under charged and die an early death.
      Thanks, Dereck!!!!! Appreciate your input as usual!!!!!! I have a goal and I'm working my way there!!! Thanks Bro you! Have been a great help!!!!!!

      Mike

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      • #4
        With both the Bulk and Absorb cycles, you need to return about 120% of the power consumed, back to the batteries. There are 3-5 sun charging hours in a day, maybe less in your winters.
        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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        • #5
          Yep - extended float *if you are cycling* is the way to go. With inexpensive controllers, they may have a built-in timer for absorb, like only 1-2 hours that is not user-adjustable. In that case, you can defeat the insufficient absorb by setting your float to the same voltage as absorb, and letting mother nature turn off the switch daily.

          It is important to note if you are in a cyclic or standby mode. Ie, if you only use your solar only the weekends, and your system is otherwise charging all week long, then yes, it would be a good idea to incorporate normal float voltage.

          For example, Deka / East Penn recommends no more than 12 hours absorb. You'll never reach that in a cyclic environment daily. But in standby / weekend warrior usage, a totally overblown absorb is not ideal. An "endless" absorb leads to premature drying of an agm, and eventually interior and possibly exterior corrosion.

          Heck, even the dinky Deltran maintainers made for agm's have a 8-hour absorb timeout in an attempt to really get it all in there. Oh yeah, Enersys / Odyssey have an 8 hour timeout for absorb if you don't have any accurate end-amp monitoring or coulomb counting. Simple.

          The big players all know that agm's get undercharged for the most part.

          So just know if you are in cyclic or standby service and change accordingly.
          Last edited by PNjunction; 08-27-2015, 04:00 AM.

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          • #6
            Originally posted by Svencool View Post
            Thanks, Dereck!!!!! Appreciate your input as usual!!!!!! I have a goal and I'm working my way there!!! Thanks Bro you! Have been a great help!!!!!! Mike
            Mike perhaps this will help you and others. Don't get to hung up on Charge Voltages when it comes to solar application because voltage does not really mean a whole heck of lot. When battery manufactures specify charging voltages, it is made assuming a you are using a stiff source of unlimited supply of commercial AC power where a complete charge cycle can be as much as 24 hours. See the flaw? If I had an AGM battery charged with Solar, and charge current is C/8 or less, I would start at the highest recommended voltage the manufacture specified. Example manufacture might state charge at 2.34 to 2.45 volts per cell, so for a 12 volt battery would be 6-cells x 2.45 volts = 14.7 volts. .................................................. .................................................. ........................................ How would you know if that is enough? Tough question with AGM because you cannot measure Specific Gravity. What you can do is a few hours after sunset is look at the resting battery voltage with no or minimal load being taken, and compare that voltage with what the manufacture SOC voltage charge. Example at 100% SOC you are likely looking for a voltage of around 12.6 volts at 100% SOC
            MSEE, PE

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            • #7
              Example at 100% SOC you are likely looking for a voltage of around 12.6 volts at 100% SOC
              Sound advice taking it to the highest *temperature compensated* voltage, assuming your battery is in good shape to begin with. For an at-rest value after a couple of hours, with an agm, a healthy one is usually resting somewhere between 12.9 to 13.2v, or 2.15 to 2.2v per cell.

              Fearing overcharge, many agm users undercharge. If you are temp-compensated, running a healthy cell to the highest rated voltage and holding it there when cycling should be no problem.

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              • #8
                PNJunction you would have to TRY really hard over charge an AMG battery on solar. Same goes for FLA, except FLA is easier to tell if you are over charging. You would have to be running really high charge C-Rates, with very little use in between charge cycles. Granted AGM batteries do not have the thermal mass of an FLA, it still takes a a lot of energy to heat up an AGM battery over a long period of time. .................................................. .................................................. ........................... It happens occasionally in Telecom/Data operations as they do use a lot of AGM, but their rectifiers can deliver C-Rates in excess 1C and it can take a couple of days to detect depending on the severity. .................................................. .................................................. ............ Best practice I and some others can come up with using AGM on Solar is a bit of hide and seek. Start by setting Controller voltages as high as possible, wait until after sunset, and see where you fall. Adjust accordingly until you zero in. As season and usage patterns change, one must make occasional tweaks .............................................. FLA is easy peasy, just check Specific Gravity as the sun sets.
                MSEE, PE

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                • #9
                  Originally posted by Sunking View Post
                  PNJunction you would have to TRY really hard over charge an AMG battery on solar.
                  I agree. Most undercharge, and for those that have problems, the battery has already suffered abuse and is not in a a normal state.

                  Consider that a "commissioning" charge on an Enersys SBS / Outback consists of 24 hours at 2.40v/cell upon receipt!

                  Not sure lesser agm's would handle that, but the trend is there - undercharging is a sneaky thing. Finding the balance between undercharge and wanton abandonment of using good batteries in the first place, temperature compensation, accurate voltage monitoring is key. It isn't hard, but frustrates the cheapskate.

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                  • #10
                    Very good info I appreciate the sound advice you guys have given me. I'm to the point I converted my battery bank to 24v series and now have been pricing GT Panels which I plan on purchasing next week. I use my system everyday so I am in a cyclic mode as far as that's concerned. I've attached a pic showing my daily usage. From the advice I have gotten here and read I need more panels and I'm shifting everything to GT panels. After I get my use out of these AGM's I will move to Flooded batteries as that is a better way togo.... Thanks again, guys!!!!

                    Mike
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