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  • How long should absorb time be?

    Hi..I have a 48 volt 900 AH battery bank..8 Trojan 6 volt industrial batteries..just wondering how long should the absorb cycle take..currently have it set for 3 hours..manufacturer doesnt give any info on how long absorption cycle is..using Outback FM-80 charge controllers...thanks..

  • #2
    If you can calibrate the charge controller so that it knows the size of the battery, it can (not all can) caculate the Absorb time based on the time spent in Bulk. Otherwise, you have to sort of guess, 3 hours in Bulk, so I need to set 2 hours in Absorb. A hydrometer is the tool you need to test the cells with to see when they are full and you can stop Absorb.
    It's a tricky balance, and there is no "spec" because one person that discharges batteries to 40% drained, need a different Absorb time than if they were 70% drained.
    Clear as mud ?
    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

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    • #3
      3 Stage charging is useless in a Splar System. Not enough hours in a day. Trojan and Rolls have all changed charging profiles for Solar Users due to large number of warranty claims from solar users using 3-Stage charging. Set Bulk = Absorb = Float = 14.4 volts per 12 volt of battery. This will force your controller to stay into Constant Current Mode it battery voltage reaches 14.4 volts and then Absorb/Float until the sun sets.
      MSEE, PE

      Comment


      • #4
        Originally posted by Sunking View Post
        3 Stage charging is useless in a Splar System. Not enough hours in a day. Trojan and Rolls have all changed charging profiles for Solar Users due to large number of warranty claims from solar users using 3-Stage charging. Set Bulk = Absorb = Float = 14.4 volts per 12 volt of battery. This will force your controller to stay into Constant Current Mode it battery voltage reaches 14.4 volts and then Absorb/Float until the sun sets.
        Hi derek..so I am using the trojan industrial 6 volt 890 ah batteries..8 in total...im also using 2 outback FM 80 CC..a little confused about what you are saying..so how should i program my charge controllers? Are you saying should stay in bulk most of the time? I run 1 freezer and 2 refs--about 12 amps during the day then turn off at night so i do have loads while charging...thks much

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        • #5
          I am saying Bulk = Absorb = Float = 14.4 volts per 12 volts of battery. So for 48 volt battery set every stage to 57.6 volts. Your controller will then be a 2-stage CC CV charger. All Bulk means is Constant Current. Both Absorb and Float are Constant Voltage. In the morning the charge will pump in as much current as the panels can supply until the battery voltage reaches 57.6 volts. At that point as the batteries are roughly 80 to 90% charged up. The controller will hold the batteries at 57.6 volts assuming the panels can keep up with the load, and current will begin to taper off once they are fully charged up around sunset. Well that is if you have enough panel wattage to replace what was used over night and in the morning.

          Here is the issue. A standard AC powered 3-stage charge is a hard source with constant power 24 hours a day. Bulk is a Constant Current mode of say 50 amps on a 50 amp charger. ( Who knows about solar one minute from another) Once the batteries reach a set point voltage of say 56 volts the charger switches to Absorb by raising the voltage to 57.6 volts. Initially at the start of Absorb the charger is still pumping 50 amps. As the voltage of the batteries approach 57.6 volts the current will starts to taper off. You hold that 57.6 volts until the current tapers to 3% of C. On a 500 AH battery that would be 9 amps and it can take 4 to 8 hours. (Sun may have already set before you get to end of absorb). After Absorb comes Float which is another Constant Voltage of 52.8 volts. No current flows at Float other than equipment load demand current.

          Bottom line there is not enough sun hours for you to ever get to Float. So you pump in as much power as you can before sunsets. The issue comes up from RE users filling warranty claims against the manufctures. In all but a few cases sulfation caused premature battery failure. Sulfation is chronically undercharged batteries which account for 95% of all battery failures. Solar users are known to take care of their batteries and can at least show some records and voltage settings. They used the manufacture's 3-stage settings which were made for AC Chargers. Solar is not capable of getting the batteries fully charged with conventional AC charger settings.

          So Trojan Rolls, and quite a few others revised voltage settings for RE users to the Corrosion Side of the knife by raising voltages, and eliminating the 3-stage recommendations. Maintaining Lead Acid batteries is called dancing on the Edge of a Knife. One side is Sulfation where 95% of the people fall off of, the other 5% fall off the Corrosion side where battery manufactures are pushing RE users to dance. You stand a much better chance of making it to the end of the warranty period on the Corrosion side of the knife.

          Just keep a close eye on Specific Gravity and water levels. If Specific Gravity is running a little high, decrease the voltage a 1/10 a volt and give it a few days. Repeat until you get to where you need to be. Just don't fall asleep because conditions change week by week and should be part of your weekly preventative maintenance routine. Make damn sure you have a good quality Temperature Corrected Hydrometer and know how to use it. They cost less than $10.
          MSEE, PE

          Comment


          • #6
            Originally posted by Sunking View Post
            I am saying Bulk = Absorb = Float = 14.4 volts per 12 volts of battery. So for 48 volt battery set every stage to 57.6 volts. Your controller will then be a 2-stage CC CV charger. All Bulk means is Constant Current. Both Absorb and Float are Constant Voltage. In the morning the charge will pump in as much current as the panels can supply until the battery voltage reaches 57.6 volts. At that point as the batteries are roughly 80 to 90% charged up. The controller will hold the batteries at 57.6 volts assuming the panels can keep up with the load, and current will begin to taper off once they are fully charged up around sunset. Well that is if you have enough panel wattage to replace what was used over night and in the morning.

            Here is the issue. A standard AC powered 3-stage charge is a hard source with constant power 24 hours a day. Bulk is a Constant Current mode of say 50 amps on a 50 amp charger. ( Who knows about solar one minute from another) Once the batteries reach a set point voltage of say 56 volts the charger switches to Absorb by raising the voltage to 57.6 volts. Initially at the start of Absorb the charger is still pumping 50 amps. As the voltage of the batteries approach 57.6 volts the current will starts to taper off. You hold that 57.6 volts until the current tapers to 3% of C. On a 500 AH battery that would be 9 amps and it can take 4 to 8 hours. (Sun may have already set before you get to end of absorb). After Absorb comes Float which is another Constant Voltage of 52.8 volts. No current flows at Float other than equipment load demand current.

            Bottom line there is not enough sun hours for you to ever get to Float. So you pump in as much power as you can before sunsets. The issue comes up from RE users filling warranty claims against the manufctures. In all but a few cases sulfation caused premature battery failure. Sulfation is chronically undercharged batteries which account for 95% of all battery failures. Solar users are known to take care of their batteries and can at least show some records and voltage settings. They used the manufacture's 3-stage settings which were made for AC Chargers. Solar is not capable of getting the batteries fully charged with conventional AC charger settings.

            So Trojan Rolls, and quite a few others revised voltage settings for RE users to the Corrosion Side of the knife by raising voltages, and eliminating the 3-stage recommendations. Maintaining Lead Acid batteries is called dancing on the Edge of a Knife. One side is Sulfation where 95% of the people fall off of, the other 5% fall off the Corrosion side where battery manufactures are pushing RE users to dance. You stand a much better chance of making it to the end of the warranty period on the Corrosion side of the knife.

            Just keep a close eye on Specific Gravity and water levels. If Specific Gravity is running a little high, decrease the voltage a 1/10 a volt and give it a few days. Repeat until you get to where you need to be. Just don't fall asleep because conditions change week by week and should be part of your weekly preventative maintenance routine. Make damn sure you have a good quality Temperature Corrected Hydrometer and know how to use it. They cost less than $10.
            Ok got it..absorb is already on 57.6 so will set float to the same 57.6.during most of the year here in Philippines I can get 3-4 hrs absorb time even with my loads but that is about it..I usually discharge batteries more then 25%... I do have a good hydrometer and we check batteries every morning for SG and voltage...I realize that the voltage reading is not at all an accurate indication of SOC but just do it to confirm SG ..does this make sense? Thks

            Comment


            • #7
              Originally posted by Sunking View Post
              I am saying Bulk = Absorb = Float = 14.4 volts per 12 volts of battery. So for 48 volt battery set every stage to 57.6 volts. Your controller will then be a 2-stage CC CV charger. All Bulk means is Constant Current. Both Absorb and Float are Constant Voltage. In the morning the charge will pump in as much current as the panels can supply until the battery voltage reaches 57.6 volts. At that point as the batteries are roughly 80 to 90% charged up. The controller will hold the batteries at 57.6 volts assuming the panels can keep up with the load, and current will begin to taper off once they are fully charged up around sunset. Well that is if you have enough panel wattage to replace what was used over night and in the morning.

              Here is the issue. A standard AC powered 3-stage charge is a hard source with constant power 24 hours a day. Bulk is a Constant Current mode of say 50 amps on a 50 amp charger. ( Who knows about solar one minute from another) Once the batteries reach a set point voltage of say 56 volts the charger switches to Absorb by raising the voltage to 57.6 volts. Initially at the start of Absorb the charger is still pumping 50 amps. As the voltage of the batteries approach 57.6 volts the current will starts to taper off. You hold that 57.6 volts until the current tapers to 3% of C. On a 500 AH battery that would be 9 amps and it can take 4 to 8 hours. (Sun may have already set before you get to end of absorb). After Absorb comes Float which is another Constant Voltage of 52.8 volts. No current flows at Float other than equipment load demand current.

              Bottom line there is not enough sun hours for you to ever get to Float. So you pump in as much power as you can before sunsets. The issue comes up from RE users filling warranty claims against the manufctures. In all but a few cases sulfation caused premature battery failure. Sulfation is chronically undercharged batteries which account for 95% of all battery failures. Solar users are known to take care of their batteries and can at least show some records and voltage settings. They used the manufacture's 3-stage settings which were made for AC Chargers. Solar is not capable of getting the batteries fully charged with conventional AC charger settings.

              So Trojan Rolls, and quite a few others revised voltage settings for RE users to the Corrosion Side of the knife by raising voltages, and eliminating the 3-stage recommendations. Maintaining Lead Acid batteries is called dancing on the Edge of a Knife. One side is Sulfation where 95% of the people fall off of, the other 5% fall off the Corrosion side where battery manufactures are pushing RE users to dance. You stand a much better chance of making it to the end of the warranty period on the Corrosion side of the knife.

              Just keep a close eye on Specific Gravity and water levels. If Specific Gravity is running a little high, decrease the voltage a 1/10 a volt and give it a few days. Repeat until you get to where you need to be. Just don't fall asleep because conditions change week by week and should be part of your weekly preventative maintenance routine. Make damn sure you have a good quality Temperature Corrected Hydrometer and know how to use it. They cost less than $10.
              Ok got it..absorb is already on 57.6 so will set float to the same 57.6.during most of the year here in Philippines I can get 3-4 hrs absorb time even with my loads but that is about it..I usually dont discharge batteries more then 25%... I do have a good hydrometer and we check batteries every morning for SG and voltage...I realize that the voltage reading is not at all an accurate indication of SOC but just do it to confirm SG ..does this make sense? Thks

              Comment


              • #8
                Originally posted by larrybc1 View Post
                Ok got it..absorb is already on 57.6 so will set float to the same 57.6.during most of the year here in Philippines I can get 3-4 hrs absorb time even with my loads but that is about it..I usually dont discharge batteries more then 25%... I do have a good hydrometer and we check batteries every morning for SG and voltage...I realize that the voltage reading is not at all an accurate indication of SOC but just do it to confirm SG ..does this make sense? Thks

                Also derek how often should you EQ? Would seem like more is better...trojan says only wen SG differs...i do it once a month but maybe shud do it more...what do u think? Thks

                Comment


                • #9
                  Originally posted by larrybc1 View Post
                  I realize that the voltage reading is not at all an accurate indication of SOC but just do it to confirm SG ..does this make sense? Thks
                  Temperature Corrected SG is the only accurate real time SOC tool there is. No resting required can be done on active system. Only catch is Temperature Corrected.
                  MSEE, PE

                  Comment


                  • #10
                    Originally posted by larrybc1 View Post
                    Also derek how often should you EQ? Would seem like more is better...trojan says only wen SG differs...i do it once a month but maybe shud do it more...what do u think? Thks
                    No less is better. EQ is a controlled over charge which causes plate corrosion and flaking. Trojan has it right, only when it is needed as indicated by both voltage and SG falls out of tolerance range. If you charge by using you hydrometer as I lined out you will find you rarely need to EQ.

                    Once a month is one of those generic recommendations like battery voltages. Your hydrometer tells you what is really going on and what to do.
                    MSEE, PE

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