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  • Battery charging question

    Hi all....i was discussing with Sunking about how long the absorb time should be. He is saying that bulk=absorb=float...for a 48 volt system all should be set to 57.6.. Apparently there are a lot of warranty claims cuz with 3 stage CC batteries are not getting fully charged and causing early failure rate...i value Sunking's opinions as he is very knowledgeable... The question I have is has anyone gone to this basically 2 stage CC method and what are your opinions/results..it seems to be a radical method but does make sense..thks

  • #2
    Originally posted by larrybc1 View Post
    The question I have is has anyone gone to this basically 2 stage CC method and what are your opinions/results..it seems to be a radical method but does make sense..thks
    Technically it is not called 2-stage, just Constant Voltage with Current Limit. By setting Bulk = Absorb = Float turns your Controller into a Constant Voltage charger with Current Limit. But if you want to call it 2-Stage I am OK with it. The current is limited by the panel wattage.

    So in effect when the Sun rises your Controller goes to Current Limit aka Constant Current and pumps full power into the batteries until you reach the Voltage Set Point. Then it behaves like any Float aka Constant Voltage charger. At that point the panels can supply all the power assuming the load demand does not exceed what the panels can generate minus whatever charge current the batteries are still demanding as the float.

    The basic idea is to get the batteries charged up as fast as possible before yyou run out of day light, and/or generate as much power as possible into the batteries while you have sunlight if there is not enough time to get fully recharged.

    Trojan is anyone has noticed has changed their charging recommendations from 3-Stage to Daily Charge. They still leave some of the 3-Stage set points for those using 3-stage charges from the utility AC power. Commercial AC power has no time limit so it can fully recharge no matter what. You do not have that luxury with Solar.

    So take a look at Trojans Maintenance Guide and scroll down to Charging. Look at FLA the first one. Note there is no Bulk or Absorb. just DAILY CHARGE of 2.46 volts per cell. If you pull a Spec Sheet from one of the RE line of batteries like the T-105RE you will observe the spec sheets have not caught up with the new guidelines. So don't let the specs sheet fool you.

    Charging batteries is called Dancing on the Needle Head. On one side you have Sulfation (under charged) and on the other side you have Corrosion (overcharged). Solar users up to now have been on the chronic undercharge side of Sulfation. You need to go to the other side and flirt of Corrosion.
    MSEE, PE

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    • #3
      I would need to have auto water fill if I were to set mine any higher.

      My 24V system is set at

      29.4V Bulk,

      28V Absorb for 4 hrs, but it rarely stays on absorb for more than an hr or so.

      27V float.

      it is normally in float by 10am, and gasses freely in float.

      I have to top up at least 1 litre of water per week and sometimes up to 2 litres.

      Our average temp is around 25c, often daily 30c, nights 25c.

      7c is the coldest on record.

      They are now 8 years 10 months in service.

      Comment


      • #4
        Originally posted by Bala View Post
        I would need to have auto water fill if I were to set mine any higher.

        My 24V system is set at

        29.4V Bulk,

        28V Absorb for 4 hrs, but it rarely stays on absorb for more than an hr or so.

        27V float.

        it is normally in float by 10am, and gasses freely in float.

        I have to top up at least 1 litre of water per week and sometimes up to 2 litres.

        Our average temp is around 25c, often daily 30c, nights 25c.

        7c is the coldest on record.

        They are now 8 years 10 months in service.
        That is a pretty long life time for batteries. Over 3000 cycles.

        What is the voltage and Ah rating for each battery in your system?

        What has been you average daily DOD% over those 8 years?

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        • #5
          Having the batteries come up so fast tells me that either the system was originally oversized for the load and/or the batteries are sulfcated. They are not sulfcated enough that the system doesn't work just doesn't have the full storage capacity that the bank originally had.

          WWW

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          • #6
            Originally posted by Wy_White_Wolf View Post
            Having the batteries come up so fast tells me that either the system was originally oversized for the load and/or the batteries are sulfcated. They are not sulfcated enough that the system doesn't work just doesn't have the full storage capacity that the bank originally had.

            WWW
            That is what I am also thinking. Those batteries may still be working due to his small daily DOD% but they probably will not charge back up to 100% SOC of their nameplate rating.

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            • #7
              Originally posted by SunEagle View Post
              That is a pretty long life time for batteries. Over 3000 cycles.

              What is the voltage and Ah rating for each battery in your system?

              What has been you average daily DOD% over those 8 years?
              They are 4RP1800: http://www.allnaturalenergy.com.au/i...nergystore.pdf

              They would generally still be at 80% in the mornings. Never had a real deep discharge, if I am home like now and its raining, ( its early morning here) I have the genset going and charge them, wash some clothes pump water etc.

              Generally we have nice weather, sun is on the panels early winter or summer.

              From memory they were sized at 10kwh.

              Our worst time for night use would be summer, for refrigeration and fans where we may use 3kwh over night.

              Comment


              • #8
                Originally posted by Bala View Post
                I would need to have auto water fill if I were to set mine any higher.
                That is a possibility. Either your batteries have lost capacity, or you are one of the few with an oversized system. Most are chronic undercharged. The best way is to use a hydrometer to determine correct voltage. In lieu of that go high and if you use too much water back off the voltage. There is no one correct voltage that fits everyone.
                MSEE, PE

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                • #9
                  Originally posted by Sunking View Post
                  That is a possibility. Either your batteries have lost capacity, or you are one of the few with an oversized system. Most are chronic undercharged. The best way is to use a hydrometer to determine correct voltage. In lieu of that go high and if you use too much water back off the voltage. There is no one correct voltage that fits everyone.
                  After some discussions and thought a few months ago I backed off settings, thinking overcharge, and to save water.

                  I found I lost capacity, and fell out of equalization which they had not done for a long time. So I equalized and put all the settings back to the original and will leave them as they have been all the time.

                  Comment


                  • #10
                    Originally posted by Bala View Post
                    I would need to have auto water fill if I were to set mine any higher.

                    My 24V system is set at

                    29.4V Bulk,

                    28V Absorb for 4 hrs, but it rarely stays on absorb for more than an hr or so.

                    27V float.

                    it is normally in float by 10am, and gasses freely in float.

                    I have to top up at least 1 litre of water per week and sometimes up to 2 litres.

                    Our average temp is around 25c, often daily 30c, nights 25c.

                    7c is the coldest on record.

                    They are now 8 years 10 months in service.
                    on my other thread about keeping batteries charged in winter i set my bulk to 29.6v many replies reckon im going to wreck my batteries at that voltage but yours are doing ok at 29.4v it seems... sunny queensland. my experience so far been only 4 weeks , finding the solar panals a bit useless down here in NSW. been cloudy most days. thinking of selling the spare panels and buying more batteries and just charging them of the gen

                    Comment


                    • #11
                      Originally posted by almac View Post
                      on my other thread about keeping batteries charged in winter i set my bulk to 29.6v many replies reckon im going to wreck my batteries at that voltage but yours are doing ok at 29.4v it seems... sunny queensland. my experience so far been only 4 weeks , finding the solar panals a bit useless down here in NSW. been cloudy most days. thinking of selling the spare panels and buying more batteries and just charging them of the gen
                      As soon as mine hit 29.4 they drop to absorb, they dont stay at 29.4.

                      Why dont you just get the grid reconnected, I would love to have grid power

                      Comment


                      • #12
                        Originally posted by Bala View Post
                        As soon as mine hit 29.4 they drop to absorb, they dont stay at 29.4.

                        Why dont you just get the grid reconnected, I would love to have grid power
                        i would but so far nothing from ausgrid re repairing the damage they are responsible for. could take time. do you have flooded lead acid batteries? if so all the others saying 29v+ will cook your batteries are wrong. i shall put mine at the same bulk voltage works well for you

                        Comment


                        • #13
                          Originally posted by almac View Post
                          on my other thread about keeping batteries charged in winter i set my bulk to 29.6v many replies reckon im going to wreck my batteries at that voltage but yours are doing ok at 29.4v
                          You are not going to wreck your batteries. That is just plain ole silly.

                          If you want an exact voltage, then you are going to have to use a hydrometer. In Summer months you will find you have to lower your voltage a bit assuming you have enough panel wattage to get you fully charged up. The thing with solar there is not enough Sun Hours to cycle through each stage. As I pointed out and gave you a link manufactures are changing their recommendations for Solar Users. Instaed of Bulk/Absorb/Float they only state Daily Charge and Finnish Charge. Depending on manufacture Daily Charge is around 2.47 vpc or 29.7 volts on a 24 volt battery. Finnish Charge is even higher at 2.5 to 2.55 vpc.

                          Keep in mind those are all Recommendations, not Absolutes. To find the exact voltage is going to require you to use a Temperature Corrected Hydrometer. Take the SG reading when you see your Controller is near the end of the Absorb Charge after current has tapered off. If the SG is low, raise the voltage. If SG is high you should notice gassing and need to lower the voltage a bit. You will find the sweet spot. But don't think you are done. Because as season changes so will the Sun Hours and you will have to adjust. You will notice in Winter months the voltage has to be higher than Summer. Measuring SG should be part of your weekly preventive maintenance and make adjustments accordingly.

                          Bottom line is you want to error on the side of overcharge and avoid undercharging. Under charged batteries die faster than over charged. Just keep your eye on SG and water.
                          MSEE, PE

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                          • #14
                            Originally posted by almac View Post
                            i would but so far nothing from ausgrid re repairing the damage they are responsible for. could take time. do you have flooded lead acid batteries? if so all the others saying 29v+ will cook your batteries are wrong. i shall put mine at the same bulk voltage works well for you
                            What works for mine may or may not work for yours.

                            Mine are a dedicated RE battery that cost $7k nine years ago and weigh 160kg each.

                            Comment


                            • #15
                              Originally posted by Bala View Post
                              What works for mine may or may not work for yours.

                              Mine are a dedicated RE battery that cost $7k nine years ago and weigh 160kg each.
                              Those 4RP1800 4volt 1200AH batteries you have are pretty serious.

                              Looks like they should last those 9 years you have had them but may now be close to dropping off the table. Hope you get another year out of them.

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