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  • charge controller settings

    Hi,
    New to this forum and I've a question;
    I use 8 Cosco 6v GC batteries wired 4x2 for 24 volts and 440 AH. They are reasonably new and very cold in an insulated box in an uninsulated shed here in the upper Midwest.
    The panels are Salvina 270's and wired 3x2 for 1600 watts max. The charge controller is a Midnight 150 classic with the new software update.. I have had several different opinions on charging voltages. Some say use as low a voltage as you can to get to float, then use a higher voltage once a week to stir things up. Others say use a high voltage all the time.
    What voltage settings should I use for Absorb, Float and equalize? Keep in mind that due to the cold batteries, the Midnight will add 2 volts to whatever I set.
    Thanks

  • #2
    Originally posted by Retreat12 View Post
    the Midnight will add 2 volts to whatever I set.Thanks
    It should not unless you have AGM selected with temp compensation. Ambient temps have little to do with what voltage you select. Charge voltage does lower as temps rise, but that only applies when you get above 80 degrees. When it is cold you lower the charge rate (current), but voltage does not compensate, not do you have to worry about it because Solar charge rates are LOW enough to start with. So who ever told you to raise the voltage when cold should be ignored.

    You are being told Half Truths, but first can you tell me the make and model of the batteries for a detailed correct answer?

    Generic answer is Bulk = Absorb = 2.4 volts per cell
    Float = 2.2 vpc
    EQ = 2.58 vpc but only EQ when specific gravity is lower than 1.23, or wide ranging specific gravity 0.050 between the battery’s cells. That means rarely. Who ever told you once a week should be ignored.
    MSEE, PE

    Comment


    • #3
      Response

      Thanks for the response.
      The batteries are Cosco 6 volt Golf Cart @ 220AH. Flooded. They do not list a manufacturer and will not tell you.
      The Midnight controller has a temp compensator built in and I've left it on as batteries perhaps need that additional voltage when cold. There's a temp. sensor attached to a battery. I just let the reader know it was there.
      Thanks for the rest of that info.

      Comment


      • #4
        FWIW the Costco battery is made by Interstate. Temperature compensation is only used on AGM batteries to help prevent Thermal Runaway. It is of no use on Flooded Batteries and will do more harm than good. Flooded batteries are charged at the same voltage from room temperature to -40.

        What does change is the battery capacity when cold. At 10 degrees when fully charged up Flooded and even AGM will be roughly at 50% rated capacity. But there is nothing you can do about that except account for it. Otherwise disable Temp Compensation on your controller and use the voltages I specified, and you are good to go.
        MSEE, PE

        Comment


        • #5
          Response

          Originally posted by Sunking View Post
          FWIW the Costco battery is made by Interstate. Temperature compensation is only used on AGM batteries to help prevent Thermal Runaway. It is of no use on Flooded Batteries and will do more harm than good. Flooded batteries are charged at the same voltage from room temperature to -40.

          What does change is the battery capacity when cold. At 10 degrees when fully charged up Flooded and even AGM will be roughly at 50% rated capacity. But there is nothing you can do about that except account for it. Otherwise disable Temp Compensation on your controller and use the voltages I specified, and you are good to go.
          Thanks again,
          I'll do as you suggest. Nice to have some expert advice for a change. I've been talking to the Midnight people and others and it was all seat of the pants and vague as a violet stuff. I was going to ask your qualifications, just in case, but see you're PE in EE so I'll trust that.

          Comment


          • #6
            I've been trying to crack this nut myself. I have a 200 classic and 8 Trojan T-605 batteries. My setup is not climate controlled either since it powers a remote garage. On initial setup, I followed the T-605 data sheet settings of ab 2.35-2.45, float 2.20 and eq 2.58 I also hooked up and activated the battery temp probe that comes with the midnite. Also followed Trojan tech advice and set absorb time to 3 hrs but my SG has alsways been low and the midnite will drive the ab voltage to 58.x on cold days. I actually had to turn down the temp comp set point because the default will allow the midnite to compensate the ab voltage to the eq setting if you don't change it.
            Trojan says the SG at full charge is supposed to be 1.280 but i've never seen that. I upped the ab time to 4 hours at 56.4v and that seems to be helping but my SG still is mostly 1.20-1.22 after the ab is finished.
            I don't really know what to do at this point, if I eq the batteries they get up to 1.25 but they are right back to 1.20 after the next days ab is done. I've almost stopped worrying about it but I'm going to disable the temp comp now thanks to Derek. The batteries use hardly any water at all, between the 8 of them I MAY add 8 onces a month but probably closer to 8 ounces in 6 weeks.

            Derek, what would you recommend I do differently here, if anything.
            1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

            Comment


            • #7
              Originally posted by thastinger View Post
              Derek, what would you recommend I do differently here, if anything.
              When you take Specific Gravity reading are you using Temperature Correction hydrometer and tables?

              The specific Gravity in Trojan and any battery for that matter list it at 80 degrees. As temp goes down so does specific gravity. Correct the specific gravity readings for temperature by adding 0.004 for every 10°F (5°C) above 80°F (27°C) and subtract 0.004 for every 10°F (5°C) below 80°F (27°C). Keep in mind the temp is the electrolyte temp, not air temp so you will need a good thermometer made specifically for batteries.

              For example if the temp is 30 the Specific Gravity should read 1.24 at 100% SOC. At 0 will read 1.228. So make sure you understand that correlation and put it into practice. Note that EQ is a OVERCHARGE condition and does damage to the plates which is permanent. So only EQ when instructed to do so. Also understand as the temp drops, so does capacity. Use Trojan chart to see how much.

              Hope that helps.

              EDIT NOTE:

              I do not care for 3-stage charging for solar applications because there are not enough hours in a day to do it properly, and EQ is impossible with solar because it can take up to 24 hours to EQ a battery. I do not know if Midnite Solar new software will allow it, but set Bulk = Absorb = 2.4 volts. It would be ideal if you can monitor the SPG to get both the Voltage and Time worked out. Monitor SPG temp corrected until you get 100% SOC when it switches to float. Do not exceed 2.45 vpc.

              What you are really looking for is once you hit 100% SOC is no one cell is below 2.35 or above 2.45 when it switches to Float. 2.4 is the middle ground. It is all about trade-offs. At 2.35 vpc you get less capacity but longer cycle life. At 2.45 vpc you get maximum capacity but less cycle life. You have to decide between the two evils. If it were me I would choose the lessor of the two evils and lean toward 2.35 to get maximum battery life.
              MSEE, PE

              Comment


              • #8
                Yes, I am using a temp compensated hydro. Reading it is not the most intuitive thing in the world though and the scale seems rather large considering I'm trying to determine .01 or .02 differences from that stupid scale on the bulb. The trojan table is confusing, table 7 in the user's guide says that at 100% SOC the sg should be 1.277 but then lists the open circuit voltage per cell as 2.122

                I need to get a better hydro, like the digital one that trojan shows in the users guide maybe.
                Then you're saying to start an eq and then monitor the sg every hour until it either stops increasing or reaches 1.277?
                The midnite allows me to alter both the absorb charge time and voltage per cell. At present it is set to 2.35V per cell and a time of 4 hours, it was set to 3hrs until a couple of weeks ago when i changed it to 4 hrs. My float voltage is set to 52.8

                Belay my last, I just looked up that DMA 35 hydrometer...I ain't paying 2500 bones for that. What are my other options? My temp compensated one is an OTC, my non temp comp one is a Deka
                1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

                Comment


                • #9
                  Originally posted by thastinger View Post
                  I need to get a better hydro, like the digital one that trojan shows in the users guide maybe
                  Yes you need a better hydro, but Floaters are the most accurate to my knowledge. Let me look around for a decent priced lab quality hydro and I will get back to you.
                  MSEE, PE

                  Comment


                  • #10
                    Shop around and find a Durac Model # 50860.

                    Quick search truned up in Amazon

                    Google turns up this


                    MSEE, PE

                    Comment


                    • #11
                      Ok thanks.

                      Could you address the below please

                      Then you're saying to start an eq and then monitor the sg every hour until it either stops increasing or reaches 1.277?
                      The midnite allows me to alter both the absorb charge time and voltage per cell. At present it is set to 2.35V per cell and a time of 4 hours, it was set to 3hrs until a couple of weeks ago when i changed it to 4 hrs. My float voltage is set to 52.8
                      1150W, Midnite Classic 200, Cotek PSW, 8 T-605s

                      Comment


                      • #12
                        Originally posted by thastinger View Post

                        Then you're saying to start an eq and then monitor the sg every hour until it either stops increasing or reaches 1.277?
                        That is exactly how it is done. Although I think the SPG might be a little lower. Check with Trojan.
                        MSEE, PE

                        Comment


                        • #13
                          Another thought

                          Originally posted by Sunking View Post
                          That is exactly how it is done. Although I think the SPG might be a little lower. Check with Trojan.
                          Here ask this question on the form and let's see what they say.

                          I have a friend that was talking to one of the better battery companies. The
                          company is suggesting that if you have enough solar, it is better to do only
                          a float charge every day as long as you get to full charge. This is more
                          true for systems that average no more than a 70% DOD. Once a week do a
                          regular bulk charge to mix the electrolytes, followed by the normal float
                          charge. This is why Midnight recently put out an upgrade to their controller
                          so you could increase the days between bulk charging. Prior to the upgrade
                          the counter reset every night at midnight and the bulk charge would
                          automatically occur each day.

                          The same Battery company recommended only doing an EQ charge when needed and
                          that would seldom be needed more than 1-2 times a year.

                          What would be wrong with only a float charge every day and a bulk charge
                          once a week as long as you attained full charge every day. Would not the
                          higher voltage of a bulk harm the batteries more than float if it is not
                          needed?

                          Comment


                          • #14
                            Originally posted by Retreat12 View Post
                            Here ask this question on the form and let's see what they say.

                            I have a friend that was talking to one of the better battery companies. The
                            company is suggesting that if you have enough solar, it is better to do only
                            a float charge every day as long as you get to full charge.
                            Float charge is best but for the most part incompatible with solar for 2 reasons.:
                            • Panel wattage would have to be grossly over-sized.
                            • Not enough Sun Hours in a day.
                            MSEE, PE

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