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  • Number of solar panels to charge 6V 925 AH battery

    First post. I hope I won't break any forum rules.

    I'm looking to purchase this battery https://www.altestore.com/store/deep...battery-p9704/

    How many 340 watt mono solar panels do I need to charge the battery in 8 hrs? Assuming a 50% DoD.

    The other thing not clear to me is that the solar panel is 12V, while the battery is 6V. Does that matter? Is there any impact on efficiency?

    TIA.

  • #2
    That is quite a battery there. Just to be clear, you wish to charge one of these all by itself?

    Also, do you mean daylight hours, or sun-hours?

    Comment


    • #3
      Whoa partner. A single 6V battery is not going to do much. Your selection of useful charge controllers is -non existent-

      If you had 2 batteries, then you could use a 12V MPPT controller and make life easy

      925 / 2 = 460 ah x 6v = 2760 watt hours Winter day, assume only 3.5 usable solar hours, means you need a harvest of about 800 watts, or about a 1,000 watt PV array and 90A of charge controller. You have to split the array to 2, 500W arrays, each with a 60A controller..
      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


      • #4
        Originally posted by Mike90250 View Post
        [...] 925 / 2 = 460 ah [...]
        Why did you divide 925 by 2?

        Comment


        • #5
          Originally posted by azroute66 View Post
          why did you divide 925 by 2?
          50% dod.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

          Comment


          • #6
            @AzRoute66

            >> you wish to charge one of these all by itself?
            Yes.

            >> Also, do you mean daylight hours, or sun-hours?
            Sun-hours.

            Comment


            • #7
              @Mike90250

              >> A single 6V battery is not going to do much.
              The use case is for a 14-room student dorm with the following devices...
              1. Clock radio = 1W
              2. Phone Charger = 4W
              3. LED Light Bulb = 8W
              4. Table Fan = 10W

              Total: 23W.

              For 14 dorm rooms = 23 x 14 = 322W.
              With a 6V battery, the current draw is 322/6 = 53.7 amps.

              The battery supplies 460Ah (i.e. 50% dod),
              So from a 100% charge, number of hours before 50% discharge = 460/53.7 = 8.5 hours.

              Is my calculation accurate?


              >> Your selection of useful charge controllers is -non existent-
              I'm looking to get one that combines charger/inverter/transfer switch/equalization in one unit. E.g. http://www.tbbpower.com/eproductdeta...x?pdid=LN00481

              Assuming a 12V charge controller. Would the charger be able to reduce the 12V coming coming from the panels down to 6V that the battery needs? Or would this be inefficient?

              I apologize if these are novice, or naive questions. I don't know, that is why I ask.

              So going back to my OP, how many 340 watt mono solar panels do I need to charge the battery in 8 solar-hrs? Assuming a 50% DoD.

              Your answer was:
              >> you need a harvest of about 800 watts, or about a 1,000 watt PV array

              That means I need 3 of those 340W solar panes?

              Comment


              • #8
                Originally posted by fw12 View Post
                @Mike90250

                >> A single 6V battery is not going to do much.
                The use case is for a 14-room student dorm with the following devices...
                1. Clock radio = 1W
                2. Phone Charger = 4W
                3. LED Light Bulb = 8W
                4. Table Fan = 10W

                Total: 23W.

                For 14 dorm rooms = 23 x 14 = 322W.
                With a 6V battery, the current draw is 322/6 = 53.7 amps.

                The battery supplies 460Ah (i.e. 50% dod),
                So from a 100% charge, number of hours before 50% discharge = 460/53.7 = 8.5 hours.

                Is my calculation accurate?


                >> Your selection of useful charge controllers is -non existent-
                I'm looking to get one that combines charger/inverter/transfer switch/equalization in one unit. E.g. http://www.tbbpower.com/eproductdeta...x?pdid=LN00481

                Assuming a 12V charge controller. Would the charger be able to reduce the 12V coming coming from the panels down to 6V that the battery needs? Or would this be inefficient?

                I apologize if these are novice, or naive questions. I don't know, that is why I ask.

                So going back to my OP, how many 340 watt mono solar panels do I need to charge the battery in 8 solar-hrs? Assuming a 50% DoD.

                Your answer was:
                >> you need a harvest of about 800 watts, or about a 1,000 watt PV array

                That means I need 3 of those 340W solar panes?
                There are very very few solar charge controllers that are designed for a 6 volt battery.

                You might think about going with 2 x 6v 460Ah batteries wired in series to get a 12v bank at 460Ah which should be able to provide at least 2500watt hours a day assuming a 50% DOD.

                Although going to 50% DOD will shorten the life of any FLA type battery. Going to 20% to 25% DOD will probably get you the longest life.

                Once you determine the final battery voltage you will be able to determine the amount of panel wattage to charge it.

                Also very few places on earth will get 8 usable sun charging hours.
                Last edited by SunEagle; 11-14-2017, 12:25 PM. Reason: added last sentence

                Comment


                • #9
                  Mike90250 , of course, thank you.

                  Originally posted by fw12 View Post
                  [...] >> A single 6V battery is not going to do much.
                  The use case is for a 14-room student dorm with the following devices...
                  1. Clock radio = 1W
                  2. Phone Charger = 4W
                  3. LED Light Bulb = 8W
                  4. Table Fan = 10W

                  Total: 23W.

                  For 14 dorm rooms = 23 x 14 = 322W.
                  With a 6V battery, the current draw is 322/6 = 53.7 amps.

                  The battery supplies 460Ah (i.e. 50% dod),
                  So from a 100% charge, number of hours before 50% discharge = 460/53.7 = 8.5 hours.
                  So, now you want to do something with this battery. That is different. Listen to Mike, "A single 6V battery is not going to do much." Additionally, I don't think some of the items in your load list exist such as the 4W phone charger or 1W clock radio, but that part of the problem is trivial.

                  >> Your selection of useful charge controllers is -non existent-
                  I'm looking to get one that combines charger/inverter/transfer switch/equalization in one unit. E.g. http://www.tbbpower.com/eproductdeta...x?pdid=LN00481
                  The unit you specified does not support 6V, as Mike pointed out, the 6V charge controller (or inverter) just doesn't exist. That family of inverters supports either 24 or 48 V operation.

                  Assuming a 12V charge controller. Would the charger be able to reduce the 12V coming coming from the panels down to 6V that the battery needs? Or would this be inefficient?
                  Again, the 6V charge controller you seek doesn't exist, therefore it should not be assumed. Also, no useful panel puts out 12V, not even a '12 V panel'. The 340W panels you suggested will put out much more.

                  I apologize if these are novice, or naive questions. I don't know, that is why I ask.
                  Fine, but we are not used to quite this level of naivety. Don't start by picking a battery. Refine your load list then pick an inverter, make sure to add the inverter load/overhead to the load list. This inverter will support either 12, 24, or 48V systems. The inverter family you mentioned supports either 24V or 48V operation. Come back with an inverter, and the rest will be much easier.

                  Comment


                  • #10
                    You list the watts but not the volts of your appliances. Are they all 6v?

                    And I'm curious, why you would buy a single 6v battery for over $1300 when u could buy 4 L16H-ac batteries for the same money and be at 24v. Yes lower amp hours, but ok, buy 8 and run them 2 parallel banks of 4 batteries each bank in series. Even with 8 you'd still be almost half the cost of 4 of the batteries u linked.
                    285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

                    Comment


                    • #11

                      >> You might think about going with 2 x 6v 460Ah batteries wired in series to get a 12v bank
                      >> at 460Ah which should be able to provide at least 2500watt hours a day assuming a 50% DOD.

                      I considered that before. But doing so would take me over budget.

                      >> Additionally, I don't think some of the items in your load list exist such as the 4W phone charger or 1W clock radio.

                      They do exist, and we have them already.
                      http://energyusecalculator.com/elect...alarmclock.htm
                      http://energyusecalculator.com/elect..._cellphone.htm

                      >> the 6V charge controller you seek doesn't exist, therefore it should not be assumed
                      I could not find MPPT, but here is PWM. It's only 10A though.
                      https://www.cuttingedgepower.com/pro...rge-controller

                      >> You list the watts but not the volts of your appliances. Are they all 6v?
                      Devices are AC, not DC.

                      >> going to 50% DOD will shorten the life of any FLA type battery. Going to 20% to 25% DOD will probably get you the longest life.

                      I agree. My calculations are just on paper. In reality, I don't expect all devices to be in use in all rooms simultaneously. So the chances are good that it can stay below 30% DOD.

                      >> And I'm curious, why you would buy a single 6v battery for over $1300 when u could buy 4 L16H-ac batteries for the same money and be at 24v.

                      I'll take a look at your suggestion. I was looking at the IND17-6V battery because it is industrial grade, with 17 year lifespan, and 10 year warranty.

                      Cyclic Use: 30% DOD - 4000 cycles
                      Cyclic Use: 50% DOD - 2800 cycles

                      I looked up Trojan L16H-AC, and it says it has 1,200 CYCLES @ 50% DOD, and 1 year warranty. You can see the difference.

                      >> Yes lower amp hours, but ok, buy 8 and run them 2 parallel banks of 4 batteries each bank in series.

                      There is budget constraint.

                      Anyway, thank you all for the answers. I have gained more insight on what direction to follow.

                      Comment


                      • #12
                        1) forget the 6 volt system, no charge controllers and no inverters.

                        2) first pass, use the cheap batteries, 4 golf cart batteries, wired series/parallel for 12V 380ah If you have made any miscalculations, you only fried $400 worth of batteries

                        3) Look for a quality 12V 800W inverter, with low losses
                        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


                        • #13
                          After following your advice, here is what I came up with...

                          PANELS:
                          4 x 300W wired in parallel (=12V, 35Amp). I am assuming each panel puts out 8.5A.

                          BATTS:
                          Trojan solar AGM 6v 315ah
                          2 x 6V in series (=12V, 315Ah).

                          CONTROLLER:
                          2200W 12v Solar Inverter/charge controller 45A
                          This is a Inverter/charge controller/charger combo.

                          I have a couple of questions.

                          Q1. The charge controller says input voltage is 12V. Assuming I end up getting 24V panels instead of 12V, would this controller still work with it? I get confused when people start talking about nominal voltage, Vmp, Voc, etc. Which one should be looked at as input for the charge controller?

                          Q2. Will 4*300W panels charge my 2 batteries? Assuming 5 sun hours per day, and 30-50% DoD.

                          TIA.

                          Comment


                          • #14
                            Originally posted by fw12 View Post
                            After following your advice, here is what I came up with...

                            PANELS:
                            4 x 300W wired in parallel (=12V, 35Amp). I am assuming each panel puts out 8.5A.

                            BATTS:
                            Trojan solar AGM 6v 315ah
                            2 x 6V in series (=12V, 315Ah).

                            CONTROLLER:
                            2200W 12v Solar Inverter/charge controller 45A
                            This is a Inverter/charge controller/charger combo.

                            I have a couple of questions.

                            Q1. The charge controller says input voltage is 12V. Assuming I end up getting 24V panels instead of 12V, would this controller still work with it? I get confused when people start talking about nominal voltage, Vmp, Voc, etc. Which one should be looked at as input for the charge controller?

                            Q2. Will 4*300W panels charge my 2 batteries? Assuming 5 sun hours per day, and 30-50% DoD.

                            TIA.
                            WTF over?

                            For a 1200 watt panel with a MPPT controller takes 100 amps. How did you come up with 45 amps. Throw two of your panels away because they are not being used. Secondly 100 amps into a 300 AH battery is asking for smoke.
                            MSEE, PE

                            Comment


                            • #15
                              OK I have a little more time to help. OK you have a pair of Trojans SAGM 6 315's. So lets keep it there and take a look at the Spec Sheet. Batteries have a max charge rate they will accept. Trying to go faster than max recommended rate will not shorten the time it takes to saturate the battery. All it does is get you to Absorb phase faster at a lower state of state of charge. That means you will spend a lot more time in Absorb phase. Right there in great big print max rate is 20% of the 20 hour rate aka C/5. Where C = the battery capacity in Amp Hours (315 AH for this battery), and the number is charge rate in hours or 20% = 5 hours aka C/5.

                              What that is telling you the maximum charge rate is 315 AH / 5 H = 63 Amps. That does not mean you should charge at 63 amps, it just means go no faster the 63 amps. Think of it like a speed limit on the roads. Unlike man made laws which can be easily violated with no consequences, the Laws of Physics will be obeyed or instant consequences will follow. Things like explosions, fire, melted metal and acid spewing about.

                              How much panel wattage is that? Real simple answer and 5th grade math like above. First the battery voltage must be known which we already know to be 12 volts. Assuming you use a MPPT Controler Watts = Battery Voltage x Amps. So 12 volts x 63 amps = 756 watts. Lets just say 800 watts maximum on your battery. Using that same simple math we can re-write the formula real easily for Amps = Panel Wattage / Battery Voltage, or 1200 watts / 12 volts = 100 amps. Do you see a problem?

                              On to your next question is again simple 5th grade math. You have a 315 AH battery and if at 50% capacity is 315/ 2 = 157.5 AH. To replace 157.5 AH we have to supply the battery with 120%, or 1.2 x 157.5 = 189 AH or just say 190 AH. Can that be done in a day? Maybe, depends on how fast the battery can charge and HOW MANY SUN HOURS you have in a day. So lets say you have a 3 Sun Hour day in Winter. How many amps is that? Amps = Amp Hours / Hours, or 190 AH / 3 Hours = 63 Amps. Wow that just happens to be exactly the max charge rate your batteries can handle. In Summer is no problem because because you wil have 5 to 6 Sun Hours, so you have a lot of power that will not be used.

                              You need an 800 watt panel with a 65 Amp Charge Controller. Easy peazy math.

                              MSEE, PE

                              Comment

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