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  • Battery Configuration

    I am just learning and read a couple of books, but still plenty of questions. I have 400 watts on the roof, sun all day and two new 200 amp 6 volt deep cycle batteries giving me an output of 12 volts. How would I put more batteries in the mix to maximize the system with 12 volts or should I go 24 volts (even though I may not use all the electricity with my led lights. Like I said just trying to maximize it )

    Thanks

  • #2
    What is the make and model of your charge controller? Based on what is the type and max input values will help determining how you may be able to enlarge your system.

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    • #3
      For the size of system that you are starting with 12 volts would be fine. However, if you plan on expanding later you may find 24 volts more practical. If you start with a 24 volt system you will avoid having to buy new 24 volt gear to replace the 12 volt.

      A note on led lights. Decent 12 volt led lights are inexpensive and plentiful. I have had good success with running them as pairs in series to accommodate the 24 volt system in my RV.
      Last edited by PNW_Steve; 09-19-2019, 05:31 PM.

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      • #4
        Originally posted by SunEagle View Post
        What is the make and model of your charge controller? Based on what is the type and max input values will help determining how you may be able to enlarge your system.
        It is a MPPT SOLAR charge controller 12/24 volts, 60 amps and max watts is 750

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        • #5
          Originally posted by PNW_Steve View Post
          For the size of system that you are starting with 12 volts would be fine. However, if you plan on expanding later you may find 24 volts more practical. If you start with a 24 volt system you will avoid having to buy new 24 volt gear to replace the 12 volt.

          A note on led lights. Decent 12 volt led lights are inexpensive and plentiful. I have had good success with running them as pairs in series to accommodate the 24 volt system in my RV.
          It looks like I am going to have to run an inverter. Originally I wanted to switch my driveway lights to 12 volts and hook up the 12 v dc to the existing 120 volt wires with a load of about 3 or 4 watts for each pole light as you come up the driveway (total 16 watts led), but the run is about 200 feet and with 12 wire I believe that would not support the current for that long a run ??

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          • #6
            Originally posted by dinows View Post

            It is a MPPT SOLAR charge controller 12/24 volts, 60 amps and max watts is 750
            Well 400 watts is a little light to charge a 400Ah 12V battery system. You should be generating about 40 amps which would be 480 watts. With that CC you can go up to 750 watts so adding a third 200watt panel will help. but adding another 400 watts might exceed the CC input rating.

            My guess is you are limited with your input wattage if you stay with a 12v system. Going to 24v will allow you to enlarge it without needing a new CC.

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            • #7
              Originally posted by SunEagle View Post

              Well 400 watts is a little light to charge a 400Ah 12V battery system. You should be generating about 40 amps which would be 480 watts. With that CC you can go up to 750 watts so adding a third 200watt panel will help. but adding another 400 watts might exceed the CC input rating.

              My guess is you are limited with your input wattage if you stay with a 12v system. Going to 24v will allow you to enlarge it without needing a new CC.
              So you think i should stay with the 2 , 200 amp 6 volt batteries

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              • #8
                Originally posted by dinows View Post

                So you think i should stay with the 2 , 200 amp 6 volt batteries
                Sorry. I thought your batteries were 200Ah at 12v. If you only have a 200Ah bank using 2 x 6v then you have more then enough solar panel wattage. Actually you may have too much depending on the amount of charging amps you get during the day.

                Basically you want to have about a C/10 charge rate where C = the Amp Hour rating of your battery system. So with a 200Ah system you would need 20 amps to meet the C/10 charge rate. So right now you have more than enough panel wattage at 400 to get that 20 amps or more.

                Depending on what you need for a daily watt hour use should determine how big a battery system you have. With a 12V 200Ah you can safely generate about 600 watt hours a day.

                If you need a bigger battery system then you need to match it with charging amps to meet that C/10 charge rate.

                Comment


                • #9
                  Originally posted by dinows View Post

                  It looks like I am going to have to run an inverter. Originally I wanted to switch my driveway lights to 12 volts and hook up the 12 v dc to the existing 120 volt wires with a load of about 3 or 4 watts for each pole light as you come up the driveway (total 16 watts led), but the run is about 200 feet and with 12 wire I believe that would not support the current for that long a run ??
                  I would recommend calculating your wire size and voltage drop instead of assuming that it won't work. Here is a handy calculator: https://www.wirebarn.com/Wire-Calculator-_ep_41.html

                  looks to me like the 12gauge would work IF you can tolerate a voltage drop approaching 5%.

                  Edit: I goofed. I used 250' instead of 200'. Looks to me like you have a good shot at running straight DC and being able to use existing wire.
                  Last edited by PNW_Steve; 09-22-2019, 04:25 PM.

                  Comment


                  • #10
                    Originally posted by PNW_Steve View Post

                    I would recommend calculating your wire size and voltage drop instead of assuming that it won't work. Here is a handy calculator: https://www.wirebarn.com/Wire-Calculator-_ep_41.html

                    looks to me like the 12gauge would work IF you can tolerate a voltage drop approaching 5%.

                    Edit: I goofed. I used 250' instead of 200'. Looks to me like you have a good shot at running straight DC and being able to use existing wire.
                    OK Thanks, what the heck, might as well give it a try !!

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                    • #11
                      One more thing, would I get more bang for my buck by hooking this up with 12 volts or using an inverter and running the 120 volts Thanks

                      Comment


                      • #12
                        Originally posted by SunEagle View Post

                        Sorry. I thought your batteries were 200Ah at 12v. If you only have a 200Ah bank using 2 x 6v then you have more then enough solar panel wattage. Actually you may have too much depending on the amount of charging amps you get during the day.

                        Basically you want to have about a C/10 charge rate where C = the Amp Hour rating of your battery system. So with a 200Ah system you would need 20 amps to meet the C/10 charge rate. So right now you have more than enough panel wattage at 400 to get that 20 amps or more.

                        Depending on what you need for a daily watt hour use should determine how big a battery system you have. With a 12V 200Ah you can safely generate about 600 watt hours a day.

                        If you need a bigger battery system then you need to match it with charging amps to meet that C/10 charge rate.
                        Just to clarify, each 6 volt battery is 200 (total 400) is that how you figured it Thanks
                        )

                        Comment


                        • #13
                          Originally posted by dinows View Post

                          Just to clarify, each 6 volt battery is 200 (total 400) is that how you figured it Thanks
                          )
                          My original answer to your post was removed when the Server was reformatted.

                          Actually when you wire batteries in series you add up the voltage but the total Ah is the same as one. Your system of 2 x 6V 200Ah batteries wired in series would become a 12V 200Ah system.

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                          • #14
                            Originally posted by SunEagle View Post

                            My original answer to your post was removed when the Server was reformatted.

                            Actually when you wire batteries in series you add up the voltage but the total Ah is the same as one. Your system of 2 x 6V 200Ah batteries wired in series would become a 12V 200Ah system.
                            OK Thanks for the help but according to "Sun Eagle" with my 400 watts of panels I may have "to much" power going to the batteries, would you suggest additional batteries ? Thanks

                            Comment


                            • #15
                              Originally posted by dinows View Post

                              OK Thanks for the help but according to "Sun Eagle" with my 400 watts of panels I may have "to much" power going to the batteries, would you suggest additional batteries ? Thanks
                              You may have too much charging amps for that battery system IF all of the panels are facing due South and producing nameplate amps. Your batteries should be able to handle a C/8 charge rate which would be about 25 amps but if you get more you could cook the batteries with a C/7 or C/6 charge rate.

                              If you can measure the charging amps it would help determine if you have too much panel wattage but in most cases panels will never produce their name plate info.

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