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  • my cheapo off grid system

    had a pm requesting to know more about my off grid system so here are a couple of pics . DSCN8083[1].JPGDSCN8084[1].JPG

    the 7 panels i picked up used for $950au they are 250w each. so 1750w array, the 2 charge controllers are pwm 30amp $40au each off ebay 4 x 75ah marine batteries $700au 2 x 100ah deep cycle batteries $470au they are arranged in series, 2 banks of parallel with 2 marine and one deep cycle. the series banks are matched at 250ah 24v. 4 panels are in parallel to one charge controller the other 3 panels in parallel to the other charge controller. these are connected via 25amp cable at 10meters. 2 lengths at 10meters each to each charge controller. i get 20amps off the charge controller with the 4 panels and 15amps off the charge controller with the 3 panels. so about 35amps in total. so the battery bank is over paneled, i figure im losing about 600w through the cabling but still getting 1000w into the batteries which is plenty. the alternative would be a $1000 mppt charge controller to get 1700w but not worth the expense. could get another 7 panels for $1000 and more than 1700w with pwm charge controllers. the batteries never go below 75%soc and i run a fridge, washing machine ,coffee machine,computers, lights, tv, power tools. the inverter is a 24v 2000w for $360au. so total cost to set up was about $2500au. i know you should use the same batteries in a bank but i balanced the series banks. the parallel banks can be unmatched as the current still flows through the batteries in the parallel banks till they are all charged.

  • #2
    Originally posted by almac View Post
    had a pm requesting to know more about my off grid system so here are a couple of pics . [ATTACH]7327[/ATTACH][ATTACH]7328[/ATTACH]

    the 7 panels i picked up used for $950au they are 250w each. so 1750w array, the 2 charge controllers are pwm 30amp $40au each off ebay 4 x 75ah marine batteries $700au 2 x 100ah deep cycle batteries $470au they are arranged in series, 2 banks of parallel with 2 marine and one deep cycle. the series banks are matched at 250ah 24v. 4 panels are in parallel to one charge controller the other 3 panels in parallel to the other charge controller. these are connected via 25amp cable at 10meters. 2 lengths at 10meters each to each charge controller. i get 20amps off the charge controller with the 4 panels and 15amps off the charge controller with the 3 panels. so about 35amps in total. so the battery bank is over paneled, i figure im losing about 600w through the cabling but still getting 1000w into the batteries which is plenty. the alternative would be a $1000 mppt charge controller to get 1700w but not worth the expense. could get another 7 panels for $1000 and more than 1700w with pwm charge controllers. the batteries never go below 75%soc and i run a fridge, washing machine ,coffee machine,computers, lights, tv, power tools. the inverter is a 24v 2000w for $360au. so total cost to set up was about $2500au. i know you should use the same batteries in a bank but i balanced the series banks. the parallel banks can be unmatched as the current still flows through the batteries in the parallel banks till they are all charged.
    500Ah capacity would give you 6kWh total energy capacity so if you use only 25% of it nightly your total consumption is 1.5 kWh. Seems a little low to me unless you alternate those loads- today we have lights, tomorrow- computers and so on Fridge full of beer probably needs to run 24x7 . Just saying anyone trying to follow your setup should realize the energy budget they must to fit in: 1.5 kWh over 4 hrs of dark time is only 375W in average. Washing machine probably runs during day time otherwise I simply don't see how it all fits into 375W. I considered very ideal conditions, in reality it will be at least 10% less.

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    • #3
      Originally posted by max2k View Post
      500Ah capacity would give you 6kWh total energy capacity so if you use only 25% of it nightly your total consumption is 1.5 kWh. Seems a little low to me unless you alternate those loads- today we have lights, tomorrow- computers and so on Fridge full of beer probably needs to run 24x7 . Just saying anyone trying to follow your setup should realize the energy budget they must to fit in: 1.5 kWh over 4 hrs of dark time is only 375W in average. Washing machine probably runs during day time otherwise I simply don't see how it all fits into 375W. I considered very ideal conditions, in reality it will be at least 10% less.
      i use heavy loads daytime only. fridge (keep frozen water bottles in freezer)washing machine power tools during daytime. this doesnt drain the batteries at all. night time use light loads like lights, tv, laptops. this is from sundown,(5pm its winter) till about 10pm then i turn the inverter off till morning

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      • #4
        Originally posted by almac View Post
        i use heavy loads daytime only. fridge (keep frozen water bottles in freezer)washing machine power tools during daytime. this doesnt drain the batteries at all. night time use light loads like lights, tv, laptops. this is from sundown,(5pm its winter) till about 10pm then i turn the inverter off till morning
        Makes sense- 'off grid' still feels more like a lifestyle, we're spoiled with energy availability. BTW, 'power tools' might not drain too much power but you probably need them during daylight hours anyway.

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        • #5
          Originally posted by almac View Post
          had a pm requesting to know more about my off grid system so here are a couple of pics . [ATTACH]7327[/ATTACH][ATTACH]7328[/ATTACH]

          the 7 panels i picked up used for $950au they are 250w each. so 1750w array, the 2 charge controllers are pwm 30amp $40au each off ebay 4 x 75ah marine batteries $700au 2 x 100ah deep cycle batteries $470au they are arranged in series, 2 banks of parallel with 2 marine and one deep cycle. the series banks are matched at 250ah 24v. 4 panels are in parallel to one charge controller the other 3 panels in parallel to the other charge controller. these are connected via 25amp cable at 10meters. 2 lengths at 10meters each to each charge controller. i get 20amps off the charge controller with the 4 panels and 15amps off the charge controller with the 3 panels. so about 35amps in total. so the battery bank is over paneled, i figure im losing about 600w through the cabling but still getting 1000w into the batteries which is plenty. the alternative would be a $1000 mppt charge controller to get 1700w but not worth the expense. could get another 7 panels for $1000 and more than 1700w with pwm charge controllers. the batteries never go below 75%soc and i run a fridge, washing machine ,coffee machine,computers, lights, tv, power tools. the inverter is a 24v 2000w for $360au. so total cost to set up was about $2500au. i know you should use the same batteries in a bank but i balanced the series banks. the parallel banks can be unmatched as the current still flows through the batteries in the parallel banks till they are all charged.
          I am sure your system is working fine for you now. But I am willing to bet that some if not all of those batteries will die after a short life.

          When the do I would suggest that instead of replacing them with cheap ones of different sizes determine how big your system needs to be to cover your electric loads (if 500Ah is not enough) and build a battery system using all the same batteries wired for your 24volt inverter. And while it may seem too high an expense using a single MPPT CC to get full usage out of your 1750watt panel system will prove less expensive in the long run.

          Comment


          • #6
            Originally posted by SunEagle View Post
            I am sure your system is working fine for you now. But I am willing to bet that some if not all of those batteries will die after a short life.

            When the do I would suggest that instead of replacing them with cheap ones of different sizes determine how big your system needs to be to cover your electric loads (if 500Ah is not enough) and build a battery system using all the same batteries wired for your 24volt inverter. And while it may seem too high an expense using a single MPPT CC to get full usage out of your 1750watt panel system will prove less expensive in the long run.
            hi, thanks for your reply, the bank is actually 250ah. the series banks are balanced, all the batteries were full ycharged when configured, i monitor the sg daily. all batteries recharge 100%, none fall below 75% soc so how will they all have a shortened life?

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            • #7
              Originally posted by almac View Post
              hi, thanks for your reply, the bank is actually 250ah. the series banks are balanced, all the batteries were full ycharged when configured, i monitor the sg daily. all batteries recharge 100%, none fall below 75% soc so how will they all have a shortened life?
              Any time you wire batteries in parallel you run the chance of not getting a balanced charge or discharge. This can happen if there is just a slight difference in resistance on one set of battery terminal or wires.

              So you may think all of the batteries are getting the same charging current they are not. The more they get cycled the higher the difference if resistance becomes because now you are adding the battery plate resistance which is changing unequally.

              Keeping them at or above 75% SOC helps get more life out of them but two many paths for the charging current to follow ends up with unequally charged/discharged batteries.

              Oh. I just noticed in your pictures you have 2 x 75Ah + 1 x 100Ah battery making up the "bank". Beside the issue with parallel wiring, charging a battery bank made up from different sized (Ah) rated batteries will definitely cause unequal charge/discharge issues because the 75Ah should only get about 7.5amp charging and the 100Ah should get 10Amp charging. Your CC does not have the ability to send the correct amount of current to each battery so they all get the same charge current and the 75Ah will probably get too much or the 100Ah will get too little.
              Last edited by SunEagle; 07-23-2015, 03:48 PM. Reason: added last paragraph

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              • #8
                Originally posted by SunEagle View Post
                Any time you wire batteries in parallel you run the chance of not getting a balanced charge or discharge. This can happen if there is just a slight difference in resistance on one set of battery terminal or wires.

                So you may think all of the batteries are getting the same charging current they are not. The more they get cycled the higher the difference if resistance becomes because now you are adding the battery plate resistance which is changing unequally.

                Keeping them at or above 75% SOC helps get more life out of them but two many paths for the charging current to follow ends up with unequally charged/discharged batteries.

                Oh. I just noticed in your pictures you have 2 x 75Ah + 1 x 100Ah battery making up the "bank". Beside the issue with parallel wiring, charging a battery bank made up from different sized (Ah) rated batteries will definitely cause unequal charge/discharge issues because the 75Ah should only get about 7.5amp charging and the 100Ah should get 10Amp charging. Your CC does not have the ability to send the correct amount of current to each battery so they all get the same charge current and the 75Ah will probably get too much or the 100Ah will get too little.
                they will also discharge unequally, iv noticed the 75ah batteries discharge more than the 100ah, and the 100ah are the 1st to reach 100% soc. ok i will let this experiment run, see how long these batteries last.

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                • #9
                  Originally posted by almac View Post
                  they will also discharge unequally, iv noticed the 75ah batteries discharge more than the 100ah, and the 100ah are the 1st to reach 100% soc. ok i will let this experiment run, see how long these batteries last.
                  Glad you understand.

                  Learning about a solar battery system is fun but can get real expensive if you started out by purchasing some very expensive high end batteries that get turned into Boat Anker during a learning curve.

                  Comment


                  • #10
                    Originally posted by almac View Post
                    they will also discharge unequally, iv noticed the 75ah batteries discharge more than the 100ah, and the 100ah are the 1st to reach 100% soc. ok i will let this experiment run, see how long these batteries last.
                    your parallel sub-bank has 150Ah capacity and it's different type of battery from 100Ah battery in series. Can you rearrange them in this way: 2x75 - 2x75 giving you the same 24V but 150Ah and 1x100-1x100 bank? This would make much more uniform arrangement from charging / discharging point of view. This would also better fit your asymmetric charging source: currently you have 4/1 & 3/1 arrangement feeding banks of equal capacity. In the new arrangement it would be 4/1.5 & 3/1- you'll utilize your 4 panel bank of solar panels better. Ideally you'd want 4.5/1.5 but it's hard to get half panel .

                    When charging parallel cells I think they auto- balance as more charged cell produces higher voltage reducing automatically amount of charge going to that cell from the total current supplied by the controller. Cells connected in series is a different matter and they can go out of balance with time as the very same charging/discharging current goes through them so over many cycles you can accumulate big enough difference. The 'auto- balancing' would also happen here when fully charged cell would start breaking water while less charged cell will still be taking in charge from the same current but it is definitely not good for 'boiling' cell. Your 100Ah battery seems to suffer from this as it takes 1.5 times less charge to 'fill it up' compare to its partner in series.

                    Comment


                    • #11
                      Originally posted by max2k View Post
                      your parallel sub-bank has 150Ah capacity and it's different type of battery from 100Ah battery in series. Can you rearrange them in this way: 2x75 - 2x75 giving you the same 24V but 150Ah and 1x100-1x100 bank? This would make much more uniform arrangement from charging / discharging point of view. This would also better fit your asymmetric charging source: currently you have 4/1 & 3/1 arrangement feeding banks of equal capacity. In the new arrangement it would be 4/1.5 & 3/1- you'll utilize your 4 panel bank of solar panels better. Ideally you'd want 4.5/1.5 but it's hard to get half panel .

                      When charging parallel cells I think they auto- balance as more charged cell produces higher voltage reducing automatically amount of charge going to that cell from the total current supplied by the controller. Cells connected in series is a different matter and they can go out of balance with time as the very same charging/discharging current goes through them so over many cycles you can accumulate big enough difference. The 'auto- balancing' would also happen here when fully charged cell would start breaking water while less charged cell will still be taking in charge from the same current but it is definitely not good for 'boiling' cell. Your 100Ah battery seems to suffer from this as it takes 1.5 times less charge to 'fill it up' compare to its partner in series.
                      ok, so i would have 2 banks in series. 2 x 75 -2 x 75 and 1 x 100-1 x 100 on separate charge controllers. so would i draw on these separate banks separately? or can i put these 2 series banks in parallel.

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                      • #12
                        Originally posted by almac View Post
                        ok, so i would have 2 banks in series. 2 x 75 -2 x 75 and 1 x 100-1 x 100 on separate charge controllers. so would i draw on these separate banks separately? or can i put these 2 series banks in parallel.
                        Probably the best arrangement with your current battery system is to put the 4 x 75Ah in one system (2 in series and 2 set in parallel) which will get you a 24volt 150Ah system. Then put the 2 100Ah batteries in series to yield a 24volt 100Ah system.

                        To determine the best arrangement of your panels and charge controllers please provide their specs again. Ultimately you want to get about 15amps of charging going into the 4 x75Ah system and 10Amps into teh 100Ah system.

                        I would get a second inverter and use one for each battery system. Putting both battery systems in parallel to one inverter will result in uneven discharging.

                        Comment


                        • #13
                          Originally posted by SunEagle View Post
                          Probably the best arrangement with your current battery system is to put the 4 x 75Ah in one system (2 in series and 2 set in parallel) which will get you a 24volt 150Ah system. Then put the 2 100Ah batteries in series to yield a 24volt 100Ah system.

                          To determine the best arrangement of your panels and charge controllers please provide their specs again. Ultimately you want to get about 15amps of charging going into the 4 x75Ah system and 10Amps into teh 100Ah system.

                          I would get a second inverter and use one for each battery system. Putting both battery systems in parallel to one inverter will result in uneven discharging.
                          have reconfigured batteries as you suggested. the panel specs are 36v 250w. i get 20amps out of the charge controller with the 4 panels , and 15amps out of the charge controller with the 3 panels. thanks for your help you have saved my batteries, much appreciated

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                          • #14
                            Originally posted by almac View Post
                            have reconfigured batteries as you suggested. the panel specs are 36v 250w. i get 20amps out of the charge controller with the 4 panels , and 15amps out of the charge controller with the 3 panels. thanks for your help you have saved my batteries, much appreciated
                            Well I haven't saved them but hopefully I got your attention and you now have a better understanding concerning solar/battery systems.

                            You might be putting too much into both battery systems. 20amps charging the 150Ah bank is a little high for FLA as well as 15amps into the 100Ah system. If those batteries are AGM you might be ok but I am not sure.

                            To be safe maybe disconnecting 1 panel of the 4 panels on the 150Ah system and 1 of the 3 panels on the 100Ah system will get you closer to that C/10 ratio. I know that you now have a couple of extra panels but see how your battery systems work on the lower number.

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                            • #15
                              Originally posted by almac View Post
                              the alternative would be a $1000 mppt charge controller to get 1700w but not worth the expense.

                              Huh? Couldn't you get one for like half that
                              Outback Flexmax 80 MPPT Solar Charge Controller

                              or use 2 40A mppt controllers for just over $400
                              Renogy 40 Amp MPPT Solar Charge Controller

                              Mod note. It's fine to post the name of gear, but not links to competing vendors. The
                              funds to pay the hosting fees and electric bill come from equipment sales from
                              http://www.solarreviews.com/ They are low pressure sales, but still appreciate the chance to make a sale.
                              Last edited by Mike90250; 07-24-2015, 06:58 PM. Reason: remove links

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