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  • Battery bank charging WAY slower after modification.

    Hi folks, need help!
    I’m 3yrs now on my solar project, been upgrading, learning and modifying along the way trying to get the best out of what I got.. The goal started as an emergency power source but now working towards running the whole house minus my Hvac unit. I got one that’s got me stumped now. So here is the setup and status before the last mod I did:
    1) I had five 100 watt panels in parallel. At a distance, give or take, of 100’-120’ from the battery bank.
    2) Off brand 40amp controller.
    3) 3500 watt pure sine inverter
    4) Seven UB121000 100ah batteries, in parallel = 700ah bank.
    All tests to date have only been conducted during the day while charging was available. How did it perform? Not too bad I guess? My bank capacity would level around 60-70%, depending on power consumption of course, then towards late afternoon after say 6-7 hours of use it would start dropping towards the 50% range even though the sun was still plentiful. I noticed I was only getting a small percentage of charging current coming in so I started looking into my next mod/upgrade to see how I could gain efficiency?
    Modification:
    1) Renogy River 40amp controller.
    2) I added one more panel to the array for 3 groups of 2 and wired them in series/parallel for a 24v array. One thought here was maybe with that distance I had going the higher voltage would provide a better push to the bank?
    3) Added 1 more battery. End goal for the design is 10 batteries for a 1000ah bank. I’m now at 8.
    First test. How did it do? Awesome! Under the same conditions the bank capacity stayed between 70-80%. One thing that confused me though was At times that sucker had a charge current coming in at 25amps, even hit 30amps at one point. I didn’t understand cause if I wired each group of 2 panels in series (24v/5.5a) and then the 3 groups in parallel (24v/16.5a) then how the heck was I getting such a high current coming in? The current was reading almost as if I still had All panels in parallel? Didn’t complain though cause with that current I was rocking and rolling. So that is my first question right there? How did that happen?
    Now here’s my problem!
    after that test I shut it down and switched back over to the grid an 2 days later my battery bank is still not fully charged? Hell it was charging better while under a load? Controller is reading a charge coming in.. but it’s charging super super slow now. Never had that problem even when the panels were set up for 12v.. when not in use the bank always charged up pretty quick. I understand the bigger the bank gets it will take longer to charge but geez shouldn’t take that long right? I’m sure I got something out of sorts somewhere? The parameters seem to be set normal on the controller however I am confused on setting it 12v, 24v, or 12v/24v now that I got a 24v array and a 12v bank. My understanding was that the Renogy Rover automatically distinguished the voltage coming in and charged the bank accordingly?
    Long ass question, sorry y’all.. Yupp, I’m “that” guy. Any words of wisdom will be much appreciated! Thanks.. ✌️

  • #2
    I see a number of issues with your system.

    1. if you do not have an MPPT type charge controller you are really only getting 67% of your total panel wattage to charge the batteries.
    2. parallel wired batteries tend to charge and discharge unevenly so IMO one or more are starting to fail. On top of that you need about 1/10 the Ah rating of your battery system to properly charge them. So with the existing system of 700Ah that would be 70 amps but you are getting only 40amps max with that CC. Going to more batteries will only hurt you unless you increase the charge controller size and type to accommodate proper charging.
    3. that 3500watt inverter can draw close to 300amps at 12volts so IMO it is too big for your system.

    You really need to balance your system so that you have the right amount of panel wattage providing a C/8 to C/12 charge rate to your batteries. Also anytime you wire panels or batteries in parallel you end up with a system ready for failure. Increasing the size will do nothing unless it is done properly.

    Comment


    • #3
      There is so much wrong here, not sure where to start. Basically you have done everything wrong and you are stuck inside a 12 volt toy box. So I am not even going to try to help, you have a fire bomb waiting to explode.

      However there is one thing I can say for sure. You have more money that you know what to do with except throw it away. I say this because I know anything you take off-grid is going to cost you 5 to 10 times more than the Power Company will charge you for the rest of your life. If you think you are doing the world a favor, think again you just became a heavy polluter and loosing money fast. Good luck with that.

      Give you a clue where you went wrong. Using very expensive low power 12 volt panels, and using a PRIME NUMBER of panels. Another clue, never ever parallel batteries .
      Last edited by Sunking; 06-02-2020, 11:32 AM.
      MSEE, PE

      Comment


      • #4
        Ok, so good stuff here. Obviously I started into this as an amateur and haven’t had the benefit of speaking with knowledgeable and experienced people. So, the controller I have is in fact a MPPT, however I understand now from what your saying it is rated to low for the bank size I got, on top of having an inverter that is potentially sucking it down. Did I understand that correct? So Question.. even if I’m only pulling a load of 10 or 15amps AC.. will the inverter still pull those high DC amps (300) off my batteries? I’m an I&E guy so I got some knowledge but the DC world is new to me and throws curves balls at me.. I did notice that issues were starting up as I was adding more batteries but It seems now I was thinking backwards about it lol. I most likely will only be needing to run about 10amps ac, but would like a set up for 15. In your opinion, with my set up where would you start?

        one idea I originally had was making to small banks That I could toggle between instead of one big one? If I made 2 banks of 4 batteries (400ah each) my 40amp controller would be sufficient then yea? Leaving me to deal with the inverter issue? throwing a lot out, sorry man.. you’re the first person I’ve talked to since I started this project 3yrs ago

        Comment


        • #5
          Originally posted by Iss_shaffer View Post
          Ok, so good stuff here. Obviously I started into this as an amateur and haven’t had the benefit of speaking with knowledgeable and experienced people. So, the controller I have is in fact a MPPT, however I understand now from what your saying it is rated to low for the bank size I got, on top of having an inverter that is potentially sucking it down. Did I understand that correct? So Question.. even if I’m only pulling a load of 10 or 15amps AC.. will the inverter still pull those high DC amps (300) off my batteries? I’m an I&E guy so I got some knowledge but the DC world is new to me and throws curves balls at me.. I did notice that issues were starting up as I was adding more batteries but It seems now I was thinking backwards about it lol. I most likely will only be needing to run about 10amps ac, but would like a set up for 15. In your opinion, with my set up where would you start?

          one idea I originally had was making to small banks That I could toggle between instead of one big one? If I made 2 banks of 4 batteries (400ah each) my 40amp controller would be sufficient then yea? Leaving me to deal with the inverter issue? throwing a lot out, sorry man.. you’re the first person I’ve talked to since I started this project 3yrs ago
          Well one question I have is how many watt hours do you plan on using each day? That will start you on your design of a solar/battery system.

          Next if you need a lot of watt hours then you may want to look into low voltage/high Amp Hour rated batteries.

          Next if you really need a big system then get out of using 12volts. Look into a 24V or 48V battery system.

          Finally a large watt rated inverter will draw up to 10% of its rating just being turned on. So while you may never use the full potential of 3500watt you have added a significant load to your battery system.

          Now based on your watt hour needs you should be able to build your balanced system instead of cobbling together a couple of smaller ones that more than likely will not work and end up having dead batteries.

          Comment


          • #6
            SunKing,

            ok, so I’m over the part where you made me feel like a jackass. I’m just a guy who has bought a little piece at a time. And I came to this forum to get help from people like yourself, not only to gain knowledge, and a more efficient setup, but a safe one as well. If my post gave you the idea that I’m some little rich boy with nothing better to do with my money than to throw it away then that is a great misunderstanding. I’ve never joined a forum before. I thought it was a place where folks looking for help get help? So with that being said brother... I know you said you weren’t gonna help me but I need all I can get man.. And what I got to work with is what I got and it is what it is cause I don’t have money to throw away. So... I do have an even number of panels now (6). Wired in series and parallel.. with the 40amp controller would down sizing my bank from 8 to 4 batteries be a step in the right direction? And also is it possible to set it up with 2 separate banks? Like a truck with 2 gas tanks, or is that line of thinking wrong? If I gotta downsize my inverter should I go 24v and put my batteries in series? You said I got a bomb, hell help me out please man? Seriously.
            thanks ✌️
            Last edited by Iss_shaffer; 06-02-2020, 01:59 PM.

            Comment


            • #7
              SunEagle,

              yea I’m an idiot.. please forgive And bare with me. I never calculated any watt hours. Like I said this all started as a little emergency generator project, like I just wanted to run a fridge and a couple of lights maybe. Then I got more into it and just started going with it. My time is always spread so thin and my research sometimes suffers because of that. But sounds like I need to take a step back and figure out what my energy needs are. Do you know any good and reliable websites where I can learn the formulas I need to get those answers? I got a lot invested now after 3yrs and desperately want to get it right.
              So in efforts to salvage what I got... if I go 24v, which my panels are now configured for.. and I buy a 24v inverter at the proper wattage that suits my energy needs... could I group the 8 batteries in 4 groups of 2, series & parallel (making it a 24v/400ah bank right?) and still be good with the 40amp MPPT controller?
              I appreciate your time ✌️

              Comment


              • #8
                Originally posted by Iss_shaffer View Post
                SunEagle,

                yea I’m an idiot.. please forgive And bare with me. I never calculated any watt hours. Like I said this all started as a little emergency generator project, like I just wanted to run a fridge and a couple of lights maybe. Then I got more into it and just started going with it. My time is always spread so thin and my research sometimes suffers because of that. But sounds like I need to take a step back and figure out what my energy needs are. Do you know any good and reliable websites where I can learn the formulas I need to get those answers? I got a lot invested now after 3yrs and desperately want to get it right.
                So in efforts to salvage what I got... if I go 24v, which my panels are now configured for.. and I buy a 24v inverter at the proper wattage that suits my energy needs... could I group the 8 batteries in 4 groups of 2, series & parallel (making it a 24v/400ah bank right?) and still be good with the 40amp MPPT controller?
                I appreciate your time ✌️
                Don't blame yourself. A lot of people build small systems and then try to enlarge them without any direction.

                While no parallel wired battery system is good, going with a 24V 400Ah is better then the 12V system. Now remember that even though you have a 40Amp MPPT CC you still need the panel wattage to get to 40Amps.

                Based on a quick calculation 24V x 40A = 960 watts. So having 1000 watts that can provide at least 36Volts should be ok to charge a 24V 400Ah battery.

                So with 100watt panels you will need 10 of them wired in a series/parallel set up to the CC. You might be able to get away with 2 sets of 5 but the Voc total of those in series can't exceed your CC max DC input voltage. This is why going with 250watt panels make the wiring a little easier then using those 100watt lower voltage panels

                Now that battery system should safely provide you about 2400 watt hours each day (24V x 400Ah x 25% = 2400wh) but that may not be enough for what you want to power.

                There is more information in the Forum Stickie posts concerning off grid systems and how to design them.

                Comment


                • #9
                  Ok some things slowly coming into focus for me. As I realize more money will have to be spent, I’m also trying to determine how much of the system can be salvaged just by some reconfigurations? Before I go any further let me get some basics out of the way so I can make sure That I understand how the series/parallel world works.
                  1) Batteries - I should be able to take my 8 batteries (12v/100ah each) & put them into four groups of 2. Connect each group in series, now each group is at 24v/100ah. Next connect all 4 groups in parallel and this should give me a 24v/400ah bank.
                  Am I straight on that?
                  Next on the panels. I understand now what a mess the low voltage panel can make when trying for more power..and as much as I wish I could start over and get so some higher voltage panels I’m thinking bout the fact that I got 6 of these 100 watts already and would just need 4 more to follow your suggestion. So... I get a little more confused with the panels, though it seems the concept should be the same... but when I hooked the 6 up, grouped in series/parallel just like I wrote above with the batteries I calculated the current should have been 16.5amps tops. But like I said at one point I had a charge current of 30amps coming in? That messed my head all up there lol.. also how is wattage affected in a series/parallel connection? I always read about volts and amps but never wattage?

                  Comment


                  • #10
                    Originally posted by Iss_shaffer View Post
                    Ok some things slowly coming into focus for me. As I realize more money will have to be spent, I’m also trying to determine how much of the system can be salvaged just by some reconfigurations? Before I go any further let me get some basics out of the way so I can make sure That I understand how the series/parallel world works.
                    1) Batteries - I should be able to take my 8 batteries (12v/100ah each) & put them into four groups of 2. Connect each group in series, now each group is at 24v/100ah. Next connect all 4 groups in parallel and this should give me a 24v/400ah bank.
                    Am I straight on that?
                    Next on the panels. I understand now what a mess the low voltage panel can make when trying for more power..and as much as I wish I could start over and get so some higher voltage panels I’m thinking bout the fact that I got 6 of these 100 watts already and would just need 4 more to follow your suggestion. So... I get a little more confused with the panels, though it seems the concept should be the same... but when I hooked the 6 up, grouped in series/parallel just like I wrote above with the batteries I calculated the current should have been 16.5amps tops. But like I said at one point I had a charge current of 30amps coming in? That messed my head all up there lol.. also how is wattage affected in a series/parallel connection? I always read about volts and amps but never wattage?
                    Answer to your first question about the batteries. Yes you will have a 24V 400Ah system

                    With an MPPT type CC it really doesn't matter about the amps going in. It is the watts going into it. So 600watts charging a 24v battery should yield at max of 25Amp (600w / 24v = 25a).

                    If you had a PWM type CC then you want as many amps to go in as you can. But with a MPPT it is the wattage that you look for.

                    So what is the Vmp, Voc & Imp rating of those panels and how are they wired to the CC?

                    Comment


                    • #11
                      VMP - 18.0v
                      VOV - 22.4v
                      IMP - 5.55a
                      I see what you mean about the watts, what I meant to ask is do the watts add up regardless of connection? To say if you have six 100 watt panels hooked up together, will they be 600 watts no matter series, parallel or both?
                      So with a 2400 watt hour system would a 2500 watt inverter be more suitable? If so I reckon the 1/0 Cables on the bank will still be fine. I have 10awg coming from the panels that may need to be changed to 8awg for a 1000watt array? Just cause I went to 24v doesn’t change the fact that 10 is rated for 30amps right?

                      Comment


                      • #12
                        Originally posted by Iss_shaffer View Post
                        VMP - 18.0v
                        VOV - 22.4v
                        IMP - 5.55a
                        I see what you mean about the watts, what I meant to ask is do the watts add up regardless of connection? To say if you have six 100 watt panels hooked up together, will they be 600 watts no matter series, parallel or both?
                        So with a 2400 watt hour system would a 2500 watt inverter be more suitable? If so I reckon the 1/0 Cables on the bank will still be fine. I have 10awg coming from the panels that may need to be changed to 8awg for a 1000watt array? Just cause I went to 24v doesn’t change the fact that 10 is rated for 30amps right?
                        You are correct that the watts just add up when you use an MPPT CC.

                        Well that 2500 watt inverter is better but still big depending on what loads you are trying to start.

                        As for the wire between the panels and the CC. it will depend on the distance and if you can keep your voltage drop below 2%. That is one reason to wire the panel in series so you get a higher voltage that will be higher then you need for the battery voltage.

                        Comment


                        • #13
                          Ok, I started writing like I figured it out but then I started over thinking it and confused myself.. so.. it’s ok to have a higher array voltage as long as I don’t exceed my CC max input?which is 100vdc
                          thought #1-
                          Ten 12v/100 watt panels, in 2 strings of 5. Each string in series now at 60V. Now connect the strings in parallel putting the current at 11 amps.
                          thought #2-
                          Ten panels in 5 strings of 2. Each string in series, now at 24v. Connect the strings in parallel putting the current at 27.5.

                          So if with a MPPT CC It’s about the watts and not the amps.. so no matter which way you connect them the the amperage is determined by Watts / Volts right. Putting example #1 at 16.6 amps and #2 at 41.6 Amps.
                          so which way is correct if either? Sorry I’m being a pain, I just want to make sure I fully grasp this knowledge your giving me.
                          thanks ✌️

                          Comment


                          • #14
                            The problem with series wired panels is that you need to use the Voc voltage when determining the input to the CC. With a Voc of 22.4V you can only wire 4 of them in series to that CC. Which would allow up to 8 in a 4S2P configurations.

                            If you want to use all 10 of those panels you need to have them wired in 5 strings of 2. That will get you the input voltage high enough to charge a 24V battery (unless the Voltage drop is significant) and use all 10 panels. Using the Vmp rating of 18v that should get you about 36v input. Unfortunately you now need some type of combiner box with individual fusing for each of the 5 strings.

                            Again don't worry about the input amps. With an MPPT it is the input wattage that will determine the output amps.

                            Comment


                            • #15
                              Ok gotcha on that now.. and after looking at what I’m trying run I see I can drop down to a 2000 watt inverter. At first I was thinking, ok 2400 watt-hour system so I need a 2500 watt inverter to cover that, but now I see that is not the way to look at it. So pretty much the only cloudy area I have left now is the wire coming from the array.. it’s give or take Between a 100’-120’ run and during the tests I have conducted my input voltage coming in straight from the panels averaged between 32-33V, and that’s wired up for 24V. So with a vmp rating of 18V would you agree that’s a significant voltage drop? Looks like I made need to up that #10 to #8?
                              Last edited by Iss_shaffer; 06-04-2020, 10:42 AM.

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