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  • 12v/24/48v parallel or series? Confused!!

    OK I've looked this up several times and it really is confusing lol. I understand parallel, I understand series. What I don't really understand is how u keep series from going above 24v? I think what I've been looking up is its best to do 24v battery back up and a total system rather than a 12v battery back up and system for a house... is that correct.

    I am about to have a 1.5kw system arriving at the house in a few weeks, 13 100 watt panels and a 200 watt panel. (I won it all on bid on ebay for like $700 with 2 invertors and 2 battery controllers, cables, mc4 connectors and all to do the system. I know it goes from the panels to the controller to the batteries and then the inverter... or I think

    but again I get confused with what's best? I think 24v is but when you hook two 12v panels together u get 24v in series, so If I connected another in series would that bring it to 36v? If I did a 24v battery bank which I thought was preferable wouldn't 36v be bad? I know the wattage isn't going to change but I'm so confused on how to maintain a solid 24v? Do you just keep hooking two panels in series to 24v and do that every 2 panels or what? Lol I am probably making this a lot harder than I think but maybe you all can help!! Thanks guys

  • #2
    The common battery bank voltages for which equipment is produced and sold in large quantity are 12, 24, (36) and 48.
    Most do not go above 48 since it puts their installation into a different safety category under the National Electrical Code (NEC).
    36 is common for golf carts but not for PV systems.
    The higher the voltage the lower the current for the same power and the less money you have to spend for larger copper or aluminum wires.

    On the panel side, you can take two nominal 12V panels and put them in series to charge a 24V battery through a PMW (inexpensive, different design) CC.
    If you use a more expensive and efficient MPPT type CC you can work with a panel string voltage that is much higher than the battery voltage and still make use of all of the available panel power.

    You can get a lot of this information and more by reading the sticky threads in the Off Grid topic area of the Forum.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Yeah I've tried to do a lot of research on this and I kept getting directed to this forum so I was like we'll Ill just make an account here and ask the folks the specific question I have since I couldn't really find a direct answer... so basically if u get a mppt controller it doesn't matter if u hook up say 13 12v panels in series which in turn would create 156 volts. It would bring it down to 24v to charge say a 24v battery bank or something? I'm trying to do a grid tie system but have a battery back up to power the house when the power goes out or slowly work my way off grid.

      would the mppt controller use the rest of the watts and amps? Or the other say 122 volts that the series panels produce? Lol hopefully you all don't get mad at my stupidity!

      Comment


      • #4
        And now I've looked up these MPPT controllers and finding a lot of them only accept up to 150 and 200 volts? Well even if u did 13x250watt panels you could only have a 3250 watt system. 13x12v would be 156 volts which is right at the max. So how do you find.ones that can handle say 400 to 600 volt input? I'd probably need a decent sized system to be off grid so I'd need a pretty big MPPT controller, or do you.need 2 separate ones or? Lol thats if I'm even understanding this series thing correctly and if it's even the best route to go?

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        • #5
          Originally posted by Brandon8791 View Post
          And now I've looked up these MPPT controllers and finding a lot of them only accept up to 150 and 200 volts? Well even if u did 13x250watt panels you could only have a 3250 watt system. 13x12v would be 156 volts which is right at the max. So how do you find.ones that can handle say 400 to 600 volt input? I'd probably need a decent sized system to be off grid so I'd need a pretty big MPPT controller, or do you.need 2 separate ones or? Lol thats if I'm even understanding this series thing correctly and if it's even the best route to go?
          You don't try to find high input voltage, you put more strings of the same length in parallel to work with the size controller you have.

          Once you get beyond 100V or so on the panel side there is less benefit to be gained from making the wires smaller.
          If the two strings are going to have different shading or temperature conditions, then each string would need to go into its own MPPT input.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

          Comment


          • #6
            So I'm confused do my panels need to be parallel or series to charge a 24v battery bank, lol see I'm getting confused on what's happening. Or do I need to just stick with a 12v panels and do 12v battery bank? My panels.I believe are all going to be 12v or 18v max I think, but if I did them.in parallel the voltage would stay 12v which wouldn't charge a 24v system I thought, so it'd have to be series. And if I did series then I thought the mppt controller is a lot more efficient and it's a lot more efficient with the solar panels as well cuz it basically multiplies to voltage which means less watts and amps is wasted. Like say the sun just came up each panel is producing 4 volts, in parallel that's not enough to charge a 12v battery bank, but in series with say 4 panels, that's 16 volts Which will charge the system. So nothing is thrown away.


            so are u saying I'd have to create a separate system every 3kw? To stay under the 150 volts inputed to the MPPT? or how do I do parallel but keep the voltage up lol like I said I am so confused it's unreal but I want the most efficient system I told myself that if I'm going to do this then I'm going to do it right

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            • #7
              Hmmm.... well now I've looked up the enphase inverters but I don't think that would work with a battery back up lol guess u can't have best of.both world's on that either >.>

              Comment


              • #8
                OK, I've surfed to find you a couple pictorial examples. I in no way able to explain Series and Parallel circuits. There are many basic electricity sites that already do that,

                The limits you need to set are

                1) ARRAY VOLTAGE.
                If you are using a 24V inverter, then you don't want to wire your panels to more than 100V The higher voltages push the MPPT controller into less efficient operating ranges as it downconverts your array voltage to battery voltage. (if a 12V inverter system 75V is the highest you should design for)

                2) PARALLEL PV Strings need fuses
                More than 2 parallel strings need a fuse on each string

                Ideal, if you could stay at 2 parallel strings (5 series panels ea) without overvolt on the controller. there will be a sticker on the back of the panel and we will need these values to completely spec this out,

                sample:
                Vmp = 18V
                Voc = 22v
                Isc = 5
                Imp =4.5
                Series fuse = 7A
                The Voc is the value used to determine controller overvoltage So a Classic 150 could have up to 6 of these <sample> panels in series. 7 will kill it @ 154V

                sample pics parallel-series-circuit-x16.jpg
                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


                • #9
                  Ah ok, so you basically don't wire all the panels together you have to separate them into different sets? (Or ig strings) like 1 set of 6 panels, another set of 6 panels? I'm basically getting 13 windynation 100 watt polycrystalline panels, and one 200 watt macht monocrystalline panel to total a 1.5kwhile system. The reason it's different is because I won all this on auction with 2 1500 watt modified sine wave inverters, 2 p30l battery controllers and 2 50 foot mc4 connector extensions with bare wire on the ends to connect to the controller... I won all this stuff for like $785 so I thought it was a fair price and would get me somewhere.

                  Attached Files

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                  • #10
                    This is basically an overview of everything.I'm getting x2

                    then 1 separate panel with another controller, and then the 200 watt mono panel pictured above in last reply

                    also I might add that I don't mind one bit to upgrade the inverter or controller, lol I just bought the kits and such cuz I knew it was a great price, especially for the panels. So any insight on that is great.

                    and I'd also like to add that I definitely appreciate the information and I've been researching this literally for.hours a day and watching videos trying to.make sure I understand.this fully before everything gets here (2-5 weeks) it's all coming from China air mail so it'll take some time.

                    hopefully I have provided adequate information to help you guys.understand.and not only that but help me understand the series/parallel and what.needs to go where I guess, I'm guessing I have to separate so many panels to different controllers...

                    I think I'm understanding it as like 6-8 panels in series goes into one controller and that goes into one set of batteries set up in series for 24v? Then another 6-8 panels into another controlled and another battery bank? And just keep it all separate am I understanding that correctly? If not feel free to correct me!
                    Attached Files
                    Last edited by Brandon8791; 01-05-2017, 01:30 AM.

                    Comment


                    • #11
                      Well, you sure have a mixed bag of stuff there. Some you can sell to get cash to get parts you will need, I suppose.
                      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


                      • #12
                        Originally posted by Brandon8791 View Post
                        Yeah I've tried to do a lot of research on this and I kept getting directed to this forum so I was like we'll Ill just make an account here and ask the folks the specific question I have since I couldn't really find a direct answer... so basically if u get a mppt controller it doesn't matter if u hook up say 13 12v panels in series which in turn would create 156 volts. It would bring it down to 24v to charge say a 24v battery bank or something? I'm trying to do a grid tie system but have a battery back up to power the house when the power goes out or slowly work my way off grid.

                        would the mppt controller use the rest of the watts and amps? Or the other say 122 volts that the series panels produce? Lol hopefully you all don't get mad at my stupidity!
                        Unfortunately that hardware is for off grid only. You will never get approval from your POCO or the AHJ to connect to the grid without a UL listed grid tie inverter.

                        Also if you want to have a battery backup system you will need to get a hybrid inverter that can charge a battery system as well as connect to the grid. Those are not cheap.

                        Comment


                        • #13
                          I have some bad news for you, as if you need more. I wouldn't hold my breath waiting for this to arrive. Most likely, IT WON'T. I have seen these incredibly good deals come up on ebay before. I have actually purchased similar "deals" myself, rather skeptically, I might add. Of course when all is said and done you should get your money back after a painful process with ebay.
                          Think about it. You're not going to get 4 100 watt panels, inverter, charge controller and all the other accessories for $145.00, ANYWHERE. Also you're not going to get said panels and all other goodies shipped from China for $35.00.
                          I'm sorry to have tell you this but better you know now than a month from now while you are anxiously awaiting your delivery. I saw these listings last week myself and watched all the bids come in knowing full well there will be a bunch of really bummed ebay customers.
                          Last edited by littleharbor; 01-05-2017, 10:46 AM.
                          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                          Comment


                          • #14
                            Hopefully, it'll all come through. The eBay user has really good ratings from several people, so I somewhat believe this one. I could understand if they had just two people saying they did great, but when it's from 70-80 people I don't think it's a scam. They only thing I don't like is they didn't provide tracking. We can hope for the best!

                            Back on topic though, did I explain everything correctly when I described how to hook everything up?

                            Comment


                            • #15
                              You cannot use 13 panels on any controller. No PRIME numbers allowed as that only leaves you with 2 possible configurations of all in series or all in parallel. A 250 wat pannel has a Voc of roughly 30 volts. Do the math, 13 x 30 volts = 390 VOLTS. Not going to happen.
                              MSEE, PE

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