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Will this set up work , need a little help here.

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  • #16
    Originally posted by sensij View Post

    Huh? These are 72 cell panels, they produce enough voltage wired in parallel to support a 24 V battery for either PWM or MPPT. That downside to wiring three in parallel is that after they are combined, the circuit would have 26.1 A Isc, requiring wire rated to carry 1.56x that, or 40.7 A. That means 6 awg from the panel combiner to the charge controller, and each individual panel must be fused at 20 A max.
    Singly, Or paralleled The voltage is 24 volt nominal. Keeping the voltage at this level is defeating the whole point of using an MPPT controller. Plus you are having to push higher amperage to the controller. What's the point of using a high dollar MPPT controller if you are going to keep the voltage at a level that an inexpensive PWM controller can handle?
    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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    • #17
      Originally posted by littleharbor View Post

      Singly, Or paralleled The voltage is 24 volt nominal. Keeping the voltage at this level is defeating the whole point of using an MPPT controller. Plus you are having to push higher amperage to the controller. What's the point of using a high dollar MPPT controller if you are going to keep the voltage at a level that an inexpensive PWM controller can handle?
      It doesn't defeat the whole purpose. The mppt will still be more efficient... it will operate at the maximum power point (Vmp = 36.6 V at STC), instead of the battery voltage (24-28 V). That extra bump in voltage results in more power in most conditions, except when it is very hot and the Vmp falls to close to the battery voltage anyway. Mppt also offers better protection against too much current during charging, not really an issue in this case, but the ability to move the panels away from maximum operating point to limit current is not something a PWM controller can do, necessarily, if it is only looking at voltage (some controllers may be better than others at recognizing high current and reducing the PWM duty cycle).

      I'm not saying that I'm recommending three panels, but there is a difference between saying it won't work, which is how your response looked, than saying it just isn't the ideal way to use the equipment. If you look at mppt efficiency curves, they generally get more efficient as panel voltage gets close to battery voltage... not enough to overcome the other disadvantages of running 3 panels in parallel, but at least a little bit to help.

      OP wrote that the 50 A mppt controller is already owned. If he'd rather use it with three panels in parallel and pay the extra money for wire and over-current protection, while still generating less than 2S2P... his money, his choice. Maybe there isn't room to mount the 4th panel, who knows.


      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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      • #18
        My panels say on the back 8. 6 amps or something . So I figured that's a total of a little over 24 amps and the mppt controller is rated at 50 amps.
        your saying I want to connect in series and get more volts keeping the amps the same? Am I getting that right?
        for that I need 6 awg cables from panels to controller?

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        • #19
          When you connect in series the amperage will stay the same as a single panel, yes. The MPPT controller will do the voltage conversion and give you the sum of the amperages,or thereabouts.
          Do you have space to mount all 4 panels?
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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          • #20
            Originally posted by sensij View Post

            It doesn't defeat the whole purpose. The mppt will still be more efficient... it will operate at the maximum power point (Vmp = 36.6 V at STC), instead of the battery voltage (24-28 V). That extra bump in voltage results in more power in most conditions, except when it is very hot and the Vmp falls to close to the battery voltage anyway. Mppt also offers better protection against too much current during charging, not really an issue in this case, but the ability to move the panels away from maximum operating point to limit current is not something a PWM controller can do, necessarily, if it is only looking at voltage (some controllers may be better than others at recognizing high current and reducing the PWM duty cycle).

            I'm not saying that I'm recommending three panels, but there is a difference between saying it won't work, which is how your response looked, than saying it just isn't the ideal way to use the equipment. If you look at mppt efficiency curves, they generally get more efficient as panel voltage gets close to battery voltage... not enough to overcome the other disadvantages of running 3 panels in parallel, but at least a little bit to help.

            OP wrote that the 50 A mppt controller is already owned. If he'd rather use it with three panels in parallel and pay the extra money for wire and over-current protection, while still generating less than 2S2P... his money, his choice. Maybe there isn't room to mount the 4th panel, who knows.

            ok well, how exactly would you set it up with the equipt I have. What the most efficient way?
            i can use all 4 , I will just have to return my 3 branch connector for a 4 branch. ( is there another way to connect all the panels without buying a branch type connector)?
            I wanted to use the 4th panel for lights in a tiny home, but I can buy another.

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            • #21
              Originally posted by littleharbor View Post
              When you connect in series the amperage will stay the same as a single panel, yes. The MPPT controller will do the voltage conversion and give you the sum of the amperages,or thereabouts.
              Do you have space to mount all 4 panels?
              Yes

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              • #22
                Then your best approach would be to series wire two panels at a time and parallel those two strings. 2S2P. You will have 70 - 72 volts @ 17.2 amps and get 34+ amps into your batteries No fusing needed for the panel input, Good voltage input and you can use all 4 panels.
                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                • #23
                  Originally posted by Russelljw View Post

                  ok well, how exactly would you set it up with the equipt I have. What the most efficient way?
                  i can use all 4 , I will just have to return my 3 branch connector for a 4 branch. ( is there another way to connect all the panels without buying a branch type connector)?
                  I wanted to use the 4th panel for lights in a tiny home, but I can buy another.
                  In this post, I walked through what it would look like if you used 4 panels, with two in series, and the two series strings combined with a Y connector instead of a 3 branch connector. The two panels in series are wired directly to each other, + to -, with the + of one and the - of the other getting combined with the +and - of the other string wired the same way. Fortunately, MC4 connectors make it hard to mess up.


                  https://www.solarpaneltalk.com/forum...015#post351015

                  I'm uncomfortable giving much more advice in this thread, because your familiarity with safe electrical design seems low enough that i can't trust you will execute the advice safely. You still haven't posted the capacity of the battery, which is important to consider in all this.
                  CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                  • #24
                    Originally posted by Russelljw View Post
                    My panels say on the back 8. 6 amps or something . So I figured that's a total of a little over 24 amps and the mppt controller is rated at 50 amps.
                    your saying I want to connect in series and get more volts keeping the amps the same? Am I getting that right?
                    for that I need 6 awg cables from panels to controller?
                    There is part of your oversight and not understand the benefits of MPPT.

                    First Input current has nothing to do with output current. On MPPT Output Current = Panel Wattage / Battery Voltage. So you have 1200 watts / 24 volts = 50 amps

                    Now what you are missing out on is efficiency and a lot of cost savings. When you put al 3 panels in parallel will mean you have to use large wire which is expensive. If also means with 3 panels you are now required to use a combiner and Fuses Breakers which are expensive. Wire them all in series, you use inexpensive 14 AWG wire an no expensive fuses and expensive combiners and all the hardware required. You are shooting yourself in the foot spending money you do not need to or have use for. You are just putting more eggs in the basket to break, and paying more for the inconvenience and lost power you will never get back.
                    MSEE, PE

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                    • #25
                      Originally posted by sensij View Post
                      I'm uncomfortable giving much more advice in this thread, because your familiarity with safe electrical design seems low enough that i can't trust you will execute the advice safely. You still haven't posted the capacity of the battery, which is important to consider in all this.
                      You finally woke up to that after all these years? Why do you think I am so hard on DIY's?
                      MSEE, PE

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                      • #26
                        What gauge wire is needed for each part?
                        Where fuses ? What size fuses?

                        what does 2s2p mean? Where can I find a diagram of series wiring 2 panels and paralleling those two strings?
                        thank you

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                        • #27
                          Originally posted by Russelljw View Post
                          What gauge wire is needed for each part?
                          Where fuses ? What size fuses?

                          what does 2s2p mean? Where can I find a diagram of series wiring 2 panels and paralleling those two strings?
                          thank you
                          2S2P = 2 in series, 2 in parallel.
                          MSEE, PE

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                          • #28
                            Just trying to learn

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                            • #29
                              This is a set up is out of necessity , my family will be living off grid all summer until nov.
                              it's got to work.
                              so thank you for your help

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                              • #30
                                Hopefully you understand the difference between series and parallel. First you connect 2 panels in series, then connect the other 2 in series. Now you connect the 2 pairs in parallel, That's what 2S2P is.






                                Series_Parallel_Connecting_Solar_Panels.png
                                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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