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Running two charge controllers and their arrays through a common combiner box.

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  • Running two charge controllers and their arrays through a common combiner box.

    I just bought my second 40A MPPT solar charge controller 4215BN to expand my off grid solar system from 800w to 2000w. I read somewhere that f I am using a second controller, I should have an equal amount of watts and volts going through it as the other. Is that true? The charge controllers are identical twins.
    More compelling is my concern at running the second controller through my combiner box, where my system is set up now. Two 400w 48v arrays of 12v, 100w panels in parallel go through my combiner box. The negative wire screws onto the ground bar at the top, while the hot wire goes through a 20a breaker to the insulated (not grounded) hot bar near the bottom by the breakers. The charge controller panel inputs are attached by wires to the same ground and hot bar of the combiner box, so the panel current goes to the charge controller through the combiner box.
    The new addition: four 300w, 24v panels will provide 1200w in two 48v arrays in parallel (or I can wire the arrays into the combiner box separately, which also parallels them.), Open circuit = 40v per panel, short circuit just under 10 amps. Each two panels in series = about 80v open circuit. My existing arrays also have an open circuit of 80v. If I run the new system through the combiner box, the energy from all panels will be combined on the hot and ground bars and be connected to both charge controllers at the same time. That should parallel two 80v open circuit systems. The max voltage for my controllers is 138v. Will this put too much voltage on the controllers, or will the voltage remain at 80 while amps increase?
    Also, my current arrays produce up to 11 amps. The additional panels add 10 amps per panel or 10 amps per two in series equalling 20 amps when joined in parallel with the other two 24v panels attached in series to form a 48v array. If my calculations are correct, that should add up to 31 amps on my 40 amp chargers.
    I have room for another array of four 100w, 12v panels on the structure I built for my new panels. If I add another 400w, 48v array to my system, that will add an additional 5.4 amps each 100v panel is rated at, while retaining the 48v, 80v open circuit to the charge controllers. Total: 80v open circuit on a charge controller rated for 138v open circuit and 36.4 amps when charge controller is rated 40 amp.
    Could I do this with just one charge controller, or is there an advantage in using two through a common combiner box?

  • #2
    Each array * should have it's own controller & own combiner box. no mixing or sharing between them except the grounding rod and the batteries at the end
    .
    I have 2 brands of controllers, and 2 differently sized arrays. The controllers don't care, the batteries don't care (2kw & 3kw)

    Each controller needs it's OWN combiner box, because each controller will try to adjust the MPPT point on the PV to the best point. 2 controllers on a common array will never find the right MPPT point.


    * If you are using a virtual tracking array, 10 panels facing east & 10 panels facing west, AND the panels are identical, you can share a controller & combiner box.

    But someone is feeding you a line "i read somewhere" because it ain't so.

    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

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    • #3
      Mike90250, Sounds like good advice. I will have to get some 2awd cables and another combiner box to connect a second system to the battery bank and to the inverter. My 5000 PS inverter has three sets of connect posts. The current going through the combiner box to the inverter brings in DC from the common battery bank, so it should be delivering the same 24v and amperage to the inverter.

      In the meantime, however, since I just received my panels (3 of 4, as one "disappeared" during shipping) and because the addition of the new array should still be within the max volts and amps of the charge controller, I might just add the new 1200w, 48v array to the 800w, 48v array to the controller through the combiner box. The two 48v arrays, one with 11amps max and the other just under 20amps will parallel on the hot bar of the combiner box, carrying a 48v current up to 31 amps to the 40 amp charge controller. Because the charge controller is getting the current from a singular source (wire from the combiner box hot bus bar), what difference does it make if one 48v source is paralleled with another with lower amps? The voltage remains the same and the amps change as the sun changes position anyway.

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      • #4
        Originally posted by Tedx View Post
        .....
        .....I might just add the new 1200w, 48v array to the 800w, 48v array to the controller through the combiner box. The two 48v arrays, one with 11amps max and the other just under 20amps will parallel on the hot bar of the combiner box, carrying a 48v current up to 31 amps to the 40 amp charge controller. Because the charge controller is getting the current from a singular source (wire from the combiner box hot bus bar), what difference does it make if one 48v source is paralleled with another with lower amps? The voltage remains the same and the amps change as the sun changes position anyway.
        for a MPPT to charge a 48V bank, your PV array should be about 90V ? Are both your PV arrays Vmp closely matched to provide about 90V to the controller ? The array voltage will be clamped to the voltage of the lowest voltage array, so if one is 103V and the other is 94V the max voltage it can provide power at is 94V to the controller. The wider the voltage difference, the more power lost.

        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


        • #5
          The max open circuit voltage of my 800 watt 48v array is 90v. (two sets of 12v panels in series, then paralleled, each panel at 22v max. The open circuit voltage of my new array will be 80v (two pairs of 300w, 24v panels in series, then in parallel, each panel with 40v max open circuit. My battery bank is 24v. I use a MTTP controller.

          However, I was just reviewing the specs on my controller and it states that 1040 watts is the max input from panels, so I have to set up a second controller anyway. But my new array is 1200w, and I already bought the additional controller that limits itself to 1040. If the voltage and amps in the 1200w system are well within the controller's limits, Do you think I could use it with 1200w? It's only a mere 160w difference.

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          • #6
            You can over panel many MPPT controllers. They will max out at their rated output. Many people over panel, especially in less than optimum solar conditions.
            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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            • #7
              littleharbor, That's good. Today I found a Renogy 40a 12/24v converter with almost identical specs as the one I bought at the Home Depot site. It costs the same. It identified max open circuit voltage and amps, but said nothing about max panel input. I have inquired on the site if such a requirement stands.

              Here is what I don't understand: Open circuit max voltage for my controller is 138v. My current array delivers about 90v open circuit (2 arrays of four 12v 100w panels in series, each with 22v open circuit.) The amperage is 5.4 per panel, so when I parallel it with the other set of four in series, my amp power is about 11a.
              My new array I am putting together features four 300w, 24w panels. Two pairs in series makes it a 48v series with about 80v open circuit (38.2v each) Each panel provides 9.2a, so when paralleled with the other pair in series, it makes just under 20a at open circuit voltage of about 80v. If I run the new array through my combiner box into the 40a charge controller, I would get a combo of an 80v max array and 90v max array paralleled on the breaker bars, making about an 80v current with 11a + 20a = 31a. The voltage would be well within the 138 max open circuit voltage and the 31 amps are well within the 40 amp limits of the controller. But the panel input is well over the 1050 set by the manufacturer. Is this because the MTTP controller would change volts to amps while charging a 24v battery bank from 48v arrays?

              Comment


              • #8
                As shown in the below chart the rated charge power, which will not increase is what it is. As you can seethe maximum PV array can be substantially higher without damage to the controller.

                As to your question, you're right, The controller will increase the charging current up to the max output of the controller.


                EP max panel power chart.jpg
                Last edited by littleharbor; 09-06-2018, 07:46 AM.
                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                • #9
                  littleharbor, Got it. On review of my manual, I observed that I had read the "Rated Power Charge" as "Max PV Array Power". Does that mean charging power is limited to "Rated Power Charge" regardless of additional PV Array Power? I am trying to determine if I should deploy my second charge controller and accessories to accommodate increased PV Array. The maximum Array Power will be 2400w on the 24v system.

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                  • #10
                    I just got lucky as a result of a botched Amazon Prime delivery. Only three of four panels I ordered arrived (sounds like someone in the shipping business has a new 300w panel.) First Amazon was going to resend the order and have me pull out one of the panels. Then I got an email saying I could take the replacement order in full and keep the three panels I originally received. That's about $1000 in free panels. Not bad for an amenity.

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