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Quick question- parallel then series

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  • Quick question- parallel then series

    I have 8 100 watt panels. They are 12 volts and 5 amps. My MPPT controller only goes up to 30 amp. Can I wire four of them in parallel and then wire the other four in parallel then connected the two sets in a series for 24v but under 30 amps?

    Thanks in advance
    Last edited by muskogeezeke; 06-23-2017, 07:19 PM.

  • #2
    What is your system voltage? What specific mppt controller are you using?

    If a 12 V battery, you are looking at 67 charging amps at STC conditions and 100% mppt efficiency. If a 24 V battery, the maximum output under those conditions would be 33 A.

    Most decent charge controllers will limit their output to their rating, so even if the array was capable of producing more, it would limit itself to 30 A.

    You might be able to wire 4 in series to bring the series voltage to 88 Voc... that is safe on a 150 Voc rated controler, but could be trouble on a 100 Voc rated controller if you live someplace with cold weather.

    Putting two strings in parallel would deliver a combined 10 A at something around 70 V, which should be fine for your mppt controller to accept.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      Originally posted by sensij View Post
      What is your system voltage? What specific mppt controller are you using?

      If a 12 V battery, you are looking at 67 charging amps at STC conditions and 100% mppt efficiency. If a 24 V battery, the maximum output under those conditions would be 33 A.

      Most decent charge controllers will limit their output to their rating, so even if the array was capable of producing more, it would limit itself to 30 A.

      You might be able to wire 4 in series to bring the series voltage to 88 Voc... that is safe on a 150 Voc rated controler, but could be trouble on a 100 Voc rated controller if you live someplace with cold weather.

      Putting two strings in parallel would deliver a combined 10 A at something around 70 V, which should be fine for your mppt controller to accept.
      100 Voc. I'm in central Oklahoma, so it can get cold but it really is a crapshoot.

      But in theory would what I suggested work?

      Comment


      • #4
        Originally posted by muskogeezeke View Post

        100 Voc. I'm in central Oklahoma, so it can get cold but it really is a crapshoot
        That would be cutting it close. Probably safer to just put two panels in series, and then put the four two-panel strings in parallel. You should fuse each of the strings before combining it with the others... In-line fuses with MC4 connectors and basic MC4 Y-type combiners should be OK, your combined current will still only be 20 A.

        What you originally suggested (4 in parallel, put in series with another 4 in parallel), seems sub-optimal for any electrical mismatch that might exist between the panels, and for shade response. You would also need to fuse each individual panel, instead of just each series pair.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

        Comment


        • #5
          Originally posted by sensij View Post

          That would be cutting it close. Probably safer to just put two panels in series, and then put the four two-panel strings in parallel. You should fuse each of the strings before combining it with the others... In-line fuses with MC4 connectors and basic MC4 Y-type combiners should be OK, your combined current will still only be 20 A.

          What you originally suggested (4 in parallel, put in series with another 4 in parallel), seems sub-optimal for any electrical mismatch that might exist between the panels, and for shade response. You would also need to fuse each individual panel, instead of just each series pair.
          That's how I have it wired now but not getting more than around 6 amps. Not sure what I did wrong.

          Comment


          • #6
            Originally posted by muskogeezeke View Post

            That's how I have it wired now but not getting more than around 6 amps. Not sure what I did wrong.
            Which way do you have it wired now?

            The amount of current you get may be influenced by the battery's state of charge. A full (or mostly full) battery in float or absorb will not accept full current.

            Beyond that, the current will also be typically less than the rated amount because the actual angle of the sun and ambient temperature affect output.

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

            Comment

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