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  • Newbie question about making 3-to-1 parrallel mc4 connectors

    Is there an electrical reason why a person cannot make their own 3-to-1 parrallel mc4 connections? For example:
    3x 100w panels
    max amperage per panel is about 5.6amps/each
    total amperage in parrallel would be about 16.8amps
    sooooo.......
    all wiring is using 10awg (30amp max) wire....

    Projected Result is:
    the 3x POS+ connections are parralleled at the 3 panels down to 1x 10awg (30 amp) wire using a 6awg insulated butt-connector.
    the 3x NEG- connections are parralleled at the 3 panels down to 1x 10awg (30 amp) wire using a 6awg insulated butt-connector.
    --------------------------------
    Reality output is:
    the 3x parralled 100w panels are producing 12.9v and 1.1amp (cloudy day and battery bank is a little low).........but..........
    connecting a 4th stand-alone 100w panel on its own 10awg wiring....bumps voltage to 13.1 and JUMPS amperage to 3.6 amps (which is a 2.5amp increase).

    EDIT: (I do generally understand that "voltage" is affected by the charge level of the battery bank, and also that the charge amperage is "manipulated" by the PWM CC.............but there is an undeniable fact that 1 panel alone, under all the same conditions, is adding more amperage than the 3x parralleled panels combined)..

    This 2.5 amp increase from ONE PANEL ALONE is producing more amps than the THREE (3x) PANELS (parralleled) COMBINED!!!!
    (2.5 amps x 13.1v on a PWM cc = 32.75w;........for a 100w panel on a cloudy day sounds quite reasonable)
    ------------------------------------------
    So is there something this newbie did not predict about the behavior of diodes (or ANYTHING) in parralleling the connections???.......or is it likely that 1 or more panels are not functioning due to the shipping "mishandling"?? I wish I had time to check each panel independantly right now.....but that requires me to disconnect the battery bank many times, climb up the roof many times, plug in each panel independantly many times, climb back down many times, and reconnect the battery bank many times..... However, I have to sleep now, go to work as soon as I wake up (when my wife gets home), go do boy scout stuff with my son in the morning, sleep again, go to work again..........and MAYBE get an opportunity to test the panels independantly on Sunday morning. So, please, any input about why "electically" these 3 panels are producing such low output using a fabricated "parrallel connection",......please let me know so I can be pondering it between now and Sunday/Monday.?

    Thanks in advance, and I apologize for the book I have written. I just want to be thorough...

  • #2
    The plan is to use 1 pair of 10awg wires PER "3x 100w panels." The 3 on the left are paralleled down to 1 pair of wires (at the panels). The 4th panel on the right, is plugged solo directly into it's own pair of 10awg wires (for now...until I get the next 2 panels). 20161104_112303b.jpg
    Last edited by tb144050; 11-04-2016, 01:58 PM.

    Comment


    • bcroe
      bcroe commented
      Editing a comment
      It appears you are using 18V (36 cell) panels to charge a 12V battery. Remember that
      any junctions on the roof need to be water tight; how is your butt connector? You can buy
      2 into 1 MC4 units; 2 100W panels into each 10 gauge might work OK.

      At low voltage you need to be more concerned about efficiency; power lost in the wire
      resistance. Any significant voltage drop in the wire will come out of your production,
      even if the wire is well under capacity. What might work better, is put 2 panels in
      series feeding a 10 gauge, but the voltage generated will require an MPPT charge
      controller. 250W or 300W panels could replace 2 or 3 of your 100W in this setup,
      with a lot more output per $.

      I check panel performance with a clamp on DC meter. To remove variables of sun
      and battery, you could go up there in good sun and short the panel outputs. Put
      the meter on a lead from each panel; they ought to all read about the same.
      good luck, Bruce Roe

  • #3
    My guess is that you have a wiring issue with the first 3 panels.

    If all 4 of those panels have the same Vmp & Imp then wiring them in parallel should result in a voltage measurement ~ Vmp. And the current measurement ~ 4 x Imp at Noon on a sunny day with a battery bank that needs charging. In reality the current measurement will probably be ~ 4 x (80%) Imp because the Imp is per factory test under perfect conditions.

    If you are getting voltage reading much lower then the Vmp I would say you either have a wiring connection problem or high resistance due to long cable lengths which is causing a high Voltage Drop.

    Comment


    • #4
      Originally posted by tb144050 View Post
      Is there an electrical reason why a person cannot make their own 3-to-1 parrallel mc4 connections?
      No. In fact those are available off the shelf.
      the 3x parralled 100w panels are producing 12.9v and 1.1amp (cloudy day and battery bank is a little low).........but..........
      connecting a 4th stand-alone 100w panel on its own 10awg wiring....bumps voltage to 13.1 and JUMPS amperage to 3.6 amps (which is a 2.5amp increase).
      What gauge wire do you have between your three existing panels and your battery, and how long is it? You may have an unexpectedly high resistance there; that would explain what you are seeing.
      I wish I had time to check each panel independantly right now.....but that requires me to disconnect the battery bank many times, climb up the roof many times, plug in each panel independantly many times, climb back down many times, and reconnect the battery bank many times.....
      Much simpler test - wait until you see that happen again, then measure voltage at the input to the CC and voltage at the array. If they are very close, then it's not the wiring - it's the panels. If there is a many-volts drop, you have a wiring issue.

      Comment


      • #5
        Originally posted by SunEagle View Post
        My guess is that you have a wiring issue with the first 3 panels.

        If all 4 of those panels have the same Vmp & Imp then wiring them in parallel should result in a voltage measurement ~ Vmp. And the current measurement ~ 4 x Imp at Noon on a sunny day with a battery bank that needs charging. In reality the current measurement will probably be ~ 4 x (80%) Imp because the Imp is per factory test under perfect conditions.

        If you are getting voltage reading much lower then the Vmp I would say you either have a wiring connection problem or high resistance due to long cable lengths which is causing a high Voltage Drop.

        Without time to inspect it until Sunday, I cannot imagine what I could have done incorrectly on a simple parrallel connection (x2). The length of cable to the 3-paralleled panels is about 35-40 foot of 10awg. I assumed this was thoroughly large enough to compensate for the length (if even needed). The length of cable to the 1 solo panel is about 5foot shorter (30-35foot length). All 4 panels are same model, ratings, etc. Just "mishandled" (see other post) before I received them.

        Comment


        • #6
          Originally posted by jflorey2 View Post
          No. In fact those are available off the shelf.

          What gauge wire do you have between your three existing panels and your battery, and how long is it? You may have an unexpectedly high resistance there; that would explain what you are seeing.

          Thanks for confirming that there is no difference between "fabricated" and "off the shelf." As a newbie, I first suspected that it may require diodes or some gizmo because "path of least resistance leads to another panel" or blah blah blah (some other unknown information about solar powered systems). All wiring is 10awg, including between the PWM cc and the battery bank. Lengths of panel wires are described in my previous reply (above).....length of the 10awg wiring from PWM cc to battery bank is about 8ft.

          (Note: When I step up to 6 panels, Imp will require me to upgrade the "cc core setup" and the wiring to the battery bank........but for now, 4x 100w panels on a cloudy day "should" be withing acceptable limitations of a 20amp PWM cc and 30amp 10awg wiring..........atleast on the meters, I am at 1.1amp with the 3 panels, and up to 3.6amps with the 4th panel....still way below the cc limitation of 20amp. But the word "should" always bothers me when I can't figure something out.)
          Last edited by tb144050; 11-04-2016, 01:56 PM.

          Comment


          • #7
            To run 35 to 45 feet over 10 awg. you need a much higher array voltage and an MPPT charge controller. I assume you are using a PWM CC, Yes something is also incorrect with the 3X100 watt panels in parallel.

            Comment


            • #8
              Are those panels mounted to 2X2's? are the 2x2's secured to the roof?

              Comment


              • #9
                Originally posted by tb144050 View Post


                Without time to inspect it until Sunday, I cannot imagine what I could have done incorrectly on a simple parrallel connection (x2). The length of cable to the 3-paralleled panels is about 35-40 foot of 10awg. I assumed this was thoroughly large enough to compensate for the length (if even needed). The length of cable to the 1 solo panel is about 5foot shorter (30-35foot length). All 4 panels are same model, ratings, etc. Just "mishandled" (see other post) before I received them.
                I am assuming the 100watt panels have the following ratings. Vmp ~ 18VDC and Imp ~ 5.5A.

                Then using the 18VDC and 3 x the Imp or a total amperage of ~ 16amps, a #10 wire needs to be shorter than 10 feet to keep the VD below 2%. At 40 feet you will need to use a wire around #4 or larger.

                Comment


                • #10
                  bcroe, I just saw your comment way above on the picture. Thanks for the suggestion. I am sleepy and did not remember that my voltmeter also works up on the roof to check Open-Circuit voltage of each one indepentently....without multiple tasks up and down the ladder. I might be able to take 15 minutes to do that tomorrow if I am lucky. Thanks for reminding me of the obvious.
                  -----
                  I am off to get 4 hours of sleep before a 12 hour night shift. I look forward to reading more of the helpful replies when I take my lunchbreak at midnight.

                  Comment


                  • #11
                    Originally posted by SunEagle View Post

                    I am assuming the 100watt panels have the following ratings. Vmp ~ 18VDC and Imp ~ 5.5A.

                    Then using the 18VDC and 3 x the Imp or a total amperage of ~ 16amps, a #10 wire needs to be shorter than 10 feet to keep the VD below 2%. At 40 feet you will need to use a wire around #4 or larger.

                    Very helpful insight. Is there a formula to calculate the voltage drop at 40ft, given the parameters of this setup? Even still, my newbie mind still does not understand why an expected paralled current of ~ 10-15amps (cloudy day, 3 panels) drops to 1.1 amp.......but I successfully receive 2.5amp from 1 panel on 10awg wire...?? I would make the rookie assumption that voltage drop would apply to the solo panel as well.....allowing the solo panel to deliver a relatively similar ratio of amperage (maybe 2/10's of an amp)..??

                    Comment


                    • #12
                      Originally posted by tb144050 View Post


                      Very helpful insight. Is there a formula to calculate the voltage drop at 40ft, given the parameters of this setup? Even still, my newbie mind still does not understand why an expected paralled current of ~ 10-15amps (cloudy day, 3 panels) drops to 1.1 amp.......but I successfully receive 2.5amp from 1 panel on 10awg wire...?? I would make the rookie assumption that voltage drop would apply to the solo panel as well.....allowing the solo panel to deliver a relatively similar ratio of amperage (maybe 2/10's of an amp)..??
                      I agree that the voltage drop on the #10 for the 3 panels may be just one of the issues. I still think you have either a bad wiring connection or one of those panels is screwed up causing a major reduction in output. But if you measured it on a cloudy day more than likely none of the panels were producing a lot.

                      You might try hooking up each of the 4 panels to that single pair of wires (one at a time) to see what they produce at the end of the long run. That might show if you have a panel or wiring issue with the DIY 3 to 1 MC4 set up.
                      Last edited by SunEagle; 11-04-2016, 02:18 PM. Reason: updated post

                      Comment


                      • #13
                        >>>> Is there an electrical reason why a person cannot make their own 3-to-1 parrallel mc4 connections?
                        >> No. In fact those are available off the shelf.

                        Yes - But - More than 2 panels in parallel, should have protection devices (fuse or breaker) so that an array of good panels, can't ignite a single bad panel.
                        Using wood mounts is just adding fuel to the fire !

                        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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                        • #14
                          ill try to answer the replies but I'm a little short on time right now. Yes I am temporarily using wood Two By Twos for the mounTing until I move beyond the bench testing phase. where should I put the fuses and how many and also what size should the fuses be for these panels?

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                          • #15
                            Originally posted by tb144050 View Post
                            ill try to answer the replies but I'm a little short on time right now. Yes I am temporarily using wood Two By Twos for the mounTing until I move beyond the bench testing phase. where should I put the fuses and how many and also what size should the fuses be for these panels?
                            The fuses should be as close to the panel as possible ahead of the wire going to the charge controller.

                            Sometimes you can put all of the fuses in the same box like I did in the attached picture. It was built to handle up to 5 panels. My panels are ground located and the combiner box is right behind them.

                            The fuse size should be provided on the back of the panel. I am using 8 amp for each of my 80 & 90 watt panels.

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