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  • Small Off Grid Setup Questions

    Hi All,

    I am looking to set up a small off grid solar system and would appreciate some advise and pointing to specific cables etc I might need.

    I have bought the following so far:

    Renogy 2pcs 100 Watt 12 Volt Monocrystalline Solar Panel (Compact Design) Ideal for Off Grid PV System on Motorhome, Caravan, Campervan or Boat

    12v 115AH Expedition Plus AGM Leisure Battery (EXP12-115)

    EPEVER Qaurora MPPT Solar Charge Controller Tracer AN Series 10A/20A/30A/40A with 12V/24V DC Automatically Identifying System Voltage(40A)

    I plan to set the 2 solar panels up in series producing 37.8V and 5.29 amps.

    I believe my MPPT solar charge controller is good for up to 100V input from solar panels.

    My question (sorry nubie question) is if the panels are operating in series at 37.8V then can this still be a 12V system on the battery? Does the fact I only have 1 12V battery mean that the battery is the deciding factor in the off grid systems voltage?

    I would appreciate it if anyone could advise (and provide links if possible) to the cabling that I would require to connect everything up and any fuses or circuit breakers I would need as I am struggling to understand this part.

    I plan to use this off grid system as an emergency backup to charge essential devices and provide some LED lighting.

    Any advise on the connectors that could be used to connect items to the solar charge controller (phone etc) so they can charge would also be highly appreciated.

    Many Thanks,

    Ben

  • #2
    Hello Slayer2k and welcome to Solar Panel Talk

    I will say that if you have a quality CC you will be able to charge your 12V battery with those two panels wired in series. The battery voltage will limit you to using 12V loads unless you use an inverter to generate AC power. You can also use a DC to DC converter to power loads that have a different voltage rating then your battery but that usually results in heavy losses due to the inefficiency of the converter.

    The cable sizes will depend on the amount of current they carry based on the load requirements. They should include over-current protection (fuse or circuit breaker) ahead of each wire run.

    Comment


    • #3
      As @SunEagle said, the system voltage will be determined by the batteries. Your MPPT charge controller can presumably reduce the 37 volts to the correct charging voltage. You will have less voltage loss and can use smaller wire by running a higher voltage, especially if your panels are some distance from the other equipment. . The question I have is whether or not it would be more efficient to parallel the panels? I don't know the answer, so that is just speculation on my part.
      Last edited by Ampster; 03-23-2020, 09:47 AM.

      Comment


      • #4
        Originally posted by Ampster View Post
        As @SunEagle said, the system voltage will be determined by the batteries. Your MPPT charge controller can presumably reduce the 37 volts to the correct charging voltage. You will have less voltage loss and can use smaller wire by running a higher voltage, especially if your panels are some distance from the other equipment. . The question I have is whether or not it would be more efficient to parallel the batteries? I don't know the answer, so that is just speculation on my part.
        With a quality MPPT type CC it doesn't really matter how the panels are wired but usually wiring them in series up to the maximum input voltage is more acceptable then wiring them in parallel to reduce wire size. But again with only two panels the OP will not have to worry about a combiner box with over-current protection for each parallel string.

        Comment


        • #5
          Originally posted by SunEagle View Post

          With a quality MPPT type CC it doesn't really matter how the panels are wired but usually wiring them in series up to the maximum input voltage is more acceptable then wiring them in parallel to reduce wire size. But again with only two panels the OP will not have to worry about a combiner box with over-current protection for each parallel string.
          Thanks that answers my question. I meant to say panels instead of batteries but you caught my drift.

          Comment


          • #6
            Originally posted by Ampster View Post

            Thanks that answers my question. I meant to say panels instead of batteries but you caught my drift.
            The usual break point of how panels should be wired is around 200watts. Depending on the battery voltage once you go above 200watts an MPPT is the better way to go. If you have say 2 x 90watt panels a PWM still works but also looses some of the amp generation.

            Again it all depends on what the person needs to charge their battery system and if quality equipment is worth the cost.

            Remember for MPPT, watts in = watts out. For PWM, amp in = amps out.
            Last edited by SunEagle; 03-23-2020, 10:11 AM. Reason: added last sentence

            Comment


            • #7
              Thanks for the replies everyone.

              What I am looking to understand in more detail is what fuses/circuit breakers and cabling options there are and if anyone could link to some examples that would be appreciated.

              I plan to put the 2 solar panels within 30 to 40 feet of the battery and plan to wire in series as I believe this means as you have stated I can use thinner wire.

              How can I work out what wire gauge I need and again any links would be appreciated to any examples of wiring.

              Can I buy the wires made up or do I need to buy a crimping kit etc?

              Thanks Again,

              Comment


              • #8
                There are a number of jumper cables available for solar equipment that already include a connector like the MC4 pre-terminated at each end. Most of the ones I have found are rated #10awg but be careful of the smaller and cheaper ones out there.

                With a series wired panel system it helps keep the voltage drop within the limits even at 40 feet while using that #10 wire. There are also inline fuses that can be added to protect that #10 wire.

                The wire between the charge controller and batteries will be determined by the CC rating and your DC load or AC inverter wattage rating. You will need an over-current device ahead of each wire between the CC and batteries along with the wires between your batteries and loads.

                Comment


                • #9
                  Thanks Sun Eagle,

                  I think I am getting there slowly

                  So with this schematic from my mppt controller:




                  I assume these mc4 cables are acceptable to connect to the series aligned solar panels to the mppt controller: https://www.amazon.co.uk/BougeRV-Ext...xpY2s9dHJ1ZQ==

                  Am I right in thinking that I need this in line fuse (Breaker in diagram above?) between the mppt controller and the Solar Panels?: https://www.amazon.co.uk/Renogy-Wate...5012830&sr=8-5

                  (15 amp as the 10 guage AWG can support a maximum of 15 amps?)

                  Do I need two of these according to the schematic above (one for positive cable from solar to mppt and one for negative cable to mppt)?

                  If so do I need to buy a different one for negative and positive or will the inline fuse fit both by turning the fuse holder around 180 degrees?

                  I assume if the above assumptions are correct then I can use a third one between the mppt controller and the loads? (again a 15 amp inline fuse?)
                  I want to be able to charge mobile phones, tablets and run some led lights for my loads (no inverter needed) so would I still need 10 awg for this or a different type of cable and connectors?
                  Can you please link to any that would be of use?

                  If my mppt contoller is 40 amps and the load is the sum of my charging items then this would be roughly (40+5(mobile phone)+5(mobile phone)+8(tablet)+10(Strip LEDs) ) so roughly 58 amps?

                  That would mean I would need a 4awg set of wires from the battery to the mppt controller as this supports up to 60amp with a minimum 75amp fuse (60x1.25amp as per teh schematic above)?

                  Im not sure if this is correct or I have it wrong and would appreciate any advise again,

                  Thanks for taking the time to help,


                  Comment


                  • #10
                    Most automotive style fuses, will melt the contacts and wires, because solar is long term, high power. Automotive gear is not designed for that. Perhaps the "MAXI" style of automotive blade fuses, will hold up.
                    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


                    • #11
                      Thanks all,

                      With the load output from the mppt controller I am trying to understand what my options are to charge multiple mobile phones and tablets and also an led light strip.

                      Is it a case of making up the cabling and connectors or can these be bought ready made?

                      Again, any advice appreciated,

                      Thanks,

                      Comment


                      • #12
                        One other question, can my 40Amp Solar Chrge Controller charge the battery at a lower amperage? I am aware that an AM battery should not be charged at more than 10% of its capacity. Do solar charge controllers adjust this automatically?

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