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  • Maximising Solar charge controllers limits

    Hello,

    I am new here.

    I plan to order and have wired in series 3 x 240w (48-Cell) Jinko JKM240M-48 Panels rated at:

    26.1V (Vmp)
    9.20A (Imp)
    32.1V (Voc)


    Its a Portable setup and thus it will not be hard wired to my roof.

    I will run 50ft of 10AWG cabeling from my Panels to my Charge controller. I expect a voltage drop loss of +-1.46%

    I will wire these panels to a Victron 100v/50A Mppt Solar Controller - https://www.victronenergy.com/upload...-100-50-EN.pdf


    The questions I have are as follows:

    - Will my Solar Controller be able accept this array ?

    - I did the following maths below (based on all three in series @STC) is it correct?:

    32.1v x 3 = 96.3v - Based on this, am I safe to say that the voltage will not exceed my controllers limit here?

    26.1v x 3 = 78,3v
    78.3v - 1.46% = 77.16v - This is the voltage that will run down my 50ft run of 10AWG cabling and into my Charge Controller less the 1.46% loss.

    77.16v/13.6v (Absorption rate suitable for my battery bank) = 5.673 - This is the ratio I will need to multiply the Imp of my array which is 9.20A.

    9.20*5.673 = 52.19A - this is the Amperage my Solar Controller would theoretically output into my battery, however the solar controller can only put out 50A total.

    - If my charge controller is only 98% efficient does this mean that total amps to my battery should be 52.19A - 3% = 50.62A?

    - My battery bank is 2 x 12v 100AH AGM deep cycles connected in Parallel (200AH Capacity). Do I have too much panel for my relative to my Battery bank? I will boondock in my Camper for weeks at a time.

    Thank you,

    Michael

  • #2
    You made a mistake, a costly mistake. Do Not Use Prime Numbers of Panels. Exception is 1 and 3 if your controller is 150 VOC. With a Prime number like 3 forces you to wire all panels in either series or parallel. Your controller VOC is 100 volts, and 3 x 32.1 x 1.25 = 120 volts which is greater than 100 volt input limit. 2 of those panels in series is max limit.

    So now you are forced to wire all the panels in parallel which means you now need a combiner, fuses, and at 50 feet will now need larger wire, 4 AWG to be less than 3% loss. You only have a 50 amp controller and max input is roughly 650 watts before clipping. You can get away with that, but be aware you are shaving power off from a potential 720 watts.

    Additionally you should be using 6-volt batteries wired in series, at 50 amps of charge current they really need to be 400 to 500 AH cells. In parallel you are significantly shortening cycle life. Loose one panel wire them in series and you are back within normal charging limits. As of now too much panel wattage, and you are stuck with the batteries.

    Should have done your homework first and avoided all the problems. As for controller efficiency is power, not amps.
    Last edited by Sunking; 05-21-2018, 04:01 PM.
    MSEE, PE

    Comment


    • #3
      Originally posted by IntoTheWild View Post
      32.1v x 3 = 96.3v - Based on this, am I safe to say that the voltage will not exceed my controllers limit here?
      No. Voc is measured at STC (25 degrees C.) In colder temperatures (i.e. winter mornings) you will see much more than that.
      - If my charge controller is only 98% efficient does this mean that total amps to my battery should be 52.19A - 3% = 50.62A?
      You will see losses from:
      -wiring
      -controller (98% is a suspicious number; it's very hard to get that sort of efficiency under real world conditions)
      -heat. At midday the panels will be quite hot, and so voltage will decline.

      All that being said, the controller will limit output current to 50 amps or so, so you won't have to worry about too much power.

      Comment


      • #4
        Hi Sunking,

        Thanks for sharing your knowledge with me! I appreciate the prompt reply to!

        As for my solar equipment, nothing has been purchased or ordered yet.
        I figured I would ask all my questions here first.

        My camper was delivered with two new batteries wired in parallel by the previous owner so I am just going to live with this battery bank for the time being and rather spend my money on other upgrades.

        Originally posted by Sunking View Post
        In parallel you are significantly shortening cycle life.
        What brings you to this bit of information? Are you referring to unbalanced charging?

        I will make sure that my batteries wired in parallel optimally as per the picture below:

        Screen Shot 2018-05-22 at 12.22.52 AM.png

        Originally posted by Sunking View Post
        Additionally you should be using 6-volt batteries wired in series, at 50 amps of charge current they really need to be 400 to 500 AH cells.
        My current usage in the camper is VERY low. It is also a modern camper so all appliances are very efficient and they draw very low levels of currents. So for the foreseeable future my 200Ah battery bank will work for me.
        • What exactly is the rule of thumb for deciding the optimum amount of current charge for a battery bank? I do recall reading that 10% of the bank capacity as a ratio was the optimal number? Could you kindly give me some more insight?

        SO, with my current battery bank being 200AH and the fact that I wont be increasing its capacity in the near future, I think a 480w panel array (2 x 240w in series) is going to be more than adequate for my current needs (pun intended) and as you have suggest better suited to my battery bank. Am I on the right track here?

        Lastly I live in Cape Town, South Africa. Temperatures rarely drop below 0

        Comment


        • #5
          Hi Jflorey2,

          Just wanted to thank you for your input too.

          Can you share with me, using the information I have now settled on with my reply to Sunking, What my real world loses would be an more realistically what my numbers would look like please?

          If you could show me the maths behind your reply that would greatly help too.

          Thanks,

          Mike

          Comment


          • #6
            Originally posted by IntoTheWild View Post
            My camper was delivered with two new batteries wired in parallel by the previous owner so I am just going to live with this battery bank for the time being and rather spend my money on other upgrades.
            OK when replacement time comes, use 6-volt cells and wire in series.



            Originally posted by IntoTheWild View Post
            What brings you to this bit of information? Are you referring to unbalanced charging?

            I will make sure that my batteries wired in parallel optimally as per the picture below:
            40 years of professional experience working with all battery manufactures and sat on IEEE Battery Committee who writes the standards and practices. Unbalanced charging and discharging. That method is just a band aid and work around for when that is all you got. Like I said fix it when replacement time comes.

            Originally posted by IntoTheWild View Post
            What exactly is the rule of thumb for deciding the optimum amount of current charge for a battery bank? I do recall reading that 10% of the bank capacity as a ratio was the optimal number? Could you kindly give me some more insight?
            10 to 15% (C/10 to C/8) is a good rule of thumb but there are exceptions. Hybrid batteries can be both charged and discharge at higher rates than Deep Cycle batteries. Hybrids come with Marketing names like Golf Cart, Leisure, RV, Marine Deep Cycle, Wheel Chair, Trolling Motor, Electric Vehicle and the list goes on. The Hybrid tries to be both SLI and Deep Cycle battery. Never use a SLI battery. The trade off is cycle life for C-Rates. To get higher C-Rates, you give up cycle life.

            Originally posted by IntoTheWild View Post
            I think a 480w panel array (2 x 240w in series) is going to be more than adequate for my current needs (pun intended) and as you have suggest better suited to my battery bank. Am I on the right track here?
            That will work and 480 watts is a bit much for your batteries. That will put you at 40 amps charge current which suggest 400 AH battery. So you are charging at C/4 or 25%.

            Forget about Solar for the moment, an Electronic Battery Isolator is more important. It allows you to charge the batteries from the Alternator and 2 hour engine runt time wil generate more power than your panels can do in a couple of days.

            Originally posted by IntoTheWild View Post
            Lastly I live in Cape Town, South Africa. Temperatures rarely drop below 0
            So? First morning when you get down to 16 Celsius (60 F), Puff The Magic Dragon comes calling, and let's the Magic Smoke out of your controller. It does not take 0 degrees to do the damage. You are at the maximum limit at a warm 25 C, and just a few degrees below that you are over limit. You need 125% voltage cushion. For a 100 volt controller would be 100 / 1.25 = 80 volts maxim panel VOC @ 25C. That means no more than 2 panels in series. To grow to 3 panels you will need a 150 VOC 60 amp controller, even better a 80 amp controller to go to 1000 watts @ 12 volt battery. MPPT Controllers go up to 600 volts so you can use 14 AWG for for a long long distance saving you MONEY, Weight, and Power Loss.

            MSEE, PE

            Comment


            • #7
              Sunking,

              It seems no one can supply me with 48 Cell panel modules here.

              Thoughts on 1 x 60 cell module 300w for my current needs vs say 2 x 36 cell 150w modules ?

              Will be a mobile unit for placing in the sun once my Camper is parked in the shade.

              Which setup would my MTTP controller draw more power from or operate better with?

              M

              Comment


              • #8
                One thing for sure, the 2, 150 watt panels will draw a lot more money from your wallet than one 300 watt panel will.
                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                Comment


                • #9
                  Originally posted by littleharbor View Post
                  One thing for sure, the 2, 150 watt panels will draw a lot more money from your wallet than one 300 watt panel will.
                  I can buy wholesale for $0.50 per watt for the 150W panels and $0.42 per watt for the 300w panel. Neither her nor there in terms of price.

                  What I am more interested in are the pros and cons of the two options I presented in relation to mobile placement of the panels when Boondocking and then when traveling over bumpy roads etc.

                  And not to mention how an MPPT controller would work with one big panel vs two smaller panels.

                  Have you go any input on the above?

                  M

                  Comment


                  • #10
                    Great price for 12 volt panels. Brand?
                    I would think the 60 cell panel would be unwieldy to have to store and set up on a regular basis. You would need some kind of ballast or anchor to keep the wind from taking it for a ride. Of course that applies to the smaller panels as well. I lost a panel once to the wind gods in Baja.
                    Last edited by littleharbor; 05-23-2018, 01:07 PM.
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                    Comment


                    • #11
                      On a separate note do you think

                      Do you think I would pushing it if I rigged up two of these in series with a 100VOC controller:

                      Screen Shot 2018-05-23 at 7.32.12 PM.png
                      87.8 x 1.25 = 109.75VOC

                      But I think 25% may be a very safe margin of error.

                      Thoughts?




                      Comment


                      • #12
                        Originally posted by IntoTheWild View Post
                        Can you share with me, using the information I have now settled on with my reply to Sunking, What my real world loses would be an more realistically what my numbers would look like please?

                        If you could show me the maths behind your reply that would greatly help too.
                        Well, I can't give you your losses of course but I can give you the math for it.

                        First off, for solar, you will have to figure out actual power being generated. This varies due to a lot of factors (temperature, insolation, angle, weather) and you're not going to get a 100% accurate number here. 75 to 80% of STC rating in full noon sun is a good estimate there.

                        Next is wiring loss. This is pretty easy. Figure out how much resistance you'll have in the wiring (remember, both hot and return have to be figured in here.) Power loss is I^2R (I is current and R is resistance.) You can get resistance from a chart that shows AWG (wire size) vs resistance per foot. Voltage loss is I times R.

                        Next is inverter and controller losses. This is a little easier because these are usually in the user's manual. But beware - the manufacturer will give you the best possible efficiency number, taken at one operating point. The better manufacturers provide a graph showing loading (or current) vs efficiency. Use that graph; find your load and look up the efficiency that way.

                        Comment


                        • #13
                          Originally posted by Sunking View Post
                          So? First morning when you get down to 16 Celsius (60 F), Puff The Magic Dragon comes calling, and let's the Magic Smoke out of your controller. It does not take 0 degrees to do the damage. You are at the maximum limit at a warm 25 C, and just a few degrees below that you are over limit. You need 125% voltage cushion. For a 100 volt controller would be 100 / 1.25 = 80 volts maxim panel VOC @ 25C. That means no more than 2 panels in series. To grow to 3 panels you will need a 150 VOC 60 amp controller, even better a 80 amp controller to go to 1000 watts @ 12 volt battery. MPPT Controllers go up to 600 volts so you can use 14 AWG for for a long long distance saving you MONEY, Weight, and Power Loss.
                          Sunking Can you perhaps give some replies to my questions above?

                          Comment


                          • #14
                            Most of the "big" charge controllers will log in eprom memory, high voltage events. At the warranty threshold of 100V, maybe 102V will force it into shutdown, and 108V will fry the input stage. But exceeding the 100v threshold gets logged, and that voids the warranty. Midnight Solar will allow the kill voltage (per model, 150, 200, 250.....) to exceed the kill voltage by the battery voltage. So the 150V model, used in a 48V system, will gracefully survive 198V at the PV input. It does that at the expense of shutting down until the PV voltage returns to the safe voltage, so a cold morning will still cost you up to a couple hours of harvest till the panels heat 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

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