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  • Help sizing charge controller

    Hey guys, very informative post.
    I live in Kenya and I'm working on almost the same system but mine will be a 12V system (most of my appliances are 12V) or would you advice otherwise? . For now I only got the panels, three (3) 265w panels, I'm thinking of going with 150AH batteries...however, I'm not sure which is the best size MPPT in amperage I should use. The panels specs are:
    Pmax - 265w
    Vmp - 31.4v
    Imp - 8.44A
    Voc - 38.6v
    Isc - 9.03A
    Maximum system voltage - 1000VDC
    maximum series fuse rating - 15A

    Regards.

  • #2
    If the 150 Ah are FLA, a 20 A charge controller is about as much as you can use. More than that, and you would be at risk of overcharging your batteries, especially since you have so much PV wattage available (60 A at STC, assuming good orientation) of the panels.

    If the 150 Ah are AGM, a 40 A charge controller would be good.

    In either case you are still over-paneled, so you would need to make sure your mppt controller will properly limit the output current to the controllers rating. Some very inexpensive models may not.

    If you can go up to 230 Ah FLA, you can get a 30 A controller.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #3
      Thanks Sensij for the quick reply,
      No, I dont intend on getting FLA batteries, I can get a 200 Ah AGM battery to start with, then upgrade later if need be. Will that still work with the 40 A MPPT controller?

      My aim is to make maximum use of the panels I have and
      I've been going through earlier posts here and I read experts NOT recommending 12v system, so considering the panels I already have, I'm I better off going 24v system with an inverter or should I stick to my 12v system without an inverter? Which best way would you recommend?

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      • #4
        your 3 panels would give you 56 amps into a 12V battery, or 28a into a 24v battery - using a good quality MPPT controller, and well aimed, un-shaded panels.

        It's your choice, you say you have an investment in 12V appliances already, so maybe in your case, it's a reason to stick with 12V.

        For 12V, 400ah of battery would be a good match for the panel size. But this is backwards, you generally size the battery to run your loads for 3 or 4 days, and then configure solar to provide proper charging to the batteries. If you run 400ah of batteries flat every night, they will not last very long and seldom be properly charged.
        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
          At 12 volts and 800 watts of panels you have no room for growth with a 60 amp controller. Additionally 12 volt systems are more expensive than 24 and 48 volt systems. In Kenya you have excellent conditions with a minimum 5 Sun Hour day. With 795 watts of panels you can easily harvest 3 kWh of usable power in a day, and that would require a 12 volt 1000 AH battery. With a 12 volt 200 AH battery you need to loose 2 panels and use a 20 amp minimum controller with no place or room to grow.

          Smart money is to go with 24 volts. Initially you would only need a 30 amp controller at 24 volts, but that would leave you no room for future growth. Smart money initially is a 60 or 80 Amp Controller with a 24 volt 400 AH minimum battery. With that you can use up to 2.4 kWh per day or 5 times more than what Sensij just told you, and what you planned.

          You do not want or need an AGM battery. They cost twice as much and only last half as long as a FLA battery making them 400% higher cost. With a 24 volt 400 AH battery you can use up to 2 to 2.2 kWh per day. AGM has applications in solar but they need to be justified for the expense. Some justifications are:
          • Extremely cold climates where temps drop to -40.
          • Mobile applications where spills are unacceptable.
          • Very high charge and discharge rates are encountered.

          As Mike said you went about this the wrong way, and if you are married to 12 volts, maximum power at 12 volts is 1000 watts with an 80 amp controller. Th eproper way to design is to determine your daily watt hour usage. Batteries have minimum and maximum charge requirements. With 800 watts of panels, dictates minimum and maximum charge controller and battery requirements. with 800 watts of panels operating at 12 volt battery minimum requirements are a 60 amp controller and a 12 volt 500 AH FLA battery or 250 AH AGM battery and both those batteries cost the same. Consequently with 800 watts of panels and a 60 amp controller would be the maximum a 60 amp controller can handle, so no room for growth.

          You are trapping yourself because you went about this the wrong way. You bought panels and hoped it would work out.
          Last edited by Sunking; 01-07-2018, 02:31 PM.
          MSEE, PE

          Comment


          • #6
            Thank you Sunking for the detailed reply.
            As I'm not willing to throw away any of my panels and I can see that a 12v system might end up more costly for me, let me say that I'm flexible and am willing to go 24v, I understand that this will need me to get an inverter so as to use AC power on my appliances.
            The question is, will two 12v 150 Ah AGM batteries in series be ideal and how much in Amperage for the MPPT controller will I need?

            Comment


            • #7
              Thanks Sunking, I think that answers my question, now I know its smart to go 24v considering my panels wattage and that I need atleast 400Ah battery bank and a 60Amp MPPT controller...
              One last question, whats the maximum size of inverter can I use in my setup, I know this will depend mostly on my load, but whats the limit for my setup?
              Last edited by cmutwiwa; 01-07-2018, 04:50 PM.

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              • #8
                Thanks guys, I guess I will have to go with a 24v system and follow the guidelines given above.

                Comment


                • #9
                  Originally posted by cmutwiwa View Post
                  Thanks Sunking, I think that answers my question, now I know its smart to go 24v considering my panels wattage and that I need atleast 400Ah battery bank and a 60Amp MPPT controller...
                  One last question, whats the maximum size of inverter can I use in my setup, I know this will depend mostly on my load, but whats the limit for my setup?
                  You are welcome.

                  Ideally you normally do not want your Inverter to be any larger than your panel wattage using FLA batteries. That does not mean the Inverter should be as large as panel wattage. You only size the Inverter for maximum connected load that will be on at the same time. Once you figure that out and say the calculation is 800 watts, divide that by .85 and you come up with roughly 1000 watts. The reason for doing this is two fold.

                  1. Inverters are most efficient when running near maximum power.
                  2. If you recall I said batteries have minimum and maximum charge and discharge rates. For FLA batteries this limit is roughly C/8 for a true deep cycle, and some can discharge at C/6 where C = the AH capacity. So if you have say a 400 AH battery max discharge current would be 400/6 = 67 amps and at 24 volts x 67 amps = 1600 watts max inverter size so you would shop for 1500 watts or less. If everything was designed within limits, your panel wattage would also be roughly 1500 watts.

                  This is where AGM can be used because they can tolerate higher charge and discharge rates of C/4 to C/2 so that same 400 AH battery could power a 2400 to 4800 watt Inverter. But doing so is really going to mess with daily Watt Hours and Peukert Law. Think about that for a minute. A 24 volt 400 AH battery can only supply you with roughly 2400 watt hours per day. If you had say a 3000 watt load, Peukert Law would limit you to about 1800 watt hours or 40 minutes run time out of a 24 hour day.

                  So be realistic and do not over size your Inverter and do not take it to the limit.

                  MSEE, PE

                  Comment


                  • #10
                    Originally posted by Sunking View Post

                    This is where AGM can be used because they can tolerate higher charge and discharge rates of C/4 to C/2 so that same 400 AH battery could power a 2400 to 4800 watt Inverter. But doing so is really going to mess with daily Watt Hours and Peukert Law. Think about that for a minute. A 24 volt 400 AH battery can only supply you with roughly 2400 watt hours per day. If you had say a 3000 watt load, Peukert Law would limit you to about 1800 watt hours or 40 minutes run time out of a 24 hour day.

                    So be realistic and do not over size your Inverter and do not take it to the limit.
                    Thank you again Sunking, I really dont think I will use that much wattage, considering its mostly for lighting, TV & Radio.
                    I was looking at the MPPT controllers on eBay and came across one with this setup diagram, and I was wondering can the DC output on the controller power 12v light bulbs when the system is a 24v? may be that question doesnt make sense or it answers itself but I really need to be sure whether I will need to power the bulbs off the inverter output so I can acquire AC bulbs.
                    Attached Files

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                    • #11
                      Also...should I wire the panels in series or in parallel?

                      Comment


                      • #12
                        Originally posted by cmutwiwa View Post
                        Also...should I wire the panels in series or in parallel?
                        Assuming the controller you select has 150 V max input, put all three panels in series.

                        I would also suggest that before you going spending lots of money on the big battery and charge controller it sounds like you are considering, take some time instead to figure out how much power and energy you really need. There is no reason to oversize that part of the system if your loads don't require it, regardless of how much PV power you have.
                        Last edited by sensij; 01-11-2018, 11:03 AM.
                        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                        Comment


                        • #13
                          Originally posted by cmutwiwa View Post

                          Thank you again Sunking, I really dont think I will use that much wattage, considering its mostly for lighting, TV & Radio.
                          I was looking at the MPPT controllers on eBay and came across one with this setup diagram, and I was wondering can the DC output on the controller power 12v light bulbs when the system is a 24v? may be that question doesnt make sense or it answers itself but I really need to be sure whether I will need to power the bulbs off the inverter output so I can acquire AC bulbs.
                          Correct, you can not power 12 V loads directly from a 24 V battery. If your loads are *all* 12 V, and the only reason you are considering an inverter is because of the 24 V battery, you would be better off just sticking with a 12 V system.
                          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                          Comment


                          • #14
                            Max Voc. for a 12 volt system with the cc shown is 80 volts, only 105 for 24 volt system. Although the controller apparently can tolerate a max voltage of 190 volts.
                            Tried posting stats from their pages but it turns into some other text when submitted.
                            Last edited by littleharbor; 01-11-2018, 11:42 AM.
                            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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                            • #15
                              Originally posted by sensij View Post

                              Correct, you can not power 12 V loads directly from a 24 V battery. If your loads are *all* 12 V, and the only reason you are considering an inverter is because of the 24 V battery, you would be better off just sticking with a 12 V system.
                              Thanks Sensij, yes right now all loads are 12V, however this has been a limitation, I need to power a PC mostly during the day, so changing the lighting to accommodate the 24V system is an expense am willing to incur. I've read on other post here that its not a good idea to connect the panels in parallel since this will increase the current hence more cost in wiring and high power loss, so I think it will be better off doing it in series like you say.

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