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  • #31
    Originally posted by Tobym View Post
    Yep I get that it's 4.86a so with 4 of them it means 50a into battery. Ps say I have 2 12v batteries I assume that's 25a amp in each not 50 into each
    This is where you are getting lost. You are not specifying Charge Controller Type or battery voltage.

    With PWM Input Current = Output Current. If you were to use 4 of those those panels in parallel on a 12 volt battery would deliver a max charge current of 4 x 4.86 amps = 19.44 amps or just 19.44 amps x 12 volts = 233 watt out of 680 watt input.

    With MPPT Output Current = Panel Wattage / Battery Voltage. So if you used those same 4 panels on a 12 volt battery (makes no difference if they are series or parallel) will deliver [4 x 170 watts] / 12 volts = 56 amps.

    Is 56 = 19.44 ?

    You had better know what you are doing.
    MSEE, PE

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    • #32
      Oh ok I'm going to use a mppt cc with 12v batteries so 56a but how does that distribute into say 2x 12v batteries wired in parallel so as a 12v system. Thanks Toby

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      • #33
        So it should be a 12v 60a mppt cc

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        • #34
          Originally posted by Tobym View Post
          Oh ok I'm going to use a mppt cc with 12v batteries so 56a but how does that distribute into say 2x 12v batteries wired in parallel so as a 12v system. Thanks Toby
          Divides to 28 amps per string. You do not want to parallel batteries very bad idea.
          MSEE, PE

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          • #35
            Originally posted by Tobym View Post
            So it should be a 12v 60a mppt cc
            Yep.
            MSEE, PE

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            • #36
              Poss wrong terminology I mean so the stay I a 12v configuration

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              • #37
                Originally posted by Tobym View Post
                Poss wrong terminology I mean so the stay I a 12v configuration
                No misunderstanding. You clearly said:

                2x 12v batteries wired in parallel so as a 12v system
                Which is a mistake. For example if those 12 volt batteries are 100 AH, with two in parallel makes them 12 volts @ 200 AH. Where you should use 2-6 volt 200 AH batteries wired in series to get 12 volts @ 200 AH. That mistake will cost you roughly 50% battery life, so instead of replacing batteries ever 3 years, now every 1.5 years. It is your money, not mine.
                MSEE, PE

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                • #38
                  Oh cool yep that was a mistake then. I didn't realise that about the parallel thing ill make sure I 6v wen I buy batteries so if I want 400ah I will need 2 200ah 6v batteries or would I have to get 6 70 ah 2vand get 420 ah or is there a way of using 6 v 100ah batteries. By the way why does it half the life of the batteries. Toby

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                  • #39
                    I'm looking at auto recognition mppt cc and the description says this
                    for 12v or 24v solar system, pls note 24v solar panel only can charge 24v battery, it can not charge 12v battery
                    It depends the solar panel not the regulator, there is not any regulator can make 24v solar panel charge 12v battery.

                    Is this true if so I'm screwed anyway as my panels are 35v

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                    • #40
                      Originally posted by Tobym View Post
                      I'm looking at auto recognition mppt cc and the description says this
                      for 12v or 24v solar system, pls note 24v solar panel only can charge 24v battery, it can not charge 12v battery
                      It depends the solar panel not the regulator, there is not any regulator can make 24v solar panel charge 12v battery.

                      Is this true if so I'm screwed anyway as my panels are 35v
                      You are looking at crap controllers. Any decent controller can run up to 150 Voc input on a 12 volt battery. Some can run up to 600 Voc input.
                      MSEE, PE

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                      • #41
                        Originally posted by Tobym View Post
                        Oh cool yep that was a mistake then. I didn't realise that about the parallel thing ill make sure I 6v wen I buy batteries so if I want 400ah I will need 2 200ah 6v batteries or would I have to get 6 70 ah 2vand get 420 ah or is there a way of using 6 v 100ah batteries. By the way why does it half the life of the batteries. Toby
                        No you do not understand parallel and series work.

                        Series voltage and power adds
                        Parallel current and power adds.
                        MSEE, PE

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                        • #42
                          Originally posted by Tobym View Post
                          Is this true if so I'm screwed anyway as my panels are 35v
                          You are screwed, but not from your panels and controllers. When you realize how much money it is going to cost you to generate 10 cents worth of electricity per day, and constant battery replacement cost, you will know you have screwed yourself big time. Instead of paying that mean ole POCO 10-cents per Kwh, you will now be paying that friendly green energy dealer some $2 Kwh for those lights you take off grid. That Green Dealer and I think you very much for making us rich Just think both of you will be tickled pink, Can't beat a scam like that huh?

                          Just like going to Vegas. You get robbed at the tables, over charged for everything, then come home and tell everyone what a good time you had and cannot wait to go back and do it again. It is pure genius I am telling you.
                          MSEE, PE

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                          • #43
                            I have always believed that I did but it turns out that its a deeper subject than I knew. Thanks for your help. It's so great to speak to an obvious authority on this subject.

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                            • #44
                              Toby all I am trying to do is to make you stop and do some cost analysis. I will give you the 10 second analysis. Anything you take off-grid will cost you 10 times more for power vs buying it from th ePower Company the rest of your life. Batteries and battery replacement cost big bucks.

                              You said back in post 4 or so you determined you would use about 500 watt hours per day for lighting after you change out all fixtures with LED's. I think you underestimate that value but let's run with it because the end result is the same. First point in your area I assume you pay the POCO about 11-cents per Kwh. So 500 wh is 5.5 cents per day of electricity. [.5 Kwh x $0.11 Kwh = $0.055] With me so far?

                              So look at battery cost and only battery cost alone, nothing else. To give you 500 wh off a battery requires a 2.5 Kwh capacity battery. At 12 volts that is 2500 wh / 12 volts = 208 AH @ 12 volts. Now we go shopping for batteries and we find out a 2 year battery cost $100/Kwh and a 5 year battery cost $220/Kwh. So the $220 Kwh is the best deal, like it or not the numbers do not lie.

                              So we opt for the five year battery so it cost you 2.5 Kwh x $220/Kwh $550. In 5 years it will cost more. OK here is where you crunch the numbers. In 5 years or 1825 days you use .5 Kwh x 1825 days = 912.5 Kwh. Now it is time to buy a new battery. So how much did each Kwh cost you in battery cost?

                              Well that is real easy to figure out $550 / 912.5 Kwh = $0.602 Kwh. I say ouch if the mean ole POCO only charges me $0.11 Kwh. That is roughly 6 times more than necessary.

                              What would you say?

                              I hope you did not choose that 2 year Walmart battery because it gets worse. In 2 years the battery will provide 730 days x .5 Kwh = 365 Kwh. The battery cost 2.5 x $100 = $250. Kwh cost are $250 / 365 Kwh = $0.685 Kwh

                              Hope that helps shine some light on things. Don't forget all that other equipment cost like panels, charge controllers wiring connectors, hardware, test equipment, water, ect. You also get a new part time job 7-days a week monitoring the system and fussing with consumption. Your kids will love that.
                              MSEE, PE

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                              • #45
                                Originally posted by Tobym View Post
                                Im a bit confused my panels are 170w and35v is that correct the 50a
                                This may make you a bit more confused.

                                680 watts/ 12 volts = 56.67 amps
                                In the real world, specifically on your system that we initially designed for a 30% DOD, you do not divide the watts by 12 because your batteries are not deeply discharged and an Mppt controller will not put out 12v but maybe closer to 14v to be able to charge the battery.
                                680/14=48.57amps or approximately 50A.
                                You get 48 amps or 56 amps, your options for a CC is the 60A or 80A model.

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