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  • #16
    Originally posted by Sunking View Post

    The only true statement you can make is one of math. A 800 watt panel with 65 amp controller will always produce As Much Or More Than a 800 watt Panel with a 50 amp controller under any condition. There is no circumstance in which 800 watts with a 50 amp controller ever gives an advantage. Most of the time in real application you get much less. That is not an opinion, that is a mathematical fact and a True Statement.

    What am I missing here? .
    A 65 A controller costs more, requires heavier wiring. If a 50 A gives you the vast majority of the same power and energy, and is enough current to support the battery, spending the extra on the 65 A is waste of money. My point is that if I'm on a budget, and have to choose between buying more panels or a bigger controller, i'll pick more panels every time. It is also a fact that an 800 W system on a 30 A controller will produce as much or more than a 400 W array (with the same orientation) on that same controller 100% of the time. If, after putting up more panels, additional money is available to upgrade the controller and get that incremental energy that would have been clipped, great. Going from 400 W to 600 W, the money is better spent on panels. Probably, at that point, I'd put money into the controller next, but it just depends on the site and actual production that I'm seeing.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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    • #17
      Originally posted by sensij View Post
      If a 50 A gives you the vast majority of the same power and energy,.
      That is a False Statement. There is no IF about it. Cannot happen. It is like saying a 50 HP engine gives you the same power and energy as a 65 hp engine does. It is not possible and leading you to a false conclusion. But hey if that is what you want to believe. OK with me, I am fine with it. But math and science is not on your side with this one.

      Your wire size argument does not hold water either. Both require a minimum 6 AWG up to 10 feet 1-way distance. Again leading you to the wrong conclusion.
      Last edited by Sunking; 06-01-2017, 10:09 PM.
      MSEE, PE

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      • #18
        Originally posted by Sunking View Post
        Your wire size argument does not hold water either. Both require a minimum 6 AWG up to 10 feet 1-way distance. Again leading you to the wrong conclusion.
        What the **** are you talking about? Read the words I wrote. 6 awg is necessary, heavier if longer than 10 ft.

        Edit:. Ok, I figured out what you were responding to. Yes, if comparing a 50 A cc and a 65 A cc on a 12 volt system, they take the same wire size... No cost difference there. That doesn't change the fact that the 65 A cc is probably more expensive, money wasted if the panels aren't capable of producing that much power due to actual irradiance and installation orientation.
        Last edited by sensij; 06-02-2017, 10:23 AM.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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        • #19
          Originally posted by Sunking View Post
          That is a False Statement. There is no IF about it. Cannot happen. It is like saying a 50 HP engine gives you the same power and energy as a 65 hp engine does. It is not possible and leading you to a false conclusion. But hey if that is what you want to believe. OK with me, I am fine with it. But math and science is not on your side with this one.
          I know you are not really this dumb. If the panel output only exceeds 50 A for 12 hours in a year, then yes, a 50 A charge controller can deliver the vast majority of the energy that would be delivered by a 65 A controller. Basic fractions, learned them in 3rd grade. How about you?
          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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          • #20
            Originally posted by sensij View Post

            I know you are not really this dumb. If the panel output only exceeds 50 A for 12 hours in a year, then yes, a 50 A charge controller can deliver the vast majority of the energy that would be delivered by a 65 A controller. Basic fractions, learned them in 3rd grade. How about you?
            We all have dumbass attacks. I learned fractions in Kindergarten. What took you so long? Did you go to public schools after 1975?

            Sensij I know the point you are driving at. I get it. But your assumptions are wrong. You are assuming the panel will spend most of its life at 750 W/m2 or less which is factually inaccurate. I agree if an 800 watt panel is exposed to 750 w/m2, the power will be 600 watts or less with either controler. But you are going miss out a couple of hours when irradiance is significantly higher before and afternoon. So to say both power and energy are the same is just plain false. 600 watts of power does not equal even 700 watts of power. Nor does 2400 watt hours of energy equal 2800 watt hours of energy on a 4 Sun Hour day.

            You can also loose the argument on pricing. You can get a mediocre Victron 50 amp cc for $300 and have to put up with limited 100 Voc which forces you to wire panels in parallel requiring more wire. Although just short of 65 amps, you can get top of the line 150 Voc Morningstar TS-MPPT-60 amp cc for less than $180 delivered and wire the panels in series gaining efficiency and cutting wire and hardware cost. So your cost savings can be shot to pieces.

            The wire between controller and battery is a non issue. You don't have any legs to stand on. Both require 6 AWG up to 10 feet and in an RV highly unlikely you need to go more than 10 feet. A couple more feet will not hurt.
            MSEE, PE

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            • #21
              Originally posted by Sunking View Post
              We all have dumbass attacks...

              Although just short of 65 amps, you can get top of the line 150 Voc Morningstar TS-MPPT-60 amp cc for less than $180 delivered and wire the panels in series gaining efficiency and cutting wire and hardware cost. So your cost savings can be shot to pieces.
              .
              Yep, you just linked a PWM controller.
              CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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              • #22
                Originally posted by Sunking View Post

                Sensij I know the point you are driving at. I get it. But your assumptions are wrong. You are assuming the panel will spend most of its life at 750 W/m2 or less which is factually inaccurate.
                Even at 940 W/m2, a good system still produces only about 84% of STC. I have an irradiance sensor mounted next to my array... here is the tabular data for the chart I posted from my actual PV system. The column on the right labeled V is actually horizontal irradiance in W/m2, just a quirk of PVOutput's interface that forces the V unit on it. The temperature in the 2nd column from the right is the measured rooftop temperature, showing that this wasn't an exceptionally hot day (which would depress power). The 3rd column from the right is the % of STC that is being produced in that instant, measured every 5 min.

                On that day, of the ~110 healthy San Diego systems that report into Team San Diego on PVOutput, mine was the 40th most productive. So yeah, there are systems that produce more, but mine is still showing up as somewhat better than average, and I think a reasonable example of "good" system output, especially for being 2 years old.
                data 1.JPG
                data 2.JPG
                data 3.JPG
                Last edited by sensij; 06-02-2017, 01:19 PM.
                CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                • #23
                  Originally posted by sensij View Post

                  Yep, you just linked a PWM controller.
                  Yep SK linked the wrong CC. That Morningstar does have a max DC input of 125V but is also about $400 less then the PWM version.

                  For the OP I would go with the MPPT 60A version. It will be a better investment.

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                  • #24
                    Originally posted by sensij View Post
                    Yep, you just linked a PWM controller.
                    My bad. Thanks. A 60 amp MS-MPPT-60 is around $500. As Sun Eagle said a 60 amp MPPT is a better investment because it is higher quality and with higher yields making it a better long term. You do not have to upgrade. I would take a $500 Morningstar over a $300 Victon any day of the week even if they were both 50 amps. .

                    You can stick to underperformance, and I will stick with meeting expectations. I am OK with that.
                    Last edited by Sunking; 06-02-2017, 01:25 PM.
                    MSEE, PE

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                    • #25
                      Originally posted by SunEagle View Post

                      Yep SK linked the wrong CC. That Morningstar does have a max DC input of 125V but is also about $400 less then the PWM version.

                      For the OP I would go with the MPPT 60A version. It will be a better investment.
                      That is exactly my point, If you can buy a 50 A CC for $300, or the 60 A for $531, and going with the 60 A doesn't offer a meaningful increase in charge energy because panels don't actually hit STC in the real world, the extra $231 (in this case) being spent on the bigger controller is wasted money.

                      That $231 will buy 400 W of panels. For the same money, I could put 1200 W of panels on a 50 A controller or 800 W on a 60 A. I assure you, the 1200 W system will take better care of the battery, even though it *appears* wasteful because on a good day, so much is clipped. On cloudier days, which are common in most parts of the country, the bigger array is much better for the battery.

                      If you want to say only Morningstar brand is "good enough" to use on a system, and Victron is not, that is a different argument, and one in which there are lots of Victron owners out there who might feel differently.
                      Last edited by sensij; 06-02-2017, 01:32 PM.
                      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                      • #26
                        Originally posted by sensij View Post

                        That is exactly my point, If you can buy a 50 A CC for $300, or the 60 A for $531, and going with the 60 A doesn't offer a meaningful increase in charge energy because panels don't actually hit STC in the real world, the extra $231 (in this case) being spent on the bigger controller is wasted money.

                        That $231 will buy 400 W of panels. For the same money, I could put 1200 W of panels on a 50 A controller or 800 W on a 60 A. I assure you, the 1200 W system will take better care of the battery, even though it *appears* wasteful because on a good day, so much is clipped. On cloudier days, which are common in most parts of the country, the bigger array is much better for the battery.

                        If you want to say only Morningstar brand is "good enough" to use on a system, and Victron is not, that is a different argument, and one in which there are lots of Victron owners out there who might feel differently.
                        I agree the decision to go with a Morningstar, Victron or brand X would be up to the person and their reasoning.

                        While I don't like to waste money I would prefer to spend more on a quality inverter with a higher amp rating up front because of the chance of wanting to enlarge my pv system. Spending less now may save money but if you have maxed out the CC and need more later you have to start from scratch and purchase a new bigger CC. To me that is a waste of money if I can no longer use a smaller CC.

                        Again it all falls down to what you want and what you need. Most people come to this forum asking for a large solar /battery system but do not have the money for it. Or others come with the question of how do they enlarge their system because it is under performing.

                        For the first group I try to explain that a solar /battery system is neither cheap or will save you money compared to grid power so unless they have the cash don't plan on going with a solar/battery system.

                        For the second group I would say that they did not do their homework to determine what the actually needed and now that they have purchase cheap equipment that is limited they need to start over and end up spending more then what they could have by engineering the system in the beginning.

                        It is hard to help people make the right choices when you really don't know what they really need.

                        For me and SK we feel that up sizing a system is the better way to go even if it costs more now because it will certainly cost more later.

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                        • #27
                          Sensij I have no problem over sizing panels up to a point. Form me that point is 10%, for you are going to 25%. OK fine if that is what you like to do.

                          Second point is I would never spec Victron equipment. I assume you are referring to Blue 100/50 controller? If so right in the specs maximum power input 700 watts. Ok that is a bit over 10%, but 800 is over the limits. Max Voc input is 100 Voc, and with the 320 watt panels you would want to wire them in parallel. In series you are pushing limits again you do not want to mess with. Yeah I know they say you can wire two 72 cell panels in series, but that is Swedes for you and that practice does not apply here. At least I will not do that. I sleep better knowing I am staying away from the cliff.

                          Lastly Victron equipment is just not the same quality as Morningstar, Midnite Solar Xantrex and a couple of other manufacturers out there. We just have to agree to disagree. You are willing to take a lot more risk than I would. Being a PE I am liable for all my work , and if something would happen, I could not defend myself to my peers who would judge me in a review.
                          Last edited by Sunking; 06-02-2017, 05:58 PM.
                          MSEE, PE

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                          • #28
                            Originally posted by Sunking View Post

                            Second point is I would never spec Victron equipment. I assume you are referring to Blue 100/50 controller? If so right in the specs maximum power input 700 watts. Ok that is a bit over 10%, but 800 is over the limits. Max Voc input is 100 Voc, and with the 320 watt panels you would want to wire them in parallel. In series you are pushing limits again you do not want to mess with. Yeah I know they say you can wire two 72 cell panels in series, but that is Swedes for you and that practice does not apply here. At least I will not do that. I sleep better knowing I am staying away from the cliff.

                            Lastly Victron equipment is just not the same quality as Morningstar, Midnite Solar Xantrex and a couple of other manufacturers out there. We just have to agree to disagree. You are willing to take a lot more risk than I would. Being a PE I am liable for all my work , and if something would happen, I could not defend myself to my peers who would judge me in a review.
                            I think it is ok to differentiate between the over-design required in a professional environment, and the "good enough" design on a budget that works for the average guy. I don't cut corners on safety, ever, and am fine to just agree to disagree on how to cost-effectively optimize performance. It is frustrating when you declare a combination as strictly incompatible, when in fact there can be good reasons for over-paneling away from the rules of thumbs you normally use.

                            The Victron isn't a great choice for over-paneling since it is limited to 100 Voc, but it serves the purpose here. I don't see a "max power input" anywhere in the specs. What I see is a "nominal power", basically telling you how much PV it takes to max out the 50 A. There is a note that states "if more PV power is connected, the controller will limit input power". This is exactly the condition that we want... by getting enough PV power on there that we get clipping, in real world conditions (not STC), we know we are fully utilizing the charge controllers capability, and haven't over-bought capability we don't need. Yes, for me, in off-grid systems that usually means planning 25% more PV power than the STC rating suggests can be handled, but I'd even support more than that in some cases. Many case studies in deficit charging could have been avoided with just a few more panels so that cloudy days can be more productive, and not limiting the array to what STC ratings say would max out a charge controller... conditions never achieved in the real world.

                            The *hard* limits for any decent mppt controller are the Voc and the Isc. As long as the array fits within those limits, I would not immediately judge it to be incompatible.

                            For 12 V, the 800 W on a 30 A controller that the OP asked about is getting excessive, but if the panels aren't at a great orientation, or are partially shaded, or the weather is predominantly cloudy, even that design may be defendable. Again, the frustrating point for me is that I think we should be asking those questions, while you and SunEagle always seem to jump to the immediate conclusion that a bigger charge controller is needed, even when for all practical purposes, it won't actually deliver enough additional energy to justify the cost.
                            victron.JPG
                            CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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                            • #29
                              Sensij first i never said what you propose is dangerous. So let's get that straight right now. I said you are pushing the electrical limits of the equipment and the two limits in the spec are Voc and Isc. I will ignore Isc since it does not factor into this discussion or being tested to the limits of 60 amps INPUT.

                              Voc is a number you want to stay away from. Not because it is a fire hazard, but because it is a Stress to semiconductors. Tubes are brutes, you can over voltage them all day long. Semiconductors are extremely sensitive to voltage, and over current. Current is not the issue here. One of the main advantages of using MPPT is so you can use high voltages. You know the benefits so enough of that. 72 cell panels Voc as you know is 45 to 47 volts. If you apply the minimal temp comp of 125% takes the 72 cell panel over 50 volts eliminating two panels in series. You have shot yourself in the foot wiring them in parallel.

                              As for over powering. Like I said I can see 10 %, you have no problem at 25%. The specs say the controller is rated for 600 watts, but can go to 720 Watts. OK by me, but 800 is greater than 720. I don't know how to make it any clearer, you are pushing the limits to far over the line of acceptable practices. If not for that alone, you would void any warranty doing that. I cannot tel you how many jobs I have declined because the client asked me to push the limits. I will not do it and send them packing. I would much rather folks spend of few more percentage points on equipment I know will perform at optimum conditions under worse case circumstances.

                              So how would I use a this 50 amp controller. Instead of spending the money on 800 watts of panels, I would save them $300 using 600 watts, and use $100 of that $300 saved for a good Electronic Battery Isolator giving them an alternate source of power they will need, not to mention do the majority of the real battery charging all without even thinking or worrying about how much power they use. Plenty more where that came from by just starting the engine. Hell you know as well as I do if you drive every 2 or 3 days, you do not need the panels. All they really do is give you a few extra days. before you have to fully recharge or risk ruining your batteries. So the way I see it my way is less expensive and way more robust with redundancy. That is an easy sell.
                              MSEE, PE

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