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Charge controller and battery bank size recommendations for 860w of PV on Sprinter

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  • Charge controller and battery bank size recommendations for 860w of PV on Sprinter

    Hey folks,
    Sprinter build is getting started. I can source some 215w sunpower panels (but I'd totally go for some 345/360/370w if anyone has a source for Sunpower modules). With a custom racking system, I can squeeze 4 of them up there. Panels are a few years old, but specs are:
    SPR-215-WHT-U
    Peak Power 215W
    Voltage 39.8V
    5.4A current
    Open Circuit Voltage 48.3V
    Short Circuit Current 5.8A
    My draws are as follows:
    An ARB 47q running as a fridge
    An Engel 84q running as a freezer as soon as the new models come out
    A Maxair fan, and another as-of-yet-undetermined fan for air circulation
    Occasional night time use of a 40" TV
    Occasional night time use of a kinda thirsty (250-300w or so) gaming laptop
    Onboard compressor
    Device charging
    interior lighting
    microwave and possible AC use, but with a generator running.
    So, My questions are as follows:
    How big of an AGM bank can I get? Lithium still doesn't seem worth it right now. Especially after dropping so much dough on the sprinter.
    What controller or controllers should I use? My last rig had a single 310w panel so that was easy. I would like a controller that is good and can do lithium chemistry in the future when I upgrade battery banks. I have a midnite solar classic kid and it's...weird. A controller that allows extra current to go to an accessory would be nice, but not necessary.
    What's a good battery monitor? I've heard that Victron monitors are good. I still haven't got the whiz bang jr working for the Midnite Solar, and it's kind of annoying.
    I'll probably use a Samlex ACR-160 between the bank and the starter, unless you guys think it's putting too much strain on my stock alternator. What would be a good alternative? A DC-DC charger? Open to any suggestions here.
    Do you guys think it's overkill on the modules? I was shooting for a lot of input so I could potentially run AC during the day, but that seems kind of impossible, so minus that, do I need 860, would I be OK with 645? I had 310W on my old rig, and it couldn't keep up with my laptop and freezer running in the summer (though the freezer was a fairly inefficient Whynter 85qt) It also felt like my bank (2x 225AH Crown 6V batteries) dipped in voltage kinda quickly when the sun was down and I was running the laptop.
    Cheers,
    Alex

  • #2
    I am not going to give you answers, but I will tell you how to figure it out.

    MPPT Controller Size in amps = Panel Wattage / Battery Voltage
    Battery AH = 10 x Battery Charge Amps

    Example if you have 800 watts of panels and run 12 volt battery.

    800 / 12 = 66 Amps or a 65 amp minimum charge controller.

    Battery = 600 to 700 AH.
    MSEE, PE

    Comment


    • #3
      Hey sunking. Based on your recommendations, I'm passing on lithium this time around.
      Anyway, I appreciate you taking the time to explain this, but it's thrown a bit of a monkey wrench in my works. I thought I could wire in series or parallel to keep my voltage or amps down. As in, if I wired the whole thing in series, I would have max 5.8A and ~200V for 4 panels. If I did them all in parallel I would have 48.5V and ~24A. A 30A controller is way more palatable than an 80A one if I do 860W/12V=~72A.
      What am I missing?

      Comment


      • #4
        But you are eventually ending up at 12v for the house battery, and charge controllers are rated for output amps, regardless of the input. Most of the better controllers have a PV voltage limit of 150V, that you must never exceed, so designing a string for 100v is usually pretty safe.
        60A @ 12V is 720watts, so you could go up to about 1,000w in panels, and not max things out, unless you park on the equator, or on a 30degree hill, to get perfect panel alignment.
        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
          My current vehicle has a Midnite solar classic kid and a 310w panel. I don't think I've ever seen the thing output more than 16A. It's bananas to think I need to worry about almost 5x that amperage with less than 3x the wattage.

          I was planning on designing a tilting mechanism to maximize collection, especially in the winter months (I'm in Southern California). Also, I was think about the possibility that I find the larger output sunpower panels down the line, and buying a controller that can handle up to 1110W.

          But it seems that 100A controllers are much more scarce. What do you guys think about the outback power flex max 100a charger? Or magnum? I can't find a Morningstar rated over 60a.

          EDIT-That outback doesn't work at 12v. Dammit.

          My field season is starting soon, and I'd reaaaalllllyyy like to be lined out by then, so I'm forced to ask for lots of help and make quick decisions.

          I appreciate you guys answering all my questions.
          Last edited by Withalligators; 03-14-2018, 05:52 PM.

          Comment


          • #6
            Can I run a 24V battery bank, run the fridge/freezer/compressor off that, and use a step down converter to run my fans/lights/USB charging stuff/400W pure since inverter off of that? This would half my inverter and cabling cost (hyperbole, but you get what I mean), or is it just not worth the cost savings?

            Comment


            • #7
              Are 24v inverts running at half the loss? Is an 800w inverter as efficient at 24v as a 400w inverter at 12v?

              After a bunch of searching, I can find everything I want at 24v except exhaust fans and decent interior LEDs. If I can get better inverter efficiency, and save on cabling and a controller, I may consider 24v.

              Actually, what about charging a 24v bank off of a 12v alternator, and topping off the starter with solar when the bank is getting high current? This seems like the crux.

              Comment


              • #8
                Originally posted by Withalligators View Post
                Anyway, I appreciate you taking the time to explain this, but it's thrown a bit of a monkey wrench in my works. I thought I could wire in series or parallel to keep my voltage or amps down. As in, if I wired the whole thing in series, I would have max 5.8A and ~200V for 4 panels. If I did them all in parallel I would have 48.5V and ~24A. A 30A controller is way more palatable than an 80A one if I do 860W/12V=~72A.
                What am I missing?
                Simple math

                Watt Hours = Battery Voltage x Amp Hours
                Amp Hours = Watt Hours / Battery Voltage

                So lets say you need a battery capacity of 2400 watt hours. What is the capacity required at 12, 24 and 48 volts

                2400 watt hours = 12 volts x 200 AH
                2400 watt hours = 24 volts x 100AH
                2400 watt hours = 48 volts x 50 AH

                Lots of ways to build the 2400 watt hour battery at any of these voltages. Example you could use 4 x 12 volt 50 AH batteries. To do any of the three configurations.

                4P = 12 volts @ 200 AH
                2S2P = 24 volts @ 100 AH
                4S = 48 volts @ 50 AH

                However you would only use 50 AH batteries to make the 48 volt battery. You would not use them for 12 or 24 volts. If you need 12 volts @ 200 AH, then you buy 200 AH batteries like 2 x 6-volt golf cart batteries rated at 200 AH and wire them in series.

                Now go back to the first formula I gave you.

                Charge Amps = Panel Wattage / Battery Voltage.

                1000 watts / 12 volts = 84 amps
                1000 watts / 24 volts = 42 amps
                1000 watts / 48 volts = 21 amps.

                Seeing a pattern?





                Last edited by Sunking; 03-14-2018, 07:58 PM.
                MSEE, PE

                Comment


                • #9
                  If you are using an Inverter,, you can run battery voltage at whatever you want. Higher is better. Again simple math and this math will scream at your wallet. With a 80 amp controller you panel wattage limited by battery voltage.

                  1000 Watts @ 12 volts
                  2000 watts @ 24 volts
                  4000 watts @ 48 volts.

                  So if you have 1000 watts of panels which is more expensive

                  80 amp controller for 12 volt system
                  40 amp controller for 24 volt system
                  or
                  20 amp controller for 48 volt system.

                  ITS EASY MATH.
                  MSEE, PE

                  Comment


                  • #10
                    My question about inverters was more about efficiency. My understanding is such that at 12v to 120v, there is about a 10% loss to inverter size. So, my 330w laptop on a 400w inverter is actually using 330w + 40w. First off, is that true?

                    This is why I have a number of inverters. Try and match usage of commonly used items to maximize efficiency.

                    But I can't find any small inverters that work on 24v. They're all huge. But, at 24v, is there half as much loss to the inverter? ie ~5%? If so, it would still be a 40w cost to using an 800w inverter at 24v? Or am I going to be throwing away 80w on an 800w inverter at 24v? This is something I've wondered.

                    Anyway. Charging off the alternator with a 24v bank? How, DC-DC charger?

                    What about using step down converters from decent companies like Samlex for the 12v stuff? None of it is high draw. Or does the inherent inefficiency of step down converters mean might as well use 120 stuff off an inverter as loss will similar?
                    ​​

                    Comment


                    • #11
                      Inverter input (DC) voltage is only a minor contributor to efficiency. Quality of design is a major factor (Moringstar suresine 300)

                      Size of inverter is also a large factor, 5% loss in a 300w controller is much less than 5% of a 3,000w controller. Keeping all the big electronics warmed up eats power.

                      The PT-100 looks to be a decent product, I installed one, it went well, and the connections were well laid out
                      http://www.magnum-dimensions.com/pt-...rge-controller
                      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


                      • #12
                        What do you guys think about the Victron stuff? They have a bunch of 150/85 controllers that are rated for 1200W input. If I wire 2 pairs in series, I'd never exceed that, even with 3 x 370w panels (if I ever find them).

                        https://www.victronenergy.com/solar-charge-controllers

                        There are a few variations, I'm not sure which is best for my setup. The three options are the Bluesolar MPPT 150/85, SmartSolar 150/85, and then a different Bluesolar unit (which looks like an outdoor unit not applicable to me.

                        Which would you guys prefer? Bluesolar or Smartsolar? I can't find any real difference, but I can find the Smartsolar easier, and it looks more premium, whatever that's worth.

                        Comment


                        • #13
                          OK, I'm think I'm going to go with the Smartsolar 150/85-MC4. https://www.victronenergy.com/solar-...150-85-150-100

                          How do I wire it all up properly?

                          I think I'll wire it in 2 pairs in series, running in parallel. Is that correct?

                          Do I need a breaker on each positive lead? Even between panels? Or each series? Or just one coming into the controller, between the controller and batteries, and between the alternator and batteries? The data sheet for the panel has a 15A series fuse rating so I'll have one inline for each series.

                          What size should the breakers be?

                          What am I missing? I'm doing so many projects at once, I'm worried I'm going to screw something up with my old and addled brain.

                          And of course, 3 days after I drive 4 hours to get the panels I was setting for, (4 x 215w) 327w Sunpowers that are the same width show up on CL. UGH.

                          Comment


                          • #14
                            Originally posted by Withalligators View Post
                            How do I wire it all up properly?

                            I think I'll wire it in 2 pairs in series, running in parallel. Is that correct?
                            How many panels? 4 panels? If correct 2S2P

                            Originally posted by Withalligators View Post
                            Do I need a breaker on each positive lead? Even between panels? Or each series? Or just one coming into the controller, between the controller and batteries, and between the alternator and batteries? The data sheet for the panel has a 15A series fuse rating so I'll have one inline for each series.

                            What size should the breakers be?
                            No breakers required with 2 strings. You will need fuses or breakers between the controller and batteries, between alternator and batteries, and between the batteries and load. Something like this. Only thing that will be different is fuse and wire sizes.






                            MSEE, PE

                            Comment


                            • #15
                              Originally posted by Sunking View Post
                              ...... No breakers required with 2 strings. ......
                              Except, having breakers or a switch is very handy to compare string 1 vs string 2, and for the times you have to turn the controller off, you need to remove PV power , and restore it, in the proper sequence to battery power.

                              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

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