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Help PLEASE sizing up my new solar system for my camper

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  • Help PLEASE sizing up my new solar system for my camper

    hello all

    So the last time i installed solar for my camper i screwed up!
    So this time i thought i would get some proper advice first
    I am considering 300 watts of solar and 4 x 6 volt t105 trojan batteries + installing an isolator to the car battery.

    I would like to run

    2 x 12 volt fantastic fans (8 hours a day) (1-3 AMPS)
    1 x Whynter 45 quart fridge (24hours) (65 WATTS /0.75AMPS)
    8 x LED lights (running 5 hours a day)(60 WATTS / 8AMPS)
    1 x nutribullet (10 min a day) (600 WATTS / 6.7AMPS)
    1 x 12 volt shurflo pump (15 min a day) (7AMPS)
    1 x coffee machine for the morning only (600 WATTS / 6.7AMPS)
    need to charge laptops and cell phones as well


    i think i have figured out the amps right but if i haven't please advise otherwise

    i will also try and get everything in DC power instead of using our 1100 watt inverter which i will only use to charge laptops etc.

    PLEASE HELP AND ADVISE it would be much appreciated so i don't screw this up again and ruin my batteries

    Thanks in advance!
    Sami

  • #2
    Hello sami_h23.

    What you have provided is not really enough and possibly misleading to determine your daily watt hour usage which is needed to size the battery and panel wattage.

    Knowing the amp rating is not that reliable since you don't really know the voltage it will use. You need a true voltage and amp to calculate the watts a load draws ( V x A = W).

    A better way to determine your daily usage would be to use the watt rating times the number of hours the load runs each day.

    A much better way is to use a "kill a watt" meter and let it measure the daily watt hour usage.

    But for simplicity you can use the load's watt rating and multiply it by the number of hours. That provides an estimate of the watt-hours used.

    Once you know that value for each load you can total them up to get an overall estimate of the daily watt hours. From there you can size your battery system and panel wattage.

    Go back and try to find the watt rating of each load. Then we can see if that 12volt 210Ah battery system is big enough along with if 300 watts and the charge controller is enough to recharge the battery each day.

    Comment


    • #3
      Hi Sun Eagle

      So i think i have figured it out

      2 x 12 volt fantastic fans (8 hours a day) 36 watts x 8 hours = 288
      1 x Whynter 45 quart fridge (24hours) 65 watts x 24 hrs = 1536 ( i don't think this fridge will consume that much energy as i read that the most it will use is 25 amps per day)
      8 x LED lights (running 5 hours a day) 48 watts x 5 = 240
      1 x nutribullet (10 min a day) 600 watts x .80 = 52.8
      1 x 12 volt shurflo pump (15 min a day) 92.4 watts = 23.1
      1 x coffee machine for the morning only 800 watts = 40
      need to charge laptops and cell phones as well ( this i'm not so concerned about)

      Please let me know if this seems right!
      Last edited by sami_h23; 12-11-2017, 02:34 PM.

      Comment


      • #4
        Also what solar power control charger would you recommend?

        Comment


        • #5
          Originally posted by sami_h23 View Post
          Hi Sun Eagle

          So i think i have figured it out

          2 x 12 volt fantastic fans (8 hours a day) 36 watts x 8 hours = 288
          1 x Whynter 45 quart fridge (24hours) 65 watts x 24 hrs = 1536 ( i don't think this fridge will consume that much energy as i read that the most it will use is 25 amps per day)
          8 x LED lights (running 5 hours a day) 48 watts x 5 = 240
          1 x nutribullet (10 min a day) 600 watts x .80 = 52.8 (600 x 0.8 = 480wh)
          1 x 12 volt shurflo pump (15 min a day) 92.4 watts = 23.1
          1 x coffee machine for the morning only 800 watts = 40 ??
          need to charge laptops and cell phones as well ( this i'm not so concerned about)

          Please let me know if this seems right!
          Ok if you add up the calculated watt hours you get:

          288 + 1536 + 240 + 480 + 23.1 = 2567.1 wh + the coffee machine which is quite a lot for a 12volt system.

          You are probably correct that you will use less than 1534wh for that fridge but hard to say how efficient it is.

          Anyway, once you come up with the total watt hours you then divide that by the battery voltage and multiply that by 4 (which is based on only using 25% of the total Ah of the battery system).

          So for yucks and giggles lets use 2600 wh / 12 volt x 4 = a battery system rated 867 Ah. That is a huge battery system and will require over 1000 watts of panels and an 80amp MPPT CC.

          So you have to decide if you really need to determine what your true daily watt hour usage is or run those big loads from something other than the batteries.

          Comment


          • #6
            Originally posted by sami_h23 View Post

            I would like to run

            2 x 12 volt fantastic fans (8 hours a day) (1-3 AMPS) 2 amps x 12 volts x 2 units x 8 hours = 384 Watt Hours
            1 x Whynter 45 quart fridge (24hours) (65 WATTS /0.75AMPS) 65 watts x 12 hours (50% duty cycle) 780 watt hours
            8 x LED lights (running 5 hours a day)(60 WATTS / 8AMPS) 60 watts x 5 hours = 300 watt hours
            1 x nutribullet (10 min a day) (600 WATTS / 6.7AMPS) 600 watts x .16667 hours = 100 watt hours
            1 x 12 volt shurflo pump (15 min a day) (7AMPS) 84 watts x .25 hours = 21 watt hours
            1 x coffee machine for the morning only (600 WATTS / 6.7AMPS) 600 watts x 1 hour = 600 watt hours
            need to charge laptops and cell phones as well Insignificant.


            i think i have figured out the amps right but if i haven't please advise otherwise
            No Sam you have not figured Amps out and no reason to bother with amps. Everything is done with watt hours. Example this:

            1 x coffee machine for the morning only (600 WATTS / 6.7AMPS)
            Complete nonsense. 600 watts @ 120 volts is 600/120 VAC = 5 amps. However I assume this uses an Inverter from a 12 volt battery. Assuming the Inverter is 80% efficient the coffee power pulls 600 watts / .8 eff = 750 watts. 750 watts / 12 volt battery = 62.5 amps. I have no clue where you came up with 6.7 amps. Not that it matters because you can care less what the Amps are. It is Watt Hours you need to know. Now get ready for the bad news.

            Using your numbers I estimate you need 2185 Watt Hours aka 2.185 Kwh per day. That is a huge number, I am just going to round up to 2200 watt hours per day.

            Sense this is an RV with part time use you can get away with 3-day reserve capacity on the battery or 6.6 Kwh of capacity. For a 12 volt system you would need a 6600 wh / 12 volts = 550 AH @ 12 volts. battery. 4 x T-105 batteries is not quite enough as that only yields 12 volts @ 450 AH. You could make the T-105's work but will require that you run the engine alternator every day for a few hours.

            As for panel wattage, it can be whatever you watt because there it is almost impossible for you to have enough panel wattage to generate 2.2 Kwh per day of usable power. Example the minimum required with a 12 volt 450 AH battery to generate at least C/10 charge current 45 amps is 600 watts. Even at 600 watts is not likely to generate 2.2 Kwh usable power a day on an RV. So it does not really matter what wattage you use as it will not generate enough power.

            You are going to need the battery Isolator and/or a generator running a couple of hours everyday while in use. The panels will keep the batteries charge up while not in use. You can make it work, just not the way you had visioned.
            MSEE, PE

            Comment


            • #7
              Ok so let's forget about the coffee machine.

              only have the fans, lights, 600 watt vitamix and an ARB fridge. Using the 50l fridge

              would 300 watts of solar and 4 x 6 volt deep cycle batteries be enough?

              thanks for you're help guys I'm hopeless at this

              cheers
              sami

              Attached Files

              Comment


              • #8
                Originally posted by sami_h23 View Post
                Ok so let's forget about the coffee machine.

                only have the fans, lights, 600 watt vitamix and an ARB fridge. Using the 50l fridge

                would 300 watts of solar and 4 x 6 volt deep cycle batteries be enough?

                thanks for you're help guys I'm hopeless at this

                cheers
                sami
                With 300 watts of panels and an MPPT CC you can get at most 25 charging amps. That will work with a 12v 250Ah battery system. The most you can draw from it daily is about 750 watt hours.

                Now if you have a PWM type CC that 300 watts may get you about 15 charging amps. That will work with a 12v 150Ah battery system. The most you can draw from it daily is about 450 watt hours.

                So depending on which CC and battery system you get you may or may not be able to run your loads which include the refrigerator.

                Comment


                • #9
                  Sam with 300 watts of panels limits what size battery you can run. Unless you plan on driving every day for a couple of hours your battery size is limited. Do not even think about purchasing a PWM controller as that turns your 300 watt panels into 200 watts. Buy a quality 30 amp minimum MPPT Controller. OK with a 300 watt panel and 30 amp controller the panels can support a 12 volt 200 to 250 AH battery. That would be a pair of 6-volt Golf Cart Batteries like a pair of Trojan T-105's. They will not support 4 x 6-volt batteries as you mentioned.

                  Based on 3-day reserve capacity gives you roughly 1 Kwh of usable energy per day. If you drive at least 2 hours 2 Kwh per day.
                  MSEE, PE

                  Comment


                  • #10
                    Hi thanks so much for coming back to me I have purchased the 30amp mppt charge controller and I have 300 watts of solar.
                    may I ask why you would recommend 1 x 12 volt battery over 2 x 6 volt batteries?
                    also last question isn't it if I have more batteries it can store more power so wouldn't it be better to get more batteries?

                    Comment


                    • #11
                      Originally posted by sami_h23 View Post
                      Hi thanks so much for coming back to me I have purchased the 30amp mppt charge controller and I have 300 watts of solar.
                      may I ask why you would recommend 1 x 12 volt battery over 2 x 6 volt batteries?
                      also last question isn't it if I have more batteries it can store more power so wouldn't it be better to get more batteries?
                      What Sunking is saying that a better way to build a battery system is to have all of them wired in series instead of in parallel.

                      So you can use 2 x 6V 232Ah batteries wired in series to make a 12v 232Ah system or 4 x 6V 115Ah batteries wiring two sets of 2 in parallel to make a 12v 230Ah system. Both have roughly the same output.

                      The first system is better than the second because you run the risk of different resistance along each "parallel" paths. That will cause unequal charging and discharging which will usually kill off one or more batteries earlier then expected.

                      Comment


                      • #12
                        Originally posted by sami_h23 View Post
                        also last question isn't it if I have more batteries it can store more power so wouldn't it be better to get more batteries?
                        The problem is that the size of the solar array is limited, so over-sizing the batteries would cause them to die an early death from chronic under-charging.

                        Steve Dold
                        Say NO to useless over-quoting

                        Comment


                        • #13
                          Originally posted by sami_h23 View Post
                          Ok so let's forget about the coffee machine.

                          only have the fans, lights, 600 watt vitamix and an ARB fridge. Using the 50l fridge

                          would 300 watts of solar and 4 x 6 volt deep cycle batteries be enough?

                          thanks for you're help guys I'm hopeless at this

                          cheers
                          sami
                          I own both an ARB 50L (older model) and a Dometic 80L. Here's some #'s that might help you calculate daily usage.

                          If you use the ARB as a fridge the duty cycle is roughly 20-25%. If you use it as a freezer the duty cycle approaches 40-45% I keep mine in the back of my 4Runner year round. It averages about 250-400wh daily. Mine is set to 40* F.

                          The Dometic lives in my trailer. It uses roughly the same amount of power as the ARB. 300-400wh daily. Set to 40*F.

                          YMMV of course, but pretty much all the 12/24v compressor fridges use either a danfoss or sawafuji compressor so the #'s should be pretty comparable between fridge sizes.

                          Comment


                          • #14
                            Originally posted by sami_h23 View Post
                            may I ask why you would recommend 1 x 12 volt battery over 2 x 6 volt batteries?
                            Never ever parallel Pb batteries. I never said use a 12 volt over 6 volt. If you need 12 volts at 200 AH, then buy 200 AH batteries. Not two 12 volt 100 AH batteries wired in parallel. If you could find a 12 volt 200 AH battery would weight 140 pounds. 6 volt 200 AH batteries weigh 75 pounds. If you use parallel batteries, you cut life 50%. In other words instead of 2 years of service you get 1 year.

                            Originally posted by sami_h23 View Post
                            also last question isn't it if I have more batteries it can store more power so wouldn't it be better to get more batteries?
                            Nope. Would you get fatter if you only ate 1 slice a bread each day, or would you die in a month or two from starvation?

                            Batteries have minimum charge requirements and perfection is C/10 to C/8/ So on say a 100 AH battery is 10 to 12 amps. Charge it with 5 amps and it starves to death. You would never get the battery charged if it is used.

                            You have a disease called Stuck In A 12 Volt Box Very easy to cure if you can swallow the medicine served here..
                            Last edited by Mike90250; 12-15-2017, 08:37 PM. Reason: Mod edit & trim final line
                            MSEE, PE

                            Comment


                            • #15
                              Sami, when you are designing a solar power system, you need to identify which equipment will be powered by 110V AC and 12V DC. Don't forget the motor starting current is usually 3-7x of the rated current for few seconds. For example, a 12V 24W fan may need up to 14A during the motor startup without soft starter (power electronics). Using inverter to drive AC motor, pump or compressor is not recommended because the oversized inverter will be required to support the motor startup.

                              For the fridge, the diversity of the usage shall be estimated correctly. I will say a good fridge with low usage (the fridge is accessed for less than 10 times a day) will only turn on approximately 5 hours a day at 25 degree Celsius.

                              Next, you need to size the battery. If you have so many devices that will source from an inverter, connect the batteries in series, which gives higher DC voltage, will offer less conversion loss (No higher than 48V is recommended- refer to the probability of heartfibrillation curve in IEC standard). However, if there are high demand for the 12V DC devices, I will suggest the batteries to be connected in parallel, and those batteries shall be of same manufacturer and batch. Moreover, those parallelled batteries are required to be monitored regularly to prevent any fault current circulates within the parallel battery bank. Capacity (AH) and the C value are important. Usually, a lead acid battery can sustain high current output for a short period. Continuous high current output will significantly shorten the battery's service lifetime. That's why you need to decide whether your system is high voltage - low current (series: inverter + Buck converter) or low voltage - high current (parallel: direct DC supply + inverter).

                              Finally, use the battery bank design to determine the size of the solar panel and the type of charge controller required. Don't forget during the day time, the solar panel can also supply the loads and that shall be included in your calculation.

                              Former power system grounding system engineer - now sparky business owner.

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