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  • Positive and Negative ground question

    Hi

    For the past year, after careful planning, we have been living off grid in our travel trailer. We have been using (2) 30VDC 250W grid tie solar panels, creating a total of 60VDC 500W. Sending this into a Tracer-2210RN MPPT controller which feeds (4) Duracell 6-volt golf cart batteries (12v system). The system seems to have been working okay for the past year. The indicator lights on the controller do what they are supposed to and blink when the batteries are supposedly fully charged.

    But now I have a question. As it turns out, the controller supposedly only handles 260W of solar panel input for a 12V system. Seems to me that something would have gone wrong by now since I am throwing 500W into the controller. Also, I read where its a positive ground controller. My aluminum panels have been sitting on the ground for the past year. And the controller is actually underneath the trailer pushed against the inside of the metal frame. It has a plastic container over it with a bungee strap holding it all in place. This was meant to be temporary but ended up working well enough to leave it be. Even though this system appears to have been working, should I be concerned with two things?

    1. Is the controller not making full use of the panel wattage, and is there any danger involved by potential overload. Even after a year?

    2. Should I be worried about using a positive ground controller?

    Lastly. The manuals talked about the "load" terminals on the controller. But I was under the impression at the time that it was just for automatic control of a security light. But am wondering if I am supposed to have something connected to the load to prevent overcharging? I could be wrong. The manuals aren't very good.
    Last edited by joem789; 07-19-2016, 10:36 PM.

  • #2
    What makes you think it is a positive ground controller? This manual says that part number is negative ground. I think you would have had trouble before now if the grounding was wrong.

    http://www.epsolarpv.com/en/uploads/...9586333456.pdf

    As an mppt controller, it may be able to protect itself from producing overcurrent. However, I think you are right, you are not fully utilizing the available panel power. Putting your batteries in series to make 24 V may be the best solution, all things considered.

    The load terminals are there to operate a relay or small load. You don't have to use them.
    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

    Comment


    • #3
      Excellent. I'm glad to see that I was wrong about the ground. I am not sure how I would be able to use my batteries as a 24V system since my travel trailer runs on 12V. Would I somehow step back down from 24V to 12V at the camper connection? Or would it make more sense to just buy another MPPT controller like I have and connect the 2nd panel to it and wire the controller to the batteries in parallel with the first controller?

      Comment


      • Logan5
        Logan5 commented
        Editing a comment
        to run 12 volt items, you use a 24 volt to 12 volt step down controller, 20 to 50 dollars online. does not make any sense to up grade controller only to maintain an inefficient 12 volt system. 24 volts is more efficient and easier to maintain.

    • #4
      Originally posted by joem789 View Post
      But now I have a question. As it turns out, the controller supposedly only handles 260W of solar panel input for a 12V system. Seems to me that something would have gone wrong by now since I am throwing 500W into the controller.
      No you are not pumping in 500 watts. It is being limited by the controller. A 20 amp into a 13 volt battery (12 Nominal) = 260 watts. To be able pass 500 watts would require a 40 Amp Controller, again 40 amps x 12 volts = 480 watts.

      Now at 24 volts you can run all 500 watts. All you have to do is reconfigure your batteries to 24 volts and get a 24 volt Inverter. So you have three options.

      Throw a 250 watt panel in the trash as you are not using it anyway.
      Replace Controller with a 40 amp MPPT if you wish to remain at 12 volt battery.
      Convert to 24 volt battery


      Originally posted by joem789 View Post
      Also, I read where its a positive ground controller.
      No it is not a Positive Ground controller. If anything is Negative Ground. If the Positive Polarity was grounded, the Controller would burst into flames if you followed the Instructions. Look at the Owners Manual, page 6, Fig 3.2.

      See the ground on the Negative Term Post of the Battery? If the Positive were Grounded to the Controller, and the controller bonded to ground. The Controller and battery wiring would burst into flames. So whatever you read or were told you was full of Crap.

      [QUOTE=joem789;n323571] 1. Is the controller not making full use of the panel wattage, and is there any danger involved by potential overload. Even after a year?

      Possible, but if a problem were to develop you would notice indicator lights going Stupid as a result of a malfunction.

      Originally posted by joem789 View Post
      2. Should I be worried about using a positive ground controller?
      Rubbish.

      Originally posted by joem789 View Post
      Lastly. The manuals talked about the "load" terminals on the controller. But I was under the impression at the time that it was just for automatic control of a security light. But am wondering if I am supposed to have something connected to the load to prevent overcharging? I could be wrong. The manuals aren't very good.
      Load port is just for small loads. Do not use it.
      MSEE, PE

      Comment


      • #5
        Ok thanks for the advice. I will just upgrade to the 40A controller.

        Comment


        • #6
          Originally posted by joem789 View Post
          Ok thanks for the advice. I will just upgrade to the 40A controller.
          Honestly, I think you are better off rewiring the battery to 24 V and buying a stepdown to 12 V if you need it. You take an efficiency hit with the extra component in there (assuming you actually have 12 V loads and can't just swap to a 24 V inverter), but make up for it somewhat with better cc efficiency. At 24 V, you won't have to upgrade your wiring to handle the extra current, and having the batteries in series may help prolong their life and avoid that replacement cost.
          CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

          Comment


          • #7
            Sensij

            I like your idea. It occurred to me beforehand. But I wasn't sure how practical it is. Do you have any idea what the specs would need to be for a step down for my system? I typically see them listed in watts. Like an inverter. But I am not sure if it needs to be rated according to my panel wattage (550W), number of batteries (4 (6v) golf), or what. Any ideas?

            Comment


            • ButchDeal
              ButchDeal commented
              Editing a comment
              it would need to be rated based on the load you plan to run at 12V

          • #8
            Okay I see. Honestly I don't really know what the load typically is in our camper. The things that use the 12V system are the lights, exhaust fan, the propane fridge electronics, and the cigarette lighter that we typical use with a 120W inverter for charging laptops and phones. So possibly, this would work? https://www.amazon.com/Pyle-PSWNV720.../dp/B003P17X8I

            Comment


            • Logan5
              Logan5 commented
              Editing a comment
              This will work and Pyle makes some good products

          • #9
            Our camper typically uses the 12V system to run our lights, exhaust fan, propane fridge electronics, and the cigarette lighter socket that uses our 120W inverter for charging laptops and phones. Would the Pyle PSWNV720 converter do the trick you think?

            Comment


            • #10
              That is the exact model 12 volt converter I use in an off-grid cabin. It works for me, but you will still have to add up your loads and see if it will work. It is rated for 360 watts continuous, so stay well below that. Also consider a good quality shut off switch for between the battery and the device. That way you can shut it all down. The Pyle converter itself draws from the batteries a tiny bit even when idle.

              Just so you have an idea, I have a ceiling fan, furnace fans,almost 20 led lights, and stereo, and can run them all at once. We are somewhat close to the continuous limit by my calcs if we have everything running at the same time.

              Hopefully last edit I should also mention that it works very well in keeping a constant voltage to everything. The voltage output stays the same regardless of where our 24 volt bank is at voltage wise. This was a happy accident, but I like the feature.

              If you don't know where to start, look on the fridge and find the amp rating at 12 volts. If for example it said 7.5 amps @ 12 then you know that part is 90 watts. Then add up your lights and multiply that number by a single light amp rating. Just get close, and figure high so you have some breathing room.
              Last edited by cabindave; 07-22-2016, 03:47 PM.

              Comment


              • #11
                Just be sure your propane fridge does not try to use the 12V for anything else besides the electronics. Usually, propane fridges use 12 to generate heat instead of using the propane. That is hugely inefficient with a PV system.
                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
                  Originally posted by Sunking View Post

                  ...
                  Throw a 250 watt panel in the trash as you are not using it anyway.
                  Wouldn't the second panel be helpful in conditions where a single panel would be producing less than 260W? Let's say you have cloud cover and each panel is only producing 130W. Wouldn't you then be using the full power of both panels? And wouldn't you regret having thrown one away??

                  Comment


                  • #13
                    Originally posted by tastewar View Post

                    Wouldn't the second panel be helpful in conditions where a single panel would be producing less than 260W? Let's say you have cloud cover and each panel is only producing 130W. Wouldn't you then be using the full power of both panels? And wouldn't you regret having thrown one away??
                    I believe the problem is your charge controller. The fact that your charge controller can't handle the current your panels generate, it's limiting the current and thus rendering one panel basically ineffective.


                    I'm new to this, but your setup is very similar to what I've been pondering building. I'm pretty certain if you changed your battery configuration to 24v you'd see significant gains in efficiency, as well as being able to take advantage of both of your panels with your charge controller (assuming it's rated to handle both when run at 24v)

                    Comment


                    • #14
                      Originally posted by Sunking View Post

                      No you are not pumping in 500 watts. It is being limited by the controller. A 20 amp into a 13 volt battery (12 Nominal) = 260 watts. To be able pass 500 watts would require a 40 Amp Controller, again 40 amps x 12 volts = 480 watts.

                      Now at 24 volts you can run all 500 watts. All you have to do is reconfigure your batteries to 24 volts and get a 24 volt Inverter. So you have three options.

                      Throw a 250 watt panel in the trash as you are not using it anyway.
                      Replace Controller with a 40 amp MPPT if you wish to remain at 12 volt battery.
                      Convert to 24 volt battery



                      Pick one of the last two options this person offered and you'll collect twice as much current (electricity, energy) from the sun for your batteries.

                      Replacing your controller with a 40a rated one is likely the easiest in terms of labor.

                      BUT, if you change your system to 24v, you not only use all of your solar panels, you also gain a bunch of efficiency.

                      Comment

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