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  • Combining grid, solar and back up generator

    Hi group - first time posting.

    I currently live out in the backblocks of Myanmar where we rely on a mix of solar and a couple of hours of (community owned) diesel generated electricity per day. Unfortunately, after a year of, in hindsight, mismanaging my batteries, they are now pretty well screwed.

    Our system is set up so that the inverter will give priority to incoming generated power over solar, and will also help to recharge batteries when the generator is running. When the generator switches off, the batteries automatically kick in again as the power source.

    For those that want to know more detail, the solar system comprises of:
    4 x 300w panels
    1 x 60A MPPT controller
    4 x 200 ah 12v batteries in series/parallel to provide 400 ah 24v
    1 x 3000w inverter


    However - things are about to change!!!!

    The poles have gone in the ground to bring in national grid electricity - we are just waiting for the wires and then for someone to flick the switch. However, the above mentioned batteries may not last that long, so I have purchased my own small 3kw petrol generator as a private back up and now want to wire it into the system. A generator costs the same as one battery and is better able to be used in other situations if required, so I saw that as being a better option than buying four new batteries in the short term

    My intention is that:
    1/ the diesel generated (to be replaced by national grid soon) supply still takes precedence and supply source.
    2/ should the diesel generation stop, or the national grid go down (almost guaranteed on a daily or every second day basis), the battery bank will take over as it does now. The bank, while not in good condition, should be being kept fairly well topped up between the sun when it shines and the new feed from the grid.
    3/ if all else fails, we will crank up the petrol generator, endure the noise and pay the running costs.

    I want to wire the generator into the main supply board (not me, but a qualified electrician) as a surrogate for the national grid and so actually be mirroring what happens now with the community generator. That basically means a simple changeover switch taking one feed or the other. But I also want to do it in a way that once the national grid kicks in, the small generator will automatically cut out so we limit the noise and drain on the wallet.

    Can someone come up with a wiring diagram that will show this set up? I tried explaining the concept of solenoids, cut out switches etc to my local wiring man but language is a problem and while we have access to most basic parts here, there are some things that we take for granted in the west that are simply not available or are unheard of here.

    Thanks so much in advance


  • #2
    Maybe you can give us a rough sketch ?
    How many homes does the 3Kw inverter supply - What's it model # ? does it have AC1 & AC2 (grid & Generator) inputs ? What is your AC Voltage ? 120V or 240V ?
    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


    • #3
      Hi - the inverter only supplies our house - fairly basic in terms of appliances etc. We are supposedly 240v.


      Attached are some photos of what we have and a link to the Sandi site for more specs on the inverter http://www.sandi-solar.com/ProductShow.asp?ID=19

      IMG_20190919_113506.jpgIMG_20190919_113553.jpgIMG_20190919_113514.jpgmain board.jpg

      Note that the position of the crossover switch between grid/generator and battery feed is largely immaterial. The inverter will automatically detect if it needs to be in 'inverter' mode or 'UPS charger' mode. The small green round button switch will take the inverter feed out of play if required (photo 4)

      Photo 2 shows the red and black cables coming directly from the batteries, and the blue cables are feeds into and out of the inverter back to the main board detecting if an external supply is coming in, so determining what mode the inverter needs to be in.

      One simple possible solution is to wire things up as below
      possible solution.jpg

      However, this is not a perfect solution and doesn't solve all my problems.

      1/ In a perfect world, should the main supply be down and then battery charge levels get too low, the auxiliary would be wired up to automatically come on. This one is probably wishful thinking.
      2/ The more likely scenario is that the inverter would start chirping at me its warning that the battery charge was low, and I would manually change the crossover switch to the auxiliary input and then start the generator up.
      3/ When the main comes back on, we need the auxiliary to shut down. That could be done by wiring in a kill switch on the generator after, say, a 5 second delay. The lead could be taken from the red indicator light which comes on when the main's supply is operative.
      4/ However, that doesn't throw my new crossover switch back to the main grid feed in. If my main grid is not feeding in, the batteries automatically kick in, but they are probably low already because if they weren't, the auxiliary wouldn't have needed to be used in the first place.

      It's fine if I actually happen to be in the house and can make the switch manually. However, there's every chance I won't be. Are there switches that automatically default to one position if the feed in required is present?

      All constructive comments welcomed!!

      Comment


      • #4
        Automatic transfer switches are pretty expensive, but you may be able to make a DIY out of relays
        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
          Originally posted by Mike90250 View Post
          Automatic transfer switches are pretty expensive, but you may be able to make a DIY out of relays
          I set out to build my own using interlocked contractors. I started sourcing parts and found that I could buy one ready made for less.

          I shopped Platt Electric locally and eBay. Perhaps you could point me to a better source?

          Thank you.

          Comment


          • #6
            Generac, Granger Supply, or any of the whole house generator companies. $700+ are the numbers I've seen.

            Maybe get a large computer UPS for the fridge (cheap on ebay with toasted batteries, replace with golf cart batteries) (large commercial UPS for server room, not home owner)

            and do manual transfer switches for rest ? Commercial ones, may have generator start contacts too.
            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


            • #7
              Originally posted by Mike90250 View Post
              Generac, Granger Supply, or any of the whole house generator companies. $700+ are the numbers I've seen.

              Maybe get a large computer UPS for the fridge (cheap on ebay with toasted batteries, replace with golf cart batteries) (large commercial UPS for server room, not home owner)

              and do manual transfer switches for rest ? Commercial ones, may have generator start contacts too.
              I don't think we are talking about the same thing. The ones that I have used on other projects have run $80-$200. The one I am using on this one is a bit over $80. The parts for me to duplicate it were well over $100 plus the time to assemble it.

              https://www.amazon.com/Go-Power-TS-3...34989828&psc=1

              https://www.amazon.com/Go-Power-Auto...86334423&psc=1
              Last edited by PNW_Steve; 09-22-2019, 03:59 PM.

              Comment


              • #8
                I confess, I've not seen tiny ATS before, I assumed you needed whole house
                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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