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  • DIY Auto transfer switch questions?

    Hey Everyone,

    I am working out the electrical systems for my RV conversion and have run into questions regarding my inverters and ATS.

    Trying to be a bit creative and frugal I thought that I would look into building my own.

    Just to be clear, I want certain receptacles to be fed shore power and when shore power disappears I want them to switch over to inverter power.

    As I pondered the problem and potential solutions I came upon the idea of simply using a DPDT relay with the coil connected to the shore power connection.

    No shore power=Coil de-energized=Inverter connected to load
    Shore power on=Coil energized=Shore power connected to load

    This can't work. It's too simple...... What am I missing? I don't need a time delay like my generator transfer switch.

    Any thoughts?

  • #2
    By the time you work out the fail-safes, you may as well buy a certified ATS (Automatic Transfer Switch)

    Is this for 120V or 240V ?
    one that looks to not be junk https://www.solar-electric.com/pomax...AaAuk6EALw_wcB
    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
      120V.

      For a simple 120V transfer switch with no need for time delay what fail-safes are you referring to?

      Comment


      • #4
        It's hard to beat the one i linked to, if it covers your amps.
        Fail-safe. simple relays, switching household loads, can sometimes weld contacts and that will mess up your day. If you do a DIY and something burns up, insurance will not cover you.

        if you install a UL rated switch, it's not likely to burn up, and if it did, your insurance should cover the losses
        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
          . If you do a DIY and something burns up, insurance will not cover you.
          This whole project is DIY. I am converting a school bus to an RV.

          Comment


          • #6
            Originally posted by Mike90250 View Post
            By the time you work out the fail-safes, you may as well buy a certified ATS (Automatic Transfer Switch)

            Is this for 120V or 240V ?
            one that looks to not be junk https://www.solar-electric.com/pomax...AaAuk6EALw_wcB
            Looks good for it's intended application but, as far as I can tell, it will not play in my application as the time delay is fixed.

            Comment


            • #7
              Oops. Posted on the wrong thread.

              But, please feel free to comment on my question.
              Last edited by PNW_Steve; 02-18-2018, 01:06 PM. Reason: Wrong thread

              Comment


              • #8
                Maybe you need a large computer style UPS ?
                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


                • #9
                  Originally posted by Mike90250 View Post
                  Maybe you need a large computer style UPS ?
                  Not sure how a UPS fits in to the discussion?

                  Comment


                  • #10
                    They have ATS in them. And an inverter. And quick switch-over time, no glitching the computer. Even if you have your DIY transfer switch, how do you turn the inverter on, or are you leaving it on all the time ? If you leave it on all the time, just get a semi-smart battery charger to keep the batteries charged, and run off the inverter 24/7

                    I'm trying ideas to help you out. maybe jar a random stray thought loose
                    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


                    • #11
                      Build your own, perhaps? I've built a couple, like this Auotmatic Transfer Switch on Robert's site. They work great, and have for some time. If the relay fails, just unplug and replace it with another one.
                      Paul

                      Comment


                      • #12
                        Originally posted by livingincebu View Post
                        Build your own, perhaps? I've built a couple, like this Auotmatic Transfer Switch on Robert's site. They work great, and have for some time. If the relay fails, just unplug and replace it with another one.
                        Thank you for sharing that link. That is exactly what I was considering. It looked like it should work but I was concerned that I may be overlooking something that could bite me in the backside.

                        Comment


                        • #13
                          Originally posted by PNW_Steve View Post
                          Thank you for sharing that link. That is exactly what I was considering. It looked like it should work but I was concerned that I may be overlooking something that could bite me in the backside.
                          Like I said, no worries. Just mount the relay base for your circuit and you can plug / unplug the relay whenever needing to replace it. easy peasy. Just leave all power cords plugged in, otherwise. Not sure if he is a member here. But, the guy who made the project I copied, goes by 2manytoyz, on at least one other solar related forum of which I am a member. Give 'er a try. Worst case, you are out a few bucks. Best case, you will be making more of them.

                          In fact, Robert (2manytoyz) may be the person who uses a similar circuit to switch between two appliances, a refrigerator and a freezer, in order to be able to run both from a single, smaller inverter. I believe, when the freezer is powered, the relay breaks the connection for the power feeding the refrigerator. When its compressor drops out, the refrigerator can then be powered. Pretty nifty idea, whomever came up with it. I will be using one of these for the same purpose, at our farm. We now have two refrigerator / freezer units out there and only want one running at a time. It's easier (READ: cheaper) to do that, than to worry about trying to get another PSW inverter from the states.
                          Paul

                          Comment


                          • #14
                            Originally posted by Mike90250 View Post
                            They have ATS in them. And an inverter. And quick switch-over time, no glitching the computer. Even if you have your DIY transfer switch, how do you turn the inverter on, or are you leaving it on all the time ? If you leave it on all the time, just get a semi-smart battery charger to keep the batteries charged, and run off the inverter 24/7

                            I'm trying ideas to help you out. maybe jar a random stray thought loose
                            Thank for the suggestions.

                            This is for an RV with 4x L16 batteries and a Prosign 1800/24 inverter. I have everything lined out except the shore/inverter transfer switch.

                            Comment


                            • #15
                              Originally posted by livingincebu View Post

                              Like I said, no worries. Just mount the relay base for your circuit and you can plug / unplug the relay whenever needing to replace it. easy peasy. Just leave all power cords plugged in, otherwise. Not sure if he is a member here. But, the guy who made the project I copied, goes by 2manytoyz, on at least one other solar related forum of which I am a member. Give 'er a try. Worst case, you are out a few bucks. Best case, you will be making more of them.

                              In fact, Robert (2manytoyz) may be the person who uses a similar circuit to switch between two appliances, a refrigerator and a freezer, in order to be able to run both from a single, smaller inverter. I believe, when the freezer is powered, the relay breaks the connection for the power feeding the refrigerator. When its compressor drops out, the refrigerator can then be powered. Pretty nifty idea, whomever came up with it. I will be using one of these for the same purpose, at our farm. We now have two refrigerator / freezer units out there and only want one running at a time. It's easier (READ: cheaper) to do that, than to worry about trying to get another PSW inverter from the states.
                              I saw a similar setup for running two roof a/c's on an RV years ago.

                              It sounds like you have had to replace relays periodically. Is that correct? What sort of failure are you seeing?

                              Comment

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