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  • DPDT Switch?

    If I have a positive and negative line from my panel array that I want to switch from going a (charge controller > batteries (when full)) to a grid tie inverter, can I use some sort of DPDT switch? I can't find any products that.

    I want to use the panels to charge the batteries first, but when they are full, I want to use them to supplement the house power.

  • #2

    Re: DPDT Switch?

    Re: DPDT Switch?

    To answer your question we need to know details of your array, combiner, and the inverters. You may need to have the array in a different configuration for each of the inverters. From your question it is not clear to me if you want to sell to the grid or not. Either way, there are inverters on the market that will do what you want, without the need for an external DPDT switch.

    --vtMaps
    4 x 235w Samsung, Outback fm60 & vfx3524 & mate, Midnite E-panel, four Interstate L16, Trimetric monitor, Honda eu2000

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    • #3

      Re: DPDT Switch?

      Re: DPDT Switch?

      One of the big issues in my mind is the very real possibility of DC arcing inside that DPDT switch. Depending on the switch design and the DC voltages involved, an arc could easily be initiated between the internal + and - components, destroying the switch and possibly causing a tragic fire.
      1900 watts PV, (1000 watts PV feeding MidNite Classic 150; 900 watts PV + 160 watts micro hydro both feeding into a single shared Morningstar TS-MPPT-60) ; Xantrex Pure Sine 1800/12 for heavy loads; Xantrex Pure Sine 1000/12 on 24/7 for everything else; six Rolls Surrette 2 volt L16 @ 12 volts.
      Domestic hot water totally provided by the sun 8 months out of every year via thermal panel.

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      • #4

        Re: DPDT Switch?

        Re: DPDT Switch?

        What I want to do is start with 4 128W/24V/5.33Amp panels in serial. I want to possibly double that in the near future. Because I plan on having up to 8 of the same panels, I am going have the main wires between the panels and the DC kill switch be 4 AWG. Overkill on wire for now, but planning for the future.

        I am going to use a morningstar 45 Amp MPPT charge controller for the batteries. When the batteries are full, I want to use the panel output and feed into the home. Not looking to sell back, just supplement what the home used during the day. Almost every inverter I see uses 12, 24 and/or 48 V input so I configured the panels so I could direct the same voltage to either the charge controller or the inverter.

        The piece I don't get is how to switch the panel output to either the charge controller for the batteires or the inverter when the batteries are full.

        Comment


        • #5

          Re: DPDT Switch?

          Re: DPDT Switch?

          You may not need to switch at all. Once the batteries are full, they will not be pulling any more power from the array so you might be able to just feed them in parallel.

          However, it depends on whether or not your grid tie system will leave enough to keep the batteries charged.

          Also not sure why you ran such heavy wire for a rather high voltage DC.
          Northern Arizona Wind & Sun Forum & Website Administrator

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          • #6

            Re: DPDT Switch?

            Re: DPDT Switch?

            Originally posted by goingtoghana View Post
            If I have a positive and negative line from my panel array that I want to switch from going a (charge controller > batteries (when full)) to a grid tie inverter, can I use some sort of DPDT switch? I can't find any products that.

            I want to use the panels to charge the batteries first, but when they are full, I want to use them to supplement the house power.
            This is the second time this question has come up in as many days.
            Don't even bother to try is my advice.
            Grid tie inverters are not designed to be fed the output of a charge controller. They have their own MPPT function on the input, whereas the output of a controller is meant to charge batteries. This will be 'electrically incompatible'.
            If you want to switch the array from the controller input to a GTI that is another matter, also with problems. For one thing the Voltage level will not be right; arrays design to charge batteries are typically much lower than those designed to power GTI's. One exception here would be micro-inverters which are meant to be connected to a single panel. Their you get the reverse problem; the array in total will be too high a Voltage. Another exception would be to use the Xantrex 600 Volt 80 Amp MPPT controller with a high Voltage array.
            This is a no-go idea. Not impossible to get it to work, but costly and more trouble than it's worth.

            What we normally do in the off-grid world is use a controller with an AUX function (Outback, MidNite) that can be programmed to operate an "opportunity load" when the battery charge reaches a certain state (Absorb, Float). This is the safest and most sure-fire method of capturing those Watt hours that would otherwise be lost.
            1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

            Ohm's Law: Amps = Volts / Ohms
            Power Formula: Watts = Volts * Amps

            Comment


            • #7

              Re: DPDT Switch?

              Re: DPDT Switch?

              Not understanding why you say I don't need a switch. Are you saying grid tie the batteries to the house circuit? (Panels > MPPT charge controller > Batteries > Grid Tie Inverter)? If I did that, would the batteries not be "used" if the main current to the house stays on from the street? In other words, at night when not generating current from the panels, would the house system try to pull current from the street and the batteries thus draining the batteries?

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              • #8

                Re: DPDT Switch?

                Re: DPDT Switch?

                Originally posted by Cariboocoot View Post
                This is the second time this question has come up in as many days.
                What we normally do in the off-grid world is use a controller with an AUX function (Outback, MidNite) that can be programmed to operate an "opportunity load" when the battery charge reaches a certain state (Absorb, Float). This is the safest and most sure-fire method of capturing those Watt hours that would otherwise be lost.
                So, the controller AUX function sends current to a grid tie inverter then?

                Comment


                • #9

                  Re: DPDT Switch?

                  Re: DPDT Switch?

                  Originally posted by Cariboocoot View Post
                  Grid tie inverters are not designed to be fed the output of a charge controller. They have their own MPPT function on the input, whereas the output of a controller is meant to charge batteries. This will be 'electrically incompatible'.
                  From what I gather, he does not really have a "grid tie" inverter - he has some inverters that will put out AC that he can somehow tie into the house for power. Apparently he is also not in the US.

                  However, details on exactly what he has are lacking.

                  Need to know exactly what you mean by "grid tie inverter", and what model/brand.
                  Northern Arizona Wind & Sun Forum & Website Administrator

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                  • #10

                    Re: DPDT Switch?

                    Re: DPDT Switch?

                    Originally posted by goingtoghana View Post
                    So, the controller AUX function sends current to a grid tie inverter then?
                    No. The AUX function merely controls a relay which can be used to switch on/off any number of things. There is no grid tie inverter involved.
                    The batteries power an off-grid inverter, correct? Under normal circumstances the loads on that will vary but remain fairly light. What you want to do is use the AUX function to turn on loads (AC or DC) that will make use of the power that is available from the panels but will not draw from the batteries.

                    Example (from my own system): batteries full, panels putting out less than 5 Amps @ 27.6 Volts. Panels are capable of 20+ Amps, meaning there are approximately 360 Watts available from the panels that aren't being 'harvested'. Over two hours this ads up to 720 Watt hours that are unrealized. Solution; turn on the water pump. It runs, fills the pressure tank, and I have water for a day without having 'tapped in to' any of the power stored in the batteries. In fact my whole system is balanced (somewhat precariously) this way; the batteries serve mainly as a power source for over night. During daylight hours the panels 'run everything' including charging up the batteries.

                    I'm not sure what you mean by Grid Tie inverter either. Here that would mean one that pushes AC to the household wiring and/or to the utility (if allowed and there is surplus). As per my previous post I know of none that would be truly compatible with a standard off-grid array. Not any that would be recommended for use, anyway. The two types of inverters function quite differently: the off-grid supplies steady Voltage against varying load demands, the grid-tie supplies whatever amount of current it can make from the panels. Or OG's output varies according to loads, GT's output varies according to supply.

                    I think Windsun is right in that we could use a few more details about what equipment you are using and how it is wired.
                    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                    Ohm's Law: Amps = Volts / Ohms
                    Power Formula: Watts = Volts * Amps

                    Comment


                    • #11

                      Re: DPDT Switch?

                      Re: DPDT Switch?

                      Let me start with what exists today in Ghana, Africa at my missionary friends house:

                      Batteries: 5, 12 v, 198 amp hours each, parallel connection
                      Inverter: AIMS model pwri8k22050 8000 Watt Power Inverter 12Vdc to 220/240Vac 50Hz

                      The batteries are currently charge with an A/C to D/C charger.

                      There are frequent balckouts that can occur during the day and night. They want to avoid the noise of a generator.

                      I am buying 4 Uni-solar 128W/24V flexible panels
                      I think I am still buying the Morningstar TS-MPPT-45
                      Planning on Serial

                      What I am trying to accomplish for them is the following:

                      1) Provide a solar system that will charge the batteries during the blackout thus extending the amount of time power is available to them
                      2) Provide a solar system that will charge the batteries when A/C is on from the street.
                      3) Provide a solar system that can supplement the A/C coming into the house once the batteries are full.

                      1 and 2 are easy. 3 is what I am having difficulty with.

                      My thoughts were to do this:

                      1) Turn the kill switch to the off position from the solar panels
                      2) throw a DPDT switch to transfer all the solar power to a (what type of inverter?) to supplement the A/C power coming into the house
                      3) Turn the kill switch back to the "on" position

                      Is this doable?
                      Last edited by goingtoghana; October 15th, 2012, 10:33.

                      Comment


                      • #12

                        Re: DPDT Switch?

                        Re: DPDT Switch?

                        Looking at what actually exists, it might be easier to shift some AC loads in the house over to the inverter/battery setup than to make changes in the solar panel wiring.

                        You could use a standard AC transfer switch for that and would make the system overall a lot more flexible. That would allow you to just keep the solar panels tied to the battery all of the time.

                        Doing that, whenever you see that the batteries are full, just switch some of the AC loads over to inverter power. That setup would also allow you to just leave the AC battery charger connected all the time also for faster charging when needed.
                        Northern Arizona Wind & Sun Forum & Website Administrator

                        Comment


                        • #13

                          Re: DPDT Switch?

                          Re: DPDT Switch?

                          It would be safe to say I am somewhat familiar with such system needs. It occurs often: unreliable grid power, needs steady supply.

                          Here's how it is normally done: off grid inverter with built-in charger. AC from utility feeds charger and loads when available. When the grid goes down, the inverter immediately takes over loads and batteries are kept charged by solar panels through charge controller.

                          The first thing to do is get a handle on the daily load requirement: peak Watt draw and total Watt hours used. That will tell you what you need for inverter capacity, system Voltage, and battery bank size.

                          This means the AIMS inverter becomes a doorstop, which is the best use that can be made of one. No one in their right mind designs a 8kW 12 Volt inverter! That can draw over 600 Amps if actually pressed to put out its rating (more if you let the Voltage go too low). It's not a good idea at all, no matter what they say. Also it has no built-in charger which is key to making this system work.

                          The second thing that needs changing if at all possible is the five parallel batteries. It is nearly impossible for such an arrangement to share current evenly between the batteries. Some of them will be doing more work than others, resulting in shortened lifespan.

                          I know you have limits on what sort of equipment is available and no doubt a budget as well. So here's another solution utilizing the existing equipment: an AC transfer switch. Something like this one: http://www.solar-electric.com/miso60amp240.html It will allow the loads to be run either by the utility (when available) or the inverter, but it will not be automatic. It will also be necessary to keep the battery charger on the utility directly so that it is never powered by the inverter.

                          Does any of this make sense?
                          1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                          Ohm's Law: Amps = Volts / Ohms
                          Power Formula: Watts = Volts * Amps

                          Comment


                          • #14

                            Re: DPDT Switch?

                            Re: DPDT Switch?

                            And, the MS MPPT 45, IIRC, includes NO Display, and has NO built-in Aux Control function. The MS products often appear inexpensive, until one realizes that the only thing included, is the CC and a manual. OH, you wanted a RTS (Temp Sensor)?? OK that is extra, OH, you need a Display, OK, that, too, is extra. This is the way things have been with MS in the recent past. Doubt that much has changed. Just Opinions. Vic
                            Off-Grid, Sys1: 1280 AH 48 V bat, 5.250 KW STC PV, Classic 150, WBjr, MX-60, MN KID, Xantrex Stacked SW+ 5548s; EU6500isa, 21KW Kubota diesel gens, misc Honda Eu gens
                            Sys2: 1280 AH 48 V 4KS25 Surrettes, 5.88 KW STC, Two Classic 150s, WBjr, MX-60, MN SPDs, Stacked X SW+ 5548s; Kohler 18 KW LP, EU 3000isa gens, HB DC Charger, Midnite Breakers/boxes. Thanks for this great Forum!

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                            • #15

                              Re: DPDT Switch?

                              Re: DPDT Switch?

                              Originally posted by Vic View Post
                              And, the MS MPPT 45, IIRC, includes NO Display, and has NO built-in Aux Control function. The MS products often appear inexpensive, until one realizes that the only thing included, is the CC and a manual. OH, you wanted a RTS (Temp Sensor)?? OK that is extra, OH, you need a Display, OK, that, too, is extra. This is the way things have been with MS in the recent past. Doubt that much has changed. Just Opinions. Vic
                              Accurate opinion in my opinion. By the time you add on all the "extras" you might as well buy the MidNite Classic in the first place.
                              1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                              Ohm's Law: Amps = Volts / Ohms
                              Power Formula: Watts = Volts * Amps

                              Comment

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