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  • Need off grid split phase for well pump

    I have a 240v well pump that is 3/4 HP. I am assuming it needs 750watts -- but I'll double that to 1500, and round it up to 2000w just in case.

    I have several solar panels (35v 300w). I have a 2000w "240v Grid Tie" "_inverter_", that is rated at the voltage for my panels. However I understand it only works if there is a grid, because it requires a reference wave (USA 240v 60hz split phase).

    I understand I can use my 240v grid tie inverter, if I had a grid. It would only save on my bills. That would probably be fine.

    However I am trying to see if there is a cheap option to run off grid, or in case of an emergency, the well pump for my irrigation field. I could buy a 240v gas generator, and use it as a reference, I believe would save on gas. (?)

    But is there a product that will generate a 240v reference split phase, and I could daisy chain these grid ties? It isn't clear to me what a Microinverter is (does that also require a grid reference frequency? there is so much spam on the internet I can't figure it out).

    Is there a cheap 240v USA inverter that is only 200-300 watts (cheap s in $<200) that I could use a reference wave?

    what the heck is a microinverter in terms of all of this any. Thanks

    Also, I read about 12v well pumps, there is no safe way to run 12 or 24v 250ft down to the pump. Why does this product even exist



  • #2
    Originally posted by danos View Post
    I
    Also, I read about 12v well pumps, there is no safe way to run 12 or 24v 250ft down to the pump. Why does this product even exist
    Why do you think there's no safe way to run 24V down to a pump?
    The one I see is not for 250' deep, but rather only 100' submersed and max 230' lift.
    So if your concern was about voltage drop, I think that's something that could be accomplished. 6AWG wire going 100' deep and ~50' on the surface with a 5A current and 24V would be ~0.6V of voltage drop, (2.47%)

    However I am trying to see if there is a cheap option to run off grid, or in case of an emergency, the well pump for my irrigation field. I could buy a 240v gas generator, and use it as a reference, I believe would save on gas. (?)
    You'd also have a very good chance of frying the generator.
    You're worried about a 24V pump not being safe? This is a much less safe idea.
    When the pump shuts off, what happens with the extra power being supplied by the solar panel's inverter? It goes INTO the generator and bad things happen.
    And how would you hook up this bad idea? The possible choices I can see - like a double-male-end extension cord - is a really unsafe and horrible idea.

    But is there a product that will generate a 240v reference split phase, and I could daisy chain these grid ties?
    Not really.
    There's off-grid or hybrid options - but it's likely a generator to run the pump is much cheaper.
    One inverter manufacturer has an option for a 110V outlet powered by solar when disconnected (they name it "Secure Power Source")

    It isn't clear to me what a Microinverter is (does that also require a grid reference frequency?
    A microinverter is basically the same as your regular inverter - but much smaller scale.
    Your 2kW inverter takes a bunch of panel's power and changes it to AC.
    A microinverter takes a single panel's power and changes it to AC.

    Comment


    • #3
      foo1bar, a grid tie inverter is different than a regular standalone PWM or pure sine wave inverter. A grid tie inverter synchronizes to a grid and won't work without a source. Did you know this? How would it damage the generator? The generator would just throttle down to idle unless there was a cloud.

      a 24V 6 amp pump would only be 120watts. I don't think it would have the lift

      a 750w pump at 24v, and at 100ft would have a 10% voltage drop would need 31 amps. my plasma cutter on high is 50amp. that just seems to be bad.

      so, is a microconvert a standalone inverter and does not need a source to synchronize with? That might be all I need because I see them on ebay for about $120.

      Comment


      • #4
        Originally posted by danos View Post
        foo1bar, a grid tie inverter is different than a regular standalone PWM or pure sine wave inverter. A grid tie inverter synchronizes to a grid and won't work without a source. Did you know this? How would it damage the generator? The generator would just throttle down to idle unless there was a cloud.
        That is not how it works. A grid tie does not need a reference , it needs a GRID. A genrator is not a grid and it will not work like you think.

        You also can not since a large grid tie to a tiny lille cheap ass 200w inverter. Of for some ungodly reason all the safeties failed and it did sync
        That little 200w inverter becomes a molten pile of slag. what you are talking about is AC coupling and it is expensive and complex and requires a bimodla inverter that is larger than the grid tie, and a battery bank that is also large enough to take the full charge.

        you could do a cheaper and safer job with just the bimodal inverter or decent off grid inverter.
        OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

        Comment


        • #5
          thanks this is helpful.


          What if I get one of these 1400w microinverters for $119 and hook it up to ~60v of series of 100Ah battery, and hook up MPPT solar to the battery bank will it generate 240v for my well pump? The well pump is full on for the entire day to fill a 10,000 gallon tank for irrigation. How do these work? Can it I just run one solo? Does this make sense, am I communicating this correctly?


          https://www.ebay.com/i/143213698038?...3D143213698038

          Comment


          • #6
            Originally posted by danos View Post
            I have a 240v well pump that is 3/4 HP. I am assuming it needs 750watts -- but I'll double that to 1500, and round it up to 2000w just in case........
            You assume wrong. you are assuming perfect efficiency, which is only the textbook value, not real world.

            I have a 1/2 hp pump. it consumes right about 1kw according to my inverter's internal meter system (it's accurate)
            The issue is this is not watts in AC, it's Volt Amps VA. VA takes into consideration the effects of inductive circuits (like motors) and how they pull power "out of phase" where the inverter has to work extra hard to make the power demand. LED lights, ceiling fans, and fridge motors have a Power Factor PF rating and that can be used to roughly calculate actual draw.
            Here is a chart for a popular brand of well pump motors:

            Well Pump Motor Specs.jpg

            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 danos View Post
              thanks this is helpful.
              What if I get one of these 1400w microinverters for $119 and hook it up to ~60v of series of 100Ah battery, and hook up MPPT solar to the battery bank will it generate 240v for my well pump? The well pump is full on for the entire day to fill a 10,000 gallon tank for irrigation. How do these work? Can it I just run one solo? Does this make sense, am I communicating this correctly?
              NO it will not. Micro inverters are grid tie inverters NOT off grid and not bimodal.
              They are also not designed to connect to a battery. They ARE designed to take as much power as comes in and inverter it ALL as FAST as possible to feed the grid.

              You need to get an off grid inverter or bimodal inverter
              OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

              Comment


              • #8
                Why not just replace the pump? Grudfos SQ flex seems like it will fit your needs. "The motor can operate under any voltage from 30 - 300 VDC and 90 - 240 VAC"

                Comment


                • #9
                  I have the cheap option to run my well and anything else without the grid, its a 5 KVA generator.
                  The most practical way to run a deep well off grid might be a DC well motor and the battery plant
                  to deal with it. This will be far, far from cheap. Bruce Roe

                  Comment


                  • #10
                    yes thank you. I thought microinverters were actually grid tie!

                    my next question, when I was 10 years old I asked my dad why couldn't you just take a motor and hook the output shaft to a generator, plug the motor in, then realllly quickly unplug the motor from the wall and into the generator and it would run indefinitely with free electricity. Of course my dad told me, no you cannot do that be the Law of Thermal dynamics and he said that would be called a perpetual motion machine. To this day there are thousands of people on youtube who believe what I thought at 10 years old is possible and refuse to understand basic physics that have millions of subscribers, and there is absolutely nothing that will convince them.

                    Now I am in my 30s and my question is... if I take a motor, and hook it up to a generator. ... and have a flywheel in between to store some of the momentum force... and also hook up a Grid Tie inverter to this... Start the motor with the grid or gas engine.... make sure the grid tie inverter is connected to the system. Then ... really fast disconnect the motor from the grid/gas, and plug it into the grid tie inverter, would this run indefinitely (until a cloud comes)? Basically fool the grid tie inverter by having a reference grid and then switching it to itself with a motor-generator. Would I be able to use the enegry from the grid tie inverter minus what the motor-generator-reference frequency?

                    The problem is I need to run the well pump for irrigation and it runs constantly 24/7 to fill a tank. In the summer it would run 100% everyday. Given there is no sun at night, during the day. If I were to run a gas generator 24/7 for 90 days in the summer, it probably wouldn't last long and we're talking $30 in gas everyday ($2700 at $3/gallon)

                    Comment


                    • #11
                      Originally posted by danos View Post
                      a 24V 6 amp pump would only be 120watts. I don't think it would have the lift
                      One example:
                      https://www.toboaenergy.com/product/...-pump-24vdc-2/

                      Their table says
                      140' lift takes 3.1A and delivers 99GPH
                      100' lift takes 2.6A and delivers 103GPH

                      It obviously isn't enough to provide water and presure for a center pivot irrigation for a 40 acre field.
                      But I don't think that's your design goal anyhow.

                      Most economical solution for running when lines are down due to storm (or whatever) is probably a generator.

                      I'd start by looking at that cost for what you want. Then see if there's any other solution you can come up with that gets close to that for reliability and cost.

                      Comment


                      • #12
                        Originally posted by danos View Post
                        yes thank you. I thought microinverters were actually grid tie
                        They are grid tie.

                        Basically fool the grid tie inverter by having a reference grid
                        You're not going to easily have a reference that will fool the grid tie inverter.
                        If the reference varies in voltage too much the inverter will know it's not real and shut down.
                        To build a sufficiently robust reference you've probably spent enough money to have a bimodal or off-grid system (probably way more than enough)

                        Comment


                        • #13
                          One solution is just commission a grid tie system, running the AC pump off the grid for about
                          breaking even on energy? There is no free lunch, Jan 2018 my well developed an internal
                          leak and ran up some huge electric bills, before I realized it was not just heating the house.
                          Several panels will not begin to deal with such things in the real (seasonal. cloudy, variable day)
                          world.

                          There are so many things wrong with your proposal, I am not going to try and itemize them. If
                          you have a digital storage scope (and know how to use it), take EE101, then another on motors,
                          another on switching converters, and perhaps one on grid tie inverters, and have lots of
                          expendable parts to experiment with (before the smoke gets out), and can do it without hurting
                          yourself or burning anything down, you might be in a position to take on the design problem.
                          good luck, Bruce Roe

                          Comment


                          • #14
                            You could take the route I took, which I have been very pleased with. I have a storage tank about 150 vertical feet higher than my cabin. It provides 24/7 pressurized water on demand though I only run my water pump during daylight hours. I installed a Schneider XW+6848 inverter with a 48V Trojan battery bank powered by 15 300watt Renogy panels. I can run the pump from about 8:30 am till 4:30pm because my panels are mounted on pole-mounts that can be rotated to face the sun. Since you have a smaller pump, you could make it work with Renogy's 3600W cabin kit. Get a XW+5548 or XW+6848 and it will work. You might get it to work powering it with a SW4024/SW4048, but that's pushing those inverters close to their limits. It's worked for two years now, watering my 100 tree orchard. Outback's Radian line should also be looked at.

                            There are also high voltage DC Grunfos water pumps you can buy that run at up to 240VDC. Wire eight grid-tie panels in series for 240VDC, and you'll have a pump that will equal what you have in the ground now.
                            Last edited by MichaelK!; 04-23-2019, 08:03 PM.

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                            • #15

                              If even accurate, your calculated fuel cost of $2700.00 for 24/7 90 days is your best clue as to the magnitude of this under-taking...
                              Assuming no multiple daily stop and start and strictly using available daily sun, to pump to a 10,000 gallon storage with only having gravity discharge flow to irrigation, I'd say this...
                              Forget free perpetual motion energy, forget AC, or any battery usage. Just use a big enough DC pump and as many solar panels as required to meet you average production day to day

                              K.I.S.S. avoid unnecessary added costs and all losses and inefficencies thru useless conversions.
                              Last edited by neweclipse; 04-25-2019, 12:31 PM.

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