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  • Sizing well pump inverter (first post)

    My load is a 1hp, 230v 3 wire, deep well pump. (goulds 7gs10 to be exact). This will be my largest load so I am trying to calculate the size of the power inverter to match. From the spec sheet the following: Rated input, each leg 8.2 amps, 1200 watts. Maximum input, each leg 9.8 amps, 1600 watts. Locked rotor amps is 41.8. Am I correct in calculating the max running watts as (9.8*2)A*230V = 4508? I understand that there is a surge, or starting load, but I'm not sure how to find the values. Locked rotor amperage*voltage is 9614 which seems unlikely. Any thoughts on where my calculations go wrong? Thanks.

  • #2
    Originally posted by jtbartlett View Post
    My load is a 1hp, 230v 3 wire, deep well pump. (goulds 7gs10 to be exact). This will be my largest load so I am trying to calculate the size of the power inverter to match. From the spec sheet the following: Rated input, each leg 8.2 amps, 1200 watts. Maximum input, each leg 9.8 amps, 1600 watts. Locked rotor amps is 41.8. Am I correct in calculating the max running watts as (9.8*2)A*230V = 4508? I understand that there is a surge, or starting load, but I'm not sure how to find the values. Locked rotor amperage*voltage is 9614 which seems unlikely. Any thoughts on where my calculations go wrong? Thanks.
    1. Normal power is just 8.2 x 230. You are adding in an extra factor of two.

    2. The starting amperage (except maybe for the first fraction of a cycle) will be less than or equal to the locked rotor amperage. Fortunately not all of that current will be in phase with the source voltage so the power required, in watts, will be somewhat lower than the product of volts times amps.

    3. But the inverter or generator which has to start the motor will need to be able to supply at least half of that current to get the motor going.
    With a generator you have the inertia of the rotating system to help handle the surge even though the windings of the generator may not be able to carry that load for more than a minute or two.
    With an inverter, the batteries have to be able to supply the full surge current and the output circuit of the inverter has to be able to handle it for at least a few seconds without overheating.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Originally posted by inetdog View Post
      1. Normal power is just 8.2 x 230. You are adding in an extra factor of two.

      2. The starting amperage (except maybe for the first fraction of a cycle) will be less than or equal to the locked rotor amperage. Fortunately not all of that current will be in phase with the source voltage so the power required, in watts, will be somewhat lower than the product of volts times amps.

      3. But the inverter or generator which has to start the motor will need to be able to supply at least half of that current to get the motor going.
      With a generator you have the inertia of the rotating system to help handle the surge even though the windings of the generator may not be able to carry that load for more than a minute or two.
      With an inverter, the batteries have to be able to supply the full surge current and the output circuit of the inverter has to be able to handle it for at least a few seconds without overheating.

      So, my operating voltage is 8.2*230= 1886 and maximum (s.f.load) is 9.8*230= 2254. That sounds better. However, starting amperage will be >.5*(41.8*230)=4807. There will probably be occasional, concurrent house loads. SO... I am probably looking at a 6kw (+) inverter (?). This seems larger than I had originally thought but this is the one load that I cannot control - pump is down the hole at 480' and not coming out again until it dies. This is 48v, offgrid application.
      I have been trying -unsuccessfully- to find a way to run this load with smaller equipment. Cistern pumping/ gravity feed is not possible due to topography and climate.

      Comment


      • #4
        I have a 1/2 hp deep well pump, that consumes 1,000w @ 240V when running (pumping 160'). As reported my my inverter's control panel.

        I would expect a 1hp pump to consume about 1800W @ 240V. You get a little better efficiency with larger gear.


        Your locked rotor power of 42A @ 240V would be 10,080 watts, a bit of a strain for most inverters and battery & cable systems.
        What does work in your favor, is the long wire going down the well, that resistance will reduce the peak the motor will pull.

        US systems are 60hz, 240V. 230V is not a standard household voltage.

        I can state that my lights don't even blink when my pump kicks on. (Xantrex/Schnider XW-6048, 6Kw, 48V)

        If you have an above ground tank, you can pump 500 gallons to it in the daytime, when you have sun (unlimited power) and use a [B]much [/B]smaller pump to pressurize your water for night time use, instead of the 1Hp pump kicking in 4 times a night, sucking the batteries down.
        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
          I pulled the 230v off of the Franklin motor spec sheet. Not sure why its 230 but that's what it says. My static level is 261' and the hole is 500' with a pump hung at 470'. Unfortunately for me, a 1/2 hp motor doesn't cut it.I have resigned myself to the fact that this isn't going to happen with an inverter and that I will have to fill a bulk tank under generator power. An outside tank is not possible, winter is too cold and long. An underground tank is not possible, 20"to bedrock. So...it's going to be inside, under the stairs. Also I just noticed the post under DC pumping (sorry). Would I be better off using a DC pump to pressurize the house tank or is it easier to just stay with AC. I understand there are losses and such but I'd probably need a DC>DC converter. Similar losses? Also, what sized pump is suitable for this application? My load calculations just went out the window with the pump changes. I don't have a real good idea how much water we actually use so it's a bit tough to tease out the specifics. I'd bet we're under 200 gallons a day without conservation. Is there any additional strain on the well pump using a generator to pump up a bulk tank? The cycling will be drastically cut so that's probably good. Does a well pump need pure sine or will AVR hurt it in the long run?

          Any thoughts on sizing a generator to run a 1hp pump with ~10k surge? My box store troy bilt 7500/10500 strains heavily when the pump is turned on. I'd love to have an ISUZU driven 12k diesel but it's tough to justify the 6k price just for a well pump! Thanks for any help possible. Sorry if this seems a bit scattered but I just made the decision today to ditch the inverter driven pump. I would need waaay too much of a system for just 1 load and the rest of the time it would be waste, nice to have, but waste. Thanks

          Comment


          • #6
            Originally posted by jtbartlett View Post
            I pulled the 230v off of the Franklin motor spec sheet. Not sure why its 230 but that's what it says.
            A 240 volt ac motor will have a spec of 230 volts. This is to account for line loss. For engineering and design purposes the code is different for motors. Normally you standard circuit the conductor is based the breaker size. Not so with motors and transformers.
            MSEE, PE

            Comment


            • #7
              If you want to run a large pump, you need a large inverter or a large generator. You can stack a couple 40 gal pressure tanks to stretch your water time, but running a generator 3x a day for 10 minutes of pumping, will kill the genset from cold running. You may be better off biteing the bullet for the big inverter, several pressure tanks, and save the genset for foul weather battery charging.
              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


              • #8
                I know for a fact that a good quality 3500 watt genset will start and run up to a 1.5 HP pump (Honda EG3500). It's also a good thing that you have a 3-wire as a 2-wire consumes 2x the start power (per Franklin). For an inverter you should try about a 5K. There was another poster (don't remember the forum) who had similar questions and he got his inverter to successfully start his pump.

                When you do need to change the pump look into the Grundfos SQ, which has a built-in soft-start and a much more efficient motor. They are available in up to 1.5 HP.

                Comment


                • #9
                  Similar thread with results:

                  http://forum.solar-electric.com/show...00-watts-solar!

                  Comment


                  • #10
                    1. If you are dead set on not replacing the pump (which I can sympathize with), then look at getting a full Variable Frequency Drive (VFD) or at least a solid state soft start aid. That will allow you to get by with the smallest possible inverter.
                    2. If this is a centrifugal (impeller) pump, which it almost certainly is, you should start the pump against a closed valve to minimize the power required as the pump accelerates up to speed. Then after a few seconds automatically open the valve slowly. This will also minimize the starting surge requirements.
                    SunnyBoy 3000 US, 18 BP Solar 175B panels.

                    Comment


                    • #11
                      Thanks for the replies. For now I am going to run what's down the hole. The make or break switch would work great if this was an irrigation pump but it's a non starter for a household pump. The difference between the grundfos pump and the 1hp I have was exactly $1719. Hopefully I won't be paying this out on the other end in solar equipment. Do I regret not spending it upfront? a little, but if I can use quality equipment that will work I won't regret it for too long. I am hoping something like a Xantrex 6048 inverter will make things work. I am planning on a 560AH battery bank for the house but will I have problems with power spiking during the surge current? I do not know what the weak point is regarding the start current through the inverter. The pump will run for less than 40 minutes a day total and the household budget is 5k watts. Am I making an error in sizing the batteries specifically regarding the pump which is the largest load? Thanks again for the help.

                      Comment


                      • #12
                        Originally posted by Texas Wellman View Post
                        I know for a fact that a good quality 3500 watt genset will start and run up to a 1.5 HP pump (Honda EG3500). It's also a good thing that you have a 3-wire as a 2-wire consumes 2x the start power (per Franklin). For an inverter you should try about a 5K. There was another poster (don't remember the forum) who had similar questions and he got his inverter to successfully start his pump.

                        When you do need to change the pump look into the Grundfos SQ, which has a built-in soft-start and a much more efficient motor. They are available in up to 1.5 HP.
                        Do you mean a 5k inverter with 10k surge capacity? I guess I don't understand how the EG3500 can start a 1.5 hp pump. The locked rotor amps would have to be lower than the max AC output of the generator? 29.8A? I would thing the larger motor would be more difficult to start. I got the 3 wire pump and the cap/start cap/run for the lower starting power requirement, although, I'm not sure it matters terribly looking at the start requirements of the pump.

                        Comment


                        • #13
                          Originally posted by jtbartlett View Post
                          Thanks for the replies. For now I am going to run what's down the hole. The make or break switch would work great if this was an irrigation pump but it's a non starter for a household pump. The difference between the grundfos pump and the 1hp I have was exactly $1719. Hopefully I won't be paying this out on the other end in solar equipment. Do I regret not spending it upfront? a little, but if I can use quality equipment that will work I won't regret it for too long. I am hoping something like a Xantrex 6048 inverter will make things work. I am planning on a 560AH battery bank for the house but will I have problems with power spiking during the surge current? I do not know what the weak point is regarding the start current through the inverter. The pump will run for less than 40 minutes a day total and the household budget is 5k watts. Am I making an error in sizing the batteries specifically regarding the pump which is the largest load? Thanks again for the help.
                          My old tired battery setup of 400ah PbH2So4 and the XW6048 started the 1/2 hp pump fine, and ran welder and air compressor fine.

                          You mention 40 minutes run time, is that 1 start cycle, or several throughout the day/night ? If daytime, the PV will pick up the load and the batteries just level it out.

                          The chart in the XW-6048 manual indicates that for 10 seconds, it can supply just over 50A , the 4548, right at 40 amps on the AC output.
                          http://www.solar-electric.com/lib/wi.../XW-manual.pdf sheet 103, pdf page A-3
                          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


                          • #14
                            The pump starts will be for household usage, so multiple starts to refill pressure tank drawdown. Probably a few starts in the morning, nothing during the daytime and again heavier in the evening. The 4548 is just shy of what we need and with other loads running concurrently it might not work so well. Is there any problem using an inverter that's a bit too large for the rest of the household needs? We don't really need a 6k inverter except for the one load. The rest of the time it probably will not exceed 3k or so. I don't think the tare losses between the 4548 and he 6048 are significant.

                            Mike, just curious what welder you are using with PV? I had basically written off using a welder without generator support.

                            Comment


                            • #15
                              You have the Grundfos SQ confused with the SQ Flex. The Flex is the solar pump, the SQ is the regular pump.

                              The difference is that the SQ only accepts AC power and has a built-in soft-start that plays very nicely with inverters (no start surge). The SQ Flex will accept either AC or DC. You can buy a SQ for under $1,000 easy on-line, just do a search.

                              Originally posted by jtbartlett View Post
                              Thanks for the replies. For now I am going to run what's down the hole. The make or break switch would work great if this was an irrigation pump but it's a non starter for a household pump. The difference between the grundfos pump and the 1hp I have was exactly $1719. Hopefully I won't be paying this out on the other end in solar equipment. Do I regret not spending it upfront? a little, but if I can use quality equipment that will work I won't regret it for too long. I am hoping something like a Xantrex 6048 inverter will make things work. I am planning on a 560AH battery bank for the house but will I have problems with power spiking during the surge current? I do not know what the weak point is regarding the start current through the inverter. The pump will run for less than 40 minutes a day total and the household budget is 5k watts. Am I making an error in sizing the batteries specifically regarding the pump which is the largest load? Thanks again for the help.

                              Comment

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