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  • Inverter & Generator mismatch

    Just inherited an off grid system - has nice batteries that I would like to keep in good shape. Preparing for winter and possibility of many days with no sun so need generator. Problems seem to be that the inverter (aims 10k 48 volt) and the generator (generac 7.5k Power pac) are mismatched. Not enough power from the genny. Tried turning off house supply when charging and turned down the rate of charge to just under 10% still no joy - gen charges for 10 mins then inverter cuts it off.
    So question is - how do I match or correct without breaking the bank. My thoughts are new dc generator (haven't found anything reasonable) new inverter.

    Battery array is 2 strings of Trojan SPRE 06 415 giving me 20hour 740amp - House usage is 6 kwh per day max and i have 2 surge appliances (well pump and refrigerator)

    Any thoughts on dc generator or sizing (and make) of inverter would be greatly appreciated.

    Regards Father Bob.

  • #2
    Hi Father Bob

    It is hard to determine your needs with the information you have provided. Most generac generators output AC voltage so I am not sure how you are using it and the inverter.

    Can you send a wiring diagram on how the components are put together?

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    • #3
      This is an old diagram - ignore the batteries - they are now 16 Trojan SPRE 06 415 wired in 2 serial strings which are paralleled Solar Layout.pdf

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      • #4
        After reading your response - yes the generac power pact is a 2 phase AC generator, they are not normally used for off grid and it voids their warranty, so moving up to a 10kw or greater ac generator will have the same warranty problem. So if I am changing generators I would seriously consider DC generator to charge batteries as i believe that is what they are designed for

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        • #5
          Based on that diagram it looks like that generac has a 48V output which then is converted to 240V by the inverter. But I am not sure why there is an arrow from the power breakers to the inverter. It should only be from the inverter to the power breakers.

          Also I am assuming that you are using a breaker in that "box" of power breakers which is wired between the Outback CC and the batteries. If not then you might have an issue there.

          Are you getting any error messages on the inverter as to why it is shutting down? It is possible that you have the batteries not connected to the proper "charging output" of the inverter.
          Last edited by SunEagle; 09-16-2019, 11:10 AM.

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          • #6
            Originally posted by Father Bob View Post
            After reading your response - yes the generac power pact is a 2 phase AC generator, they are not normally used for off grid and it voids their warranty, so moving up to a 10kw or greater ac generator will have the same warranty problem. So if I am changing generators I would seriously consider DC generator to charge batteries as i believe that is what they are designed for
            If that inverter is not capable of charging your batteries from a generator I would look into getting a separate battery charger that will work with your generator to charge the battery system.

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            • #7
              Sorry for the "rough" diagram - yes the connection box has breakers for battery and house feeds. The connections are all OK. The problem I am facing with the mismatch is that the inverter is 10kw and the generator is 7.5 kw (therefore underpowered by 2.5 kw) and the inverter does not like it.
              So to remedy the problem I need to change something - I am leaning toward a new generator as I stated before the Generac is not rated for off grid and seems to be a little tired. Any ideas on a 48 volt LP Generator?

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              • #8
                Originally posted by Father Bob View Post
                Sorry for the "rough" diagram - yes the connection box has breakers for battery and house feeds. The connections are all OK. The problem I am facing with the mismatch is that the inverter is 10kw and the generator is 7.5 kw (therefore underpowered by 2.5 kw) and the inverter does not like it.
                So to remedy the problem I need to change something - I am leaning toward a new generator as I stated before the Generac is not rated for off grid and seems to be a little tired. Any ideas on a 48 volt LP Generator?
                Maybe Cummins/Onan or Kohler has what you need.
                Last edited by SunEagle; 09-16-2019, 11:30 AM. Reason: modified info

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                • #9
                  Originally posted by Father Bob View Post
                  Just inherited an off grid system - has nice batteries that I would like to keep in good shape. Preparing for winter and possibility of many days with no sun so need generator. Problems seem to be that the inverter (aims 10k 48 volt) and the generator (generac 7.5k Power pac) are mismatched. Not enough power from the genny. Tried turning off house supply when charging and turned down the rate of charge to just under 10% still no joy - gen charges for 10 mins then inverter cuts it off.
                  So question is - how do I match or correct without breaking the bank. My thoughts are new dc generator (haven't found anything reasonable) new inverter.

                  Battery array is 2 strings of Trojan SPRE 06 415 giving me 20hour 740amp - House usage is 6 kwh per day max and i have 2 surge appliances (well pump and refrigerator)

                  Any thoughts on dc generator or sizing (and make) of inverter would be greatly appreciated.

                  Regards Father Bob.
                  Bigger inverters don't trip out from smaller generator...there is something else the matter. Find what's really the matter before throwing any money at it....

                  If you want real proof go and rent a 10 kW genny at rental store and come back here with the results.
                  Last edited by neweclipse; 09-16-2019, 01:00 PM.

                  Comment


                  • #10
                    Originally posted by Father Bob View Post
                    ...... The problem I am facing with the mismatch is that the inverter is 10kw and the generator is 7.5 kw (therefore underpowered by 2.5 kw) and the inverter does not like it......
                    The first problem is AIMS. I do not believe in their products at all. However, that aside, the "generator" is not mis-matched.
                    I run a 6kw inverter and charge in winter with a 3kw generator , and it works, because it's configured properly. I even ran for a week off a honda eu2000 at night while rebuilding my battery bank, inverter never complained.
                    In the winter, I get along with running the generator for 90 min daily, in the the worse conditions.

                    Learning to use the gear, and program it for different conditions, is what allows things to work properly.

                    Most likely the easiest way to solve this, is to obtain a 240VAC powered, 48V golf cart charger, and power it from the generator. Getting 30 or 40 DC amps into the battery, and it would look just like the sun is shining, for all the inverter cares about.

                    In cloudy weather, you need to manage your loads so you don't deplete your batteries, which translates in to shorter generator run times. You need a clamp on DC ampmeter, to read the amps the batteries are being charged with, and when the batteries are charged enough they are only drawing 10 or 15A from the charger, you can let the generator cool down and shut it off


                    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

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