Need advice on inverter connection !!

Roadrunner
Roadrunner Registered Users Posts: 10 ✭
in Solar Beginners Corner #1
Hello everyone !
Can the output of an inverter running from solar charged batteries be synchronized with the mains supply such that the inverter will power the AC loads as much as it can , and the remaining will come from mains?

I am using a dpdt relay activated by mains. I connected the NC to inverter output and did not connect anything to NO.
Then I connected the load and mains to COM.
Now, in the inactive state of relay the inverter will supply power to the loads. But at the same time, mains are also connected to the load.
The batteries were fully charged at this point.
The inverter alerted about short circuit. ( because inverter output has got connected to mains?? )

How to go around this problem?
Thank you :)
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Comments

  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #2
    Re: Need advice on inverter connection !!
    Roadrunner wrote: »
    Hello everyone !
    Can the output of an inverter running from solar charged batteries be synchronized with the mains supply such that the inverter will power the AC loads as much as it can , and the remaining will come from mains?

    I am using a dpdt relay activated by mains. I connected the NC to inverter output and did not connect anything to NO.
    Then I connected the load and mains to COM.
    Now, in the inactive state of relay the inverter will supply power to the loads. But at the same time, mains are also connected to the load.
    The batteries were fully charged at this point.
    The inverter alerted about short circuit. ( because inverter output has got connected to mains?? )

    How to go around this problem?
    Thank you :)

    There are only two kinds of inverters which can be coupled to an active mains supply.
    One is a grid-tie inverter which will run directly from the panels without batteries and deliver all of the power from the panels into the mains connection, to go either to your loads or at least in part, back to the utility.
    The other is a hybrid inverter, with batteries, which includes the option to sell power back to the utility or supply that power to your loads based on the state of charge of your batteries and the amount of power that the PV is producing.

    If you do not have one of these two specialized inverter types, there is no way around the problem. Your inverter is not capable of synchronizing its output to the mains supply voltage and frequency.
    SMA SB 3000, old BP panels.
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  • Roadrunner
    Roadrunner Registered Users Posts: 10 ✭
    #3
    Re: Need advice on inverter connection !!

    Thanks for the input :-)
    But isn't there any way to modify my inverter by adding some kind of synchronizer?
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Need advice on inverter connection !!
    Roadrunner wrote: »
    Thanks for the input :-)
    But isn't there any way to modify my inverter by adding some kind of synchronizer?
    In a word, no. This capability has to be designed into the inverter from the start.
    SMA SB 3000, old BP panels.
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  • tallgirl
    tallgirl Solar Expert Posts: 413 ✭✭
    #5
    Re: Need advice on inverter connection !!
    inetdog wrote: »
    In a word, no. This capability has to be designed into the inverter from the start.

    It could be modified by throwing it in the trash. That would be one modification that would work.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,023 ✭✭✭✭
    #6
    Re: Need advice on inverter connection !!

    She's baaack! Long time no see Julie. How goes business?
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #7
    Re: Need advice on inverter connection !!
    Roadrunner wrote: »
    Thanks for the input :-)
    But isn't there any way to modify my inverter by adding some kind of synchronizer?
    As others have said, no, you can't. Even if you were an electrical engineer and came up with a functioning modification, your fiddling with the guts of the inverter would void its UL listing, and connecting it to the grid would be a code violation and a violation of whatever interconnect agreement you could get from your utility.

    Speaking of interconnect agreements with the utility - you aren't trying to connect your inverter to your service without one, are you? That would be a good way to get your service shut off.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #8
    Re: Need advice on inverter connection !!
    Roadrunner wrote: »

    The inverter alerted about short circuit. ( because inverter output has got connected to mains?? )

    How to go around this problem?
    Thank you :)
    You get around it by never having it connected at the same time the mains are connected. Basically it's like a generator not meant to be back fed with power. You also might be having a problem with the Neutral - Ground bond in the Inverter.
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  • Roadrunner
    Roadrunner Registered Users Posts: 10 ✭
    #9
    Re: Need advice on inverter connection !!

    blackcherry04, exactly !

    I realize my mistake now. :)
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  • Roadrunner
    Roadrunner Registered Users Posts: 10 ✭
    #10
    Re: Need advice on inverter connection !!

    one more doubt..please have a look..
    If I charge my batteries with solar ( via charge controller) and mains ( via home inverter) simultaneously , how will the battery bank decide how much current to take from solar/mains?
    Or will both currents simply add up?
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
    Re: Need advice on inverter connection !!

    they add up so be sure any batteries can tolerate both charge sources at the same time.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #12
    Re: Need advice on inverter connection !!

    With enough components and enough time you can get a GTinverter to be syncd to a battery powered inverter. I have done it. BUT there always is a "but". it took me 3 x1500w GTinverters and another 3 x1000w TSW inverters. They all ended up in scrap bin. but the 4th set worked ok.
    There are two things you have to modify . One is the frequency has to be slightly different between them and secondly one has to have a slightly higher output voltage than the other.
    Now its not much use giving more info. because there is no possibility of any 2 inverters having same topology. So you have to do it by trial and error,. And have a good understanding of how inverters are laid out and the function of each section of circuitry.
    And it even better if someone else is paying for the inverters.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #13
    Re: Need advice on inverter connection !!

    Niel that is not really true . Well I have never found it to be that you get the max output from the solar charger and the mains charger.. I have always found one tends to dominate the other. This is because all chargers have slightly different charging patterns. example one may cut its output to half aprox at 80% battery charge and the other one at 90%.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #14
    Re: Need advice on inverter connection !!
    Roadrunner wrote: »
    one more doubt..please have a look..
    If I charge my batteries with solar ( via charge controller) and mains ( via home inverter) simultaneously , how will the battery bank decide how much current to take from solar/mains?
    Or will both currents simply add up?
    It depends on how you have them setup. if you want to get as much out of the solar, you set it up a little higher so it becomes the dominate source. In Bulk they will both put out the maximum, once they get to Absorb and the batteries accept less current the Grid Charger will back off and the Solar source will finish the charge. It's a little trial and error, to get the voltages right.

    Example : I have a 1100 Amp hr bank, I have a 150 amp grid charger and 70 amp's of solar. I have the Grid charger set to 14.4 V absorb and the Solar set to 14.8 absorb. If I left the Grid Charger fighting with the Solar it would be a waste of money and the batteries are only going to accept what they will anyway. The grid charger is on a timer also, it will only bulk early in the morning because of the time and once it gets to 14.4 V it will take it's self out as the Solar over rides it, it's worked great for years.
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