Combining Multiple AC Inverter Supplies

Discussion in 'Power Electronics' started by Brendon Drew, Sep 19, 2016.

  1. Brendon Drew

    Thread Starter New Member

    Sep 19, 2016
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    I have been doing some research but it seems there is not alot of infomation.

    I have at the moment a single power inverter in a car, 12vDC in and 240vAC @ 600W

    If i wanted to say have 1200W but had 2 600w inverters can i combine the AC outputs the same as you would in DC?
    Im not sure, would the sine waves need to be in sync?

    Any help is great

    cheers,
    brendon
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Welcome to AAC
    In short it is dangerous. One or even both might blow.
    However you can IF the two inverters are from same manufacturer and IF they say they can be paralleled. They can if the units are designed that way.
    If not, DO NOT DO IT.
     
  3. tcmtech

    Well-Known Member

    Nov 4, 2013
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    No you can't.

    The internal clock systems that dictate what output frequency they run at have to be synchronized and that's not something that anyone can do with inverters that are not designed for that sort of application.

    If you need more power buy a bigger inverter.
     
  4. Brendon Drew

    Thread Starter New Member

    Sep 19, 2016
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    cheers for the straight answer guys, actually does help. I figured that would be the case
     
  5. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hi,

    Sine waves are interesting in that they are unlike other waves because they can be added.
    This makes for all sorts of configurations, the simplest would be series or parallel.

    In series, each converter provides 1/2 the voltage level and if the phase is shifted then the voltage can be adjusted. For converters that have fixed output though, the two waves have to be in parallel and that means they have to be in sync. There is some wiggle room because of impedances, but not much. In general, the two converters would have to be made to be connected in parallel. That means that the manufacturer would have had to design them with the parallel configuration in mind. If not, it's not going to work at all.

    Back when i worked in the industry we worked with low to high power units, as high as 30,000 watts. That's a lot of watts. Some of them used two or more H bridges to drive heavy output transformers. In all cases however, the reference frequency came from either a single crystal based osillator or a single variable frequency oscillator. Each bridge was driven in sync so that they all produced the same output phase. That's the most important part. If one is out of phase it could draw current from the other H bridge which is bad, or supply current to the other H bridge which is also bad. It would not work for long that way.

    So long story short, if you need 1200 watts then you have to buy a 1200 watt unit, but then again we also had a saying way back then that referred to the output at full load, and that is, we called it, "FOOL LOAD". Amusing but true, and that of course was a play on words as a replacement for "FULL LOAD" which means that if you want 1200 watts then you should really buy a bigger unit than that because you are a fool if you dont. Many types of loads draw surge currents that might trip the breaker or blow the fuse of the lower power converter so to handle the surge you need a higher power unit in many cases.

    Good luck with it.
     
  6. Brendon Drew

    Thread Starter New Member

    Sep 19, 2016
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    Thabk you very much for your very indepth explination. This is the basis for a much bigger instalation (caravan that will be powered have alot of power and solar charging and the like) cheers for your help
     
  7. MrAl

    Well-Known Member

    Jun 17, 2014
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    Hello,

    Oh ok, well you are welcome.

    Maybe you can consider breaking up the circuits like they do in houses anyway. One circuit 600 watts, another circuit 600 watts, third circuit 600 watts, etc., so everybody gets power on their own circuit.
    That can be a big advantage if somebody overloads the system as then only their single circuit will go down and everybody else still has power.
     
  8. Brendon Drew

    Thread Starter New Member

    Sep 19, 2016
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    That is acctualy very good idea, i like it.
    How would you sudgest i enable something like bringing in a mains supply when parked. Like a change over switch?
     
  9. tcmtech

    Well-Known Member

    Nov 4, 2013
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    If you need a mains transfer switch then all you need is to run your power inverters through a relay that has the inverter on the NC contact and the line input on the NO contact with the actual van load on the common. Then wire the relays coil to the AC line input so that whenever it live the relay closes and automatically switch the power over.

    For one inverter and one load a single SPDT relay would work but for two or three inverter s DPDT or 3PDT relay would be needed.
     
  10. Brendon Drew

    Thread Starter New Member

    Sep 19, 2016
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    Perfect, cheers that is what i will do :)
     
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