2 inverters in one system

tonygcan
tonygcan Solar Expert Posts: 91 ✭✭✭✭
in General Solar Power Topics #1
My friend is thinking of installing a 3 phase inverter in addition to his single phase inverter to his existing battery bank of 1200 Ah.

Is this possible? Can one actually run a single phase and a three phase together?

He wants to connect 2 refrigerators that have 3 phase motors to his RE system.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: 2 inverters in one system

    As far as the DC is concerned, you can run any number of inverters from the same battery bank as long as there is sufficient capacity to handle the loads. Wiring should be separate to each and fused accordingly.

    On the AC side there is of course no connection between the inverters.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: 2 inverters in one system

    What does he need to do with the 3 phase inverter?

    If he is driving something like a mill or a lathe with a 3 phase motor, many times it is possible to "cheat" with single phase power...

    One method is to get a large three phase motor (ideally "star" or "Y" wound) as a rotary converter. Power two of the legs from your single phase 240 VAC, and connect all three legs to the three phase equipment. If it has 240 VAC controls, I make sure they are wired to the two "true" 240 VAC legs.

    You can use a three phase starter box (motor start capacitor with voltage sensing relay) or even wrap a cord around the idler motor and give a pull (like starting a gasoline engine)--Then turn on the 240 VAC single phase... Motor will turn up to speed and give a good enough 3 phase on the third leg that everything should run fine.

    The other is to use the three phase starter box directly on the lathe.

    There are lots of websites out there to tell you how to do it. It may look a little confusing but virtually all of the different diagrams are pretty much the same couple of circuits.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tonygcan
    tonygcan Solar Expert Posts: 91 ✭✭✭✭
    #4
    Re: 2 inverters in one system

    Thank you Marc and Bill,
    Much appreciated info. He has 2 industrial Chiller / freezer units that use 3 phase motors. He has excess capacity on his batteries right now and he was thinking of connecting a 3 phase inverter to run the industrial 3 phase chillers.
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  • tonygcan
    tonygcan Solar Expert Posts: 91 ✭✭✭✭
    #5
    Re: 2 inverters in one system

    Just posting message from my friend.

    "Dear Tony & Bill,

    Thanks for your help. I am aware of that 1 phase can be made 3 phase using motors.

    I will power: 3 small 5/8 hp pressure balancing water pumps for my baths, 2 - 1 1/2 hp compressors for my chiller and freezer.

    Maybe its wiser to run these with a separate inverter. Because the additional batteries i will install can also power a lot of small additional 1 & 3 phase loads immediately and in the future.

    Lastly, i dont know anyone near who can make and MAINTAIN this conversion.

    Joel"
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: 2 inverters in one system

    My fear is that three phase makes everything 3x as expensive... And the smaller 3 phase off-grid inverters that I have seen are in the 4-6kW per leg class... pretty much around $10,000 USD just for inverters.

    Not a small installation.

    If your friend has grid power already... Perhaps looking at a XW type inverter with load shaving... Basically, attach the inverter between the utility and the single phase AC loads. Program the inverter to supply the AC loads with any and all available solar/battery energy (i.e., keep the batteries in float, but anything > float is available to help share the AC grid load).

    This bypasses the issue of pure Grid Tied and backfeeding the utility line (which many utilities don't like because it looses them revenue and possible safety/grid concerns).

    Unless the Battery system + solar array is huge--Just install one inverter (single phase) and power the rest of the AC single phase loads through the XW and load shaving. Let the coolers run off of line power/generator backup (if appropriate).

    Perhaps others here know of smaller 3 phase-able off-grid inverters that don't cost an arm and a leg and a first born child.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • tonygcan
    tonygcan Solar Expert Posts: 91 ✭✭✭✭
    #7
    Re: 2 inverters in one system

    Thanks for that Bill. Definitely a better alternative. And yes, our power utility is not ready to grid tie their system just yet.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #8
    Re: 2 inverters in one system

    He can also use a Variable Frequency Drive to turn 1 phase into 3 phase. A VFD is actually a mini 3-phase inverter itself specifically designed for 3 phase motors. They can help soft-start a motor so that it doesn't go from 0 to 60Hz instantly, but rather ramps up slowly over a few seconds - this is gentler on the motor and avoids startup surges.

    The speed of a 3 phase motor is directly proportional to the line frequency, with a VFD you can choose to run the motor slightly faster or slightly slower. I've done this with my pump, which was designed as a 50hz model, but have run it at 54Hz to increase the flow rate.

    Definitely a lot cheaper than buying 3 off-grid inverters.
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  • tonygcan
    tonygcan Solar Expert Posts: 91 ✭✭✭✭
    #9
    Re: 2 inverters in one system

    Hi Bill, from Joel -

    Thanks Bill & Tony,

    Thanks for the good words. Yes, you are soo right.

    But there may be a solution to be found in cheaper, 3 phase inverters
    made in india. If not, i may certainly take your advice.

    I am on 3 phase because we have a small production of soaps etc. This
    has saved me a lot on power and maintenance of single phase machines
    that have all been replaced with 3 phase machines that have yet to
    conk out after more than 4 years. We are also expanding capacity and 3
    phase is certainly the way to go. But my remaining residential loads
    are in 3 phase.

    As i increase my learning on solar and wind energy, i realize that 3
    phase RE is rare, therefore costs can be prohibitive.

    I will advise you periodically through Tony on whatever happens.

    Thanks again,

    Joel
    www.ilogmaria.com
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  • blackswan555
    blackswan555 Solar Expert Posts: 246 ✭✭
    #10
    Re: 2 inverters in one system

    I am with Stephen on VFD`S, Great bit of kit for 3 phase motor`s :D
    Tim
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #11
    Re: 2 inverters in one system

    Yep I have a Boyar Schultz surface grinder getting a VFD this summer. The easy way to run a 3 phase motor.
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  • tonygcan
    tonygcan Solar Expert Posts: 91 ✭✭✭✭
    #12
    Re: 2 inverters in one system

    Thanks Stephen,

    I've not studied the VFD option but will do research on it now and suggest it to Joel.
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