AC Coupling

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bobbypat50
bobbypat50 Registered Users Posts: 3 ✭
in Advanced Solar Electric Technical Forum #1

I have a Xantrex SW 5548 that I plan on AC coupling to an Outback Radian GS8048A-01. The Xantrex is fed by my solar array No. 1 (2kw, 48v), through an Epever Tracer charge controller (80A, 48v).

The Outback will be fed by my other 2 solar arrays No.s 2 and 3 (each 3kw, 48v), through a pair of Outback MX 60's (60A and 48v each), and monitored by a Mate 3.

I have 2 independent LiFePO4 battery banks from 2 different manufacturers, both of which are 48v w/BMS, wired independently in parallel, with similar charging specs from each of the manufacturers.

One is a 3-battery bank, (30kwh), which I intend to connect directly with the Outback inverter, while the other is a 2-battery bank (10kwh), which I intend to connect directly to the Xantrex.

I've been led to believe that one should not parallel-connect batteries from 2 different manufacturers, hence the separate wiring scheme for each battery bank to each inverter, with no interaction between the battery banks.

Will this setup have any negative impact on the Outback's AC coupling operation, by having 2 separate battery banks?

If so, should I ignore the warnings, and wire both banks together in parallel to the Outback, such that the Outback sees only one huge battery bank that is fed by 3 solar arrays with a separate charge controller on each array to the common battery bank?


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  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #2
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    Details matter here... I think you are going to need to talk/hire an engineer familiar with the equipment you plan on using...

    This sounds like a large system and there are a lot of things that could go wrong if not done correctly...

    I would be tempted to pick one vendor for your hardware and network it all together... That way, you are not left trying to figure out the Xantrex/Schneider/Outback issues. Also with Li Ion and BMS--Ideally you would want a BMS that could talk with/network with your inverters and charge controllers. Not a trivial exercise to try and take "random" hardware and make it work together in a large system.

    I guess you are in the Monterey Bay California area?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bobbypat50
    bobbypat50 Registered Users Posts: 3 ✭
    #3
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    Good morning Bill.

    Yes I am located in Prunedale... on the Monterey Peninsula. 

    My battery BMS has dual RS485 to communicate with the other components.

    I appreciate your advice on picking a vendor, but that's no easy task to find someone that I trust who is  well versed with both the old Xantrex and newer Outback. Therefore I've been left to sort it out myself, with  online support from wonderful forums such as this.

    Both inverters have GTI and are set up to provide DC coupling, but I don't believe the older Xantrex meets the rigid new updated Calif requirements ... whereas the Outback does... hence the AC coupled idea. With the Xantrex piggybacked off the Outback, I should be able to get approval of the system without hassels from the State.

    As I reflect a bit, I believe my approach of keeping the battery banks separate would be the wiser choice here. The way I see it now, they should act as 2 separate DC systems that way, connecting and interacting as 1 unit only on the AC side. 

    Bob




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  • bobbypat50
    bobbypat50 Registered Users Posts: 3 ✭
    #4
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    Update:

    In different forum, a user pointed out the error in my thinking of AC Coupling.
    The Xantrex is a 120v single phase inverter, while the Outback is a 240v split phase, so it's a no-go for AC Coupling here.

    So... I guess the Xantrex goes up on Ebay, and I find either a compatible inverter with 240v split-phase for AC Coupling, or
    I find a CA approved inverter for DC Coupling.


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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    edited July 2021 #5
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    Any grid tie interactive inverter with AC coupling must be master for AC voltage/phase.  You cannot parallel output connect two AC coupling capable inverters unless they have ability to be slaved.  Most newer inverters have a separate syncronizing control wiring.  Inverter generators like Honda and others can be paralleled because the first started generator becomes the master for the other generator.  You cannot parallel connect them when they are both running before you attempt to making the parallel connection.  They would both be running with their asynchronous phasing.

    The Xantrex SW 5548 would be the master for voltage/phasing to the Outback since the Xantrex does not have AC coupling control.

    Even if you had two series connected SW5548's for 240v, my guess is any momentary current push by the Outback inverter, which is normal for grid interactive inverters, will cause the Xantrex SW 5548 to throw an error and shut down with "input AC connected to ACout" error.

    Best you could do is run Outback as AC input to Xantrex and use AC current input current limit on Xantrex with Xantrex supplimenting AC load output.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,746 ✭✭✭✭✭✭
    edited July 2021 #6
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    Especially in California! The old SW and old grey box XW are not going to fly. It is seriously hampered in design for PG&E if you need a permit for insurance.

    It was replaced by XW pro which is super fast for AC coupling and is perfect for lithium batteries. It will charge them and frequency shift when they are full based on state of charge. Xwp is also compliant with Rule 21 for California

    .https://solar.schneider-electric.com/product/xw-pro-na-solar-hybrid-inverter/
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #7
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    The old SW inverter use three series secondary winding connected transformers (Papa 90v, momma 45v, and baby 15v size).  This gives up to 27 discrete output AC waveform steps that approximates sinewave which does not meet harmonic content regulations for grid push.  

    They made a 'band-aid' grid tie adaptor box that is primarily just a big filter choke to remove choppy steps in synthesized sinewave.
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