How to Utilize 12V & 48V Battery Systems

OTG_Fan Registered Users Posts: 1
I'm planning to implement about a 12KW off grid system in November/December on an acre of land we are buying which will have a house moved in. We want to utilize our existing diesel GenSet (7.5KVA diesel) and 1000 AH @12V of battery storage in our RV.

We plan about 36 x 350W of PV panels producing approx 12.6KW, and I am reading about MPPT charge controllers.

Our setup is somewhat unique: We have an RV which we use constantly, and it already has five strings of 12v deep-cycle, golf cart batteries (6v+6v) wired together. We cannot change that (at all), and we are happy with the system which provides 1000 AH of storage. We discharge batteries to 50% overnight and use a 7.5KW diesel Genset in the RV for bulk charge, and a second truck alternator (270 Amps) to charge the ten batteries (5 strings) as we drive along, and run an A/C or Heatpump off the RV's inverter. We control temp, but that's a side story.

The essence of my question is whether anyone has experience (or an opinion) on utilizing two different DC Voltage banks. I am thinking we could use an MPPT controller @ 12V for the RV batteries, and another MPPT controller (or two) for two planned strings of 48V batteries from the same manufacturer (each string 6V x 8 batteries, twice over)

It occurred to me to ask whether we could use the same brand of Inverter to "stack" the output to achieve 12KW. If the inverter brand (I have no prefs) could support different input voltages, could I use one with 12VDC in, and another (or two), with 48V in?All I need is a 120V synchronized, split system output at 120V to feed L1 & L2 at the house panel.

Is there a manufacturer offering stacked inverters that can support different input voltages on each inverter? In an ideal world, I'd like to have a system which allows each inverter to communicate with its MPPT controller and combine the outputs.

Then of course, the decision around when to start the generator, and which DC string it would monitor.

Lastly, when we travel, we would unplug the RV and the "other/s" inverter would remain connected to it's charge controller and battery string/s. 

If you have read this far: thanks and looking forward to reading and learning...



  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    all inverters I've heard of, work only at one input voltage.

    >  All I need is a 120V synchronized, split system output at 120V to feed L1 & L2 at the house panel.
    That's either going to require an expensive +4kw inverter, or a cheap inverter and an expensive autotransformer

    Powerfab top of pole PV mount | 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

    gen: ,

  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    There are inverter families (eg Outback FX series) which would let you use very similar inverters in the RV and the house.  The 48v house inverter could be stacked in series/parallel for higher output and/or 120/240v.  AFAIK, there's no inverter with multiple site selectable input voltages.  Lots of charge controllers can be set for different output voltages though.

    They will be two separate systems, so it's a question of whether the advantages of using the same family (similar installation, programming, menus, etc.) outweigh possible downsides (eg. a 12v version in the same family may lack features you might find in a different family). 

    For the RV, you'll likely want a mobile specific version (eg. switched neutral on shore power x-fer switch)
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter