Setting SoC cut-off for inverter

Have a Victron Multiplus 3000 connected to 2 Lithium Ion batteries (Tesla Model S modules) and I want to avoid always charging back up to 100% when I am not regularly using my RV.  I understand that keeping the batteries at a lower SoC (like 50%) is better for battery life and then only charging up to 100% shortly before a trip.  Is there a way I can set the Inverter to quit charging the batteries at 50% sometimes and then change back to fully charging them when needed?  (PS- If you can't tell, I am new to all this).


  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    Since it's a known point in time, when you would be parking and not using, you could just do it manually. 
    Install a manual disconnect, so you know the battery bank won't be drawn down.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former, 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • clarksandquist
    clarksandquist Registered Users Posts: 2
    Thanks for the response.  I do have a manual disconnect and can use that, however, I am considering times like this winter, where I am not winterizing the RV because I want to use it occasionally, but the temperatures are low enough to require that I run some low level of heating (~40 degrees) to keep the pipes from freezing.  This will create periodic demands on the battery/inverter, but not enough to keep the batteries from running up to and staying at 100% if connected to shore power.  If I am not connected to shore power, the batteries will totally run down after about 24 hours.  Right now I am daily connecting and disconnecting from shore power to manage it.  Would prefer to leave it connected to Shore power and have the charging stop when the battery reaches 60-70% SoC to keep from overcharging without my daily intervention.  I understand that in Tesla's you can set the level of charge to avoid having it run up to 100% when you don't have a need for it to extend the battery life.  Was hoping for something similar.   Any ideas?
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    edited December 2021 #4
    Model S cells range from 3.3v to 4.2v with 3.8-3.9v mid range voltage.

    I assume you are running  22.8V nominal voltage modules made of total cell count of 444 Panasonic NCR18650B cells running in a configuration of parallel groups of 74 cells, with 6 groups in series, either one module for 24v inverter or two modules in series for 48v inverter.

    To charge a bit over 50% SOC you would charge with absorb voltage setting of 23.4 vdc per module. This is about 3.9 v per cell.

    Greatest stress on these batteries is electrolyte degradation which is greater at higher voltages.  Cells must not be allowed to go over 4.3v per cell as this is the point where accelerated electrolyte degradation gets really damaging.