Rv alternator charging battery bank issues

Not a solar question but someone still may be able to help me. I have a class c motorhome and recently had a new outback VFX 2812 inverter charger installed with a 3 ,group 24 agm battery bank. The chassis engine electrical system was completely gone over as well ,replacing the alternator with a new 135 amp model. The plan was to have the new alternator charge the batteries when driving or even while parked for awhile to bring the batteries up to snuff. Does not seem to be working correctly. Seems to be charging less then what I expected. From the research I have done folks seem to recommend a Zantrex alternator regulator. Will this do the trick? Do I turn the inverter off while driving? The concern would be that the altenator would charge the batteries and the inverter charger tries to charge them at the same time. Am I missing something? I have the guys that put this in for me ordering the new Flexnet DC from outback . It is a complete DC monitoring system and came highly touted. The plan down the road is to put a generator in the bay or several solar panels but I was hoping to get by with the altenator charging system for on the road when not plugged in to shore power. I am getting alot of money invested and do not want to throw good money after bad but shouldn't this work? My first post so if this is the wrong forum maybe someone could redirect me.
Thanks in advance
Dan Berg


  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Rv alternator charging battery bank issues


    Automotive alternators and their stock regulators are not particularly good at charging deep-cycle batteries. The absorb stage voltage for a 12 V AGM battery bank is ~14.25 V measured at the battery terminals. I’d be surprised if your vehicle's charging system can do that when the alternator is hot. The 135 A alternator won’t help if the charging voltage isn’t high enough.

    Three Group 24 batteries is not a particularly large battery bank for an RV equipped with a huge inverter. Each battery is rated at ~80 Ah. Limiting maximum discharge to 50% state-of-charge (SOC), you have 120 Ah available for powering loads.

    A 2812 (2,800 W, 12 VDC to 120 VAC) inverter/charger is pretty big for a class C motorhome. If nothing else, its idle load (~20 W) will be a continuous drain on the house batteries. Doing nothing but idling, it’ll consume ~40 Ah/day, or ~1/3 of your battery bank’s usable capacity.

    The 2812 operates as either an inverter (12 VDC to 120 VAC) or as a charger (120 VAC to “12 VDC”). It’ll only operate as a charger if it’s plugged into shore power or a generator.

    So, what’s the solution? You might need a three-stage regulator from Xantrex or Balmar. But, you’ll need to see what the higher voltages will do to your automotive battery. Turning off the inverter/charger when you aren’t powering AC loads will save you a huge amount of energy. On/Off options for OutBack inverter/chargers include a hardwire switch or using a Mate controller.

    An alternative to the 3-stage regulator might be some PV modules and a multi-stage controller. Set up correctly, such a system can help provide energy while boondocking, recharge the batteries when your cruzin’ down the road, and also help maintain the batteries when the RV is parked.

    Jim / crewzer
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: Rv alternator charging battery bank issues

    I'm not famailar with the Zantrex, but the regulators/alternators at http://www.balmar.net/ are designed to do what you want. Deep cycle batterys have a different charge voltage than engine starter batteries.
    Something like a high voltage (15V) regulator and their Duocharge, or just get an additional high amp (I understand you just paid for one that does not do the job) solely for the living battery (not starter) http://www.balmar.net/page20-Duocharge.html
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • System2System2 Posts: 6,290 admin
    Re: Rv alternator charging battery bank issues

    Thanks Jim
    I was probably oversold on the Outback but its in and works good so I will make the best of it. I will see what the electric firm that is doing the work thinks about all this and will let you know the outcome.
  • System2System2 Posts: 6,290 admin
    Re: Rv alternator charging battery bank issues

    Don't be surprised if the "electric firm" does not understand what Jim is talking about. It's a field within a field, with it's own expertise.
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