Mppt with generator input

Meyrick
Meyrick Registered Users Posts: 1 ✭
in Solar Beginners Corner #1
Hi all, off grid in the UK. So my 700w of panels going thru epsolar 30a mppt to 2x6v rolls battery bank(225ah x2) ain't holding enough charge to see us through the winter nights. Want to have a generator backup to charge batts. Is there a unit that will do it all in one or do I have to split the charging facilities and simply put a decent battery charger on the generator. Was wondering if there was a dual unit, that'll do both charging inputs. Ps why might my rolls that are only a year old go from 12.8 to 11.8 in one eve with just a few led lights connected . Surely not enough draw to do that ? Thanks in advance 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    There are inverter chargers available however the choices in 12V are limited, most being modified sine wave, lower cost a few sine wave higher cost https://www.solar-electric.com/exxp12vol11w.html these will allow a generator ac output to be used for charging, some may allow passthrough to support loads whilst charging.

    With reference to loads, it would be difficult to speculate without actual figures, load current, inverter self consumption and hours of operation. Some inverters can conume a surprising amount of energy even without load, so left on all night. Using 12VDC lightning is way more efficient if that's all the loads are, lots of guessing at this point.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • petertearai
    petertearai Solar Expert Posts: 471 ✭✭✭✭
    #3
    all depends on what your loads are . What is the SG your batterys are at  at the end of day . 700 watts seems to be a small system  for off grid .
    2225 wattts pv . Outback 2kw  fxr pure sine inverter . fm80 charge controller . Mate 3. victron battery monitor . 24 volts  in 2 volt Shoto lead carbon extreme batterys. off grid  holiday home 
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #4
    Unfortunately, the most likely explanation for a bank going from 12.8v (apparently full, if a "resting" voltage) to 11.8v (more or less fully discharged) with little load, is a badly sulfated or otherwise damaged battery.

    Checking SG at full charge would be useful info.
    Off-grid.  
    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
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #5
    Consider having your batteries tested.

    I am available for custom hardware/firmware development

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #6
    What is happening when measuring 12.8 volts?

    Has the sun set, stopped charging, battery rested for a few hours?

    It was the 12.8 volts during the middle of a sunny day? (Ideally, you want around 14.8 volts held for several hours during charging, and floating at 13.6 volts or so after charging is complete and before the sun set.

    It sounds like the batteries were not fully charged, or over discharged, and the batteries sulfated (batteries best end of life).

    Using a hydrometer to measure specific gravity (flooded cell lead acid) is the gold standard.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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