Midnight classic vs Battery Monitor %

DclineDcline Registered Users Posts: 2 ✭
in Advanced Solar Electric Technical Forum #1
Can someone tell me what these 2 are showing such a difference in the % but yet the volts are very close. 
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  • PhotowhitPhotowhit Solar Expert Posts: 5,550 ✭✭✭✭✭
    #2
    If they are both using a shunt based meter, the info is only as good as what has been told to the equipment.

    Volts is a poor way of estimating battery capacity in a active system.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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  • mike95490mike95490 Solar Expert Posts: 9,251 ✭✭✭✭✭
    #3
    The one with the properly wired shunt and configuration is right..
    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 ,

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  • BB.BB. Super Moderators, Administrators Posts: 31,470 admin
    #4
    There is also the possiblity that the Battery Monitors are both shunt based (measuring current * time * direction) properly... But they tend to drift over charge/discharge cycles. Many (some/most/all?) BMS will reset to 100% State of Charge with absorb voltage is held for X hours... If it has been a while since the absorb voltage has been held for a few hours, BMS drift is possible. 

    Also, many BMS will have various settings (absorb voltage, absorb time to resync to 100%, battery AH capacity, battery "efficiency", etc.)... Another source of possible "drift" between units.

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