SDCacti: 8x Duracell AGM battery bank and some panel--Help

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in Solar Beginners Corner #1
This discussion was created from comments split from: Battery charging.
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  • SDCacti
    SDCacti Registered Users Posts: 9 ✭✭
    #2
    I got an issue I have not been able to figure out yet, my system is an array of 2x 270 24v panels, 2 & 4 100wt 12vt panels in series connected to a combiner box- I have a outback flex 60amp controller, 3000 watt aims pure sine inverter, and a bank of 11x 80ah 12v batteries in series parallel. live in southern california and its been little overcast lately but for some reason i am stuck right around 23.5-23.8v from the batteries during the day when 40 watts is all that is being powered during that time. this is a recent occurance. anyone have any ideas?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    edited June 2019 #3
    What are the Vmp and Imp of your different panels?
    They may not be a good candidate for mixing into a single array for your Outback MPPT charge controller ...
    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • SDCacti
    SDCacti Registered Users Posts: 9 ✭✭
    edited June 2019 #4
    ahhh..  shoot. two are 17.9 and 2 are 30.something. was trying to make some use of the old 12 volt panels but perhaps better to bite the bullet and just get 2 more 270wt 24v panels so its consistent.  Well anyone in san diego that wants some 12 v panels they'll be flying off the roof tommorrow!
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,113 ✭✭✭✭✭
    #5
    The 270 watt panels aren't 24 volt panels. You will need to wire your panels 2s2p.

    11 batteries in series/parallel, can you describe how they're configured? 

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • SDCacti
    SDCacti Registered Users Posts: 9 ✭✭
    #6
    per the panels.. unless they are improperly labelled they say 24v on them.  vmp is 31.4, voc is 38.6 they are 60x40". how the batteries are wired is correct for even charge and i just woke up so dont wanna draw it out but for sake of tech debate coming from  + term block on din rail using 4ga  cable going to battery 1 (pos) which is then daisied on down 5 batteries. + to + the  neg cable is on the last battery from term block that row is - to -  but on top row those neg are tied to the pos on bottom row so theres a poor mental schematic of the 10 batteries for ya
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  • SDCacti
    SDCacti Registered Users Posts: 9 ✭✭
    edited June 2019 #7
    and if anyone knows ballpark absorb and float setpoints or how to figure those out would be much appreciated they are 80ah duracell sealed deep cycle batteries
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #8
    "24 volt" is a loaded term for solar panels... Technically, those panels run Vmp-hot ~ 24 VDC.

    However, you need >29.0 volts to charge a 24 volt battery bank, add a few volts for wiring and controller voltage drop (plus panels run Vmp-hot at closer to 80% of Vmp-std-test-conditions...

    So, for a "24 volt battery bank" running a PWM charge controller, you need Vmp~35-40 VDC "nameplate" rating.

    And many "Grid Tied" panels are 60 cell or Vmp~30 volt rated.

    For use with an MPPT type charge controller, you need the Vmp-array to be, at least 1.3x the charging battery bus voltage and really closer to 2x battery bus voltage for ideal operation (the higher Vmp-array is, the MPPT controller becomes slightly less efficient--But we don't usually worry much about that "extra" couple percent loss). 2x Vbatt minimum is a good place to start.

    For AGM Batteries 14.4 volt volts Absorb setpoint is typical max (28.8 volts for 24 volt bank). For GEL, 14.2 volts is typical maximum.

    Absorb timing, for shallow discharge you can go with 2 hours... For deep cycle start with ~6 hours. Another way is to monitor the charging current... When it falls below ~1% of the Battery 20 Hour rating, it is full enough... 80 Amps * 0.01 rate of charge = 0.8 amps to terminate charging cycle/fall to float.

    13.5 volts for Float (AGM/Sealed) is probably a good start if you cannot find Duracell's information.

    Here is the Trojan manual:

    https://www.trojanbattery.com/tech-support/battery-maintenance/

    -Bill "I am not a battery engineer" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #9
    Kind of strange... I am bumping this discussion so that is "new again".

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