four 6v batteries, 2 CCs, 12v and 24v loads simultaneously

Aeronb
Aeronb Registered Users Posts: 8 ✭✭
in Off Grid Solar & Battery Systems #1
We are looking into setting up a charging station at our R/C airplane club's flying field.  Some members have 12v chargers and others have 24v chargers.  Will it work?  If we had two CCs with each set to charge a pair of batteries, then have the batteries all series together for 24v.  I would put two sets of leads out from each pair of batteries so that we would have access to 12v from each.  I hope this would help even the discharge from each half of the battery bank.  I would never parallel these leads.

Will each of the CCs work independently on their respective battery bank and bring it to a full charge?  At some point, due to uneven usage, one half of the bank might be at say; 75% SOC, and the other half could end up at say; 90%.  Maybe then someone comes along and puts on a 24v load and brings them down another 5% each.  All along the CCs are doing their job to get the batteries back up to full charge.  At some point when loading is light one pair comes up to full and some time later the other one does too.

I can't find a reason why this shouldn't work.  But I have a feeling that I'm missing something.  Any comments and insights are greatly appreciated.

Regards,
Aeron
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Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    If you have a string of batteries totaling 24V, and  you pull power of some in the middle, you are unevenly discharging some of the batteries.  A 24V controller will NOT be able to sense this, and some of the batteries will fail prematurely.

    Solution,

    Best
     2 battery banks, 1 at 12V and other at 24V, with 2 chargers

    Next best
     Split the charging, using 2 ISOLATED chargers, each charging 12V of the bank.   You will find out quickly what chargers are NOT isolated, because there will be sparks and smoke

    Next best
    split the bank apart and charge one 12v section one day, move the charger to the other 12v section next day, and then reconnect to a 24V bank,   Lots of connecting and moving around


    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

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  • Aeronb
    Aeronb Registered Users Posts: 8 ✭✭
    #3
    mike95490 said:
    If you have a string of batteries totaling 24V, and  you pull power of some in the middle, you are unevenly discharging some of the batteries.  A 24V controller will NOT be able to sense this, and some of the batteries will fail prematurely.

    Solution,

    Best
     2 battery banks, 1 at 12V and other at 24V, with 2 chargers

    Next best
     Split the charging, using 2 ISOLATED chargers, each charging 12V of the bank.   You will find out quickly what chargers are NOT isolated, because there will be sparks and smoke

    Next best
    split the bank apart and charge one 12v section one day, move the charger to the other 12v section next day, and then reconnect to a 24V bank,   Lots of connecting and moving around


    Option number one hadn't even crossed my mind.  I guess that's why these forums are in such high demand.  The only down side to that one is the additional investment in a couple more batteries.  Option number two is the one I think I was trying to describe so it seems that the plan is at least viable.
    Thanks for your help.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #4
    There are charge controllers which charge 12 or 24 volt which have a 12 volt power port which you can tap 12volt out of. I'm not sure how well they work or what kind of loads they can supply.

    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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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #5
    Aeronb said:

    mike95490 said:
    If you have a string of batteries totaling 24V, and  you pull power of some in the middle, you are unevenly discharging some of the batteries.  A 24V controller will NOT be able to sense this, and some of the batteries will fail prematurely.

    Solution,

    Best
     2 battery banks, 1 at 12V and other at 24V, with 2 chargers

    Next best
     Split the charging, using 2 ISOLATED chargers, each charging 12V of the bank.   You will find out quickly what chargers are NOT isolated, because there will be sparks and smoke

    Next best
    split the bank apart and charge one 12v section one day, move the charger to the other 12v section next day, and then reconnect to a 24V bank,   Lots of connecting and moving around


    Option number one hadn't even crossed my mind.  I guess that's why these forums are in such high demand.  The only down side to that one is the additional investment in a couple more batteries.  Option number two is the one I think I was trying to describe so it seems that the plan is at least viable.
    Thanks for your help.
    Option number one, is the one which will be the least problematic, trying to tap 12V from a 24V bank will result in disappointment. What you spend up front will save you in the long run.
    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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