Balancing 12x6V batts in a 24V system

dapago
dapago Registered Users Posts: 62 ✭✭
in Off Grid Solar & Battery Systems #1
hello to the community,

I have a battery bank composed of 12x6V batts for a 24V solar system wired 4S3P.
I am a bit worried not to be able to balance properly the second serie of 4 batts (in the middle).

I have found 2 diargrams that allow to perfectly balance a serie of 4 + batts but do not know how to apply those diagrams to batts wired in parallel. Someone could help?

i have attached a picture to show the 2 options proposed. For the full article relating to those wiring, please refer to http://www.smartgauge.co.uk/batt_con.html
Off-grid. Midnight Classic 200. 2,480W array. Magnum Inverter MS4448PAE. 225Ah*8 @48V Trojan T105RE Smart Carbon. MN bkrs box.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    The diagrams show 4 batteries in parallel, method 4 in the smartgauge link would probably be the best with 3 batteries, the only drawback is the number of cables and lugs needed, method 2 will still favor the outer batteries in a 3 parallel setup, method 3 is not possible with an odd number of batteries. Another method is to use bus bar to connect all the positives together, and another to connect all  negatives together, attaching load and charge points diagonally opposite of the center battery, midway between center and outer batteries , by battery I'm referring to each string of 4×6V, this method makes for a clean instalation, the bus bars must be sized correctly, and bigger is better.   
    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.  
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  • dapago
    dapago Registered Users Posts: 62 ✭✭
    edited October 2017 #3
    mcgivor said:
    The diagrams show 4 batteries in parallel, method 4 in the smartgauge link would probably be the best with 3 batteries, the only drawback is the number of cables and lugs needed, method 2 will still favor the outer batteries in a 3 parallel setup, method 3 is not possible with an odd number of batteries. Another method is to use bus bar to connect all the positives together, and another to connect all  negatives together, attaching load and charge points diagonally opposite of the center battery, midway between center and outer batteries , by battery I'm referring to each string of 4×6V, this method makes for a clean instalation, the bus bars must be sized correctly, and bigger is better.   
    Thanks for your answer. I know it might be asking a lot but could you post the diagram you suggest? Or refer to a diagram on the web?
    I like the bus bar you are referring to. Where can I find them?
    Off-grid. Midnight Classic 200. 2,480W array. Magnum Inverter MS4448PAE. 225Ah*8 @48V Trojan T105RE Smart Carbon. MN bkrs box.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,105 ✭✭✭✭✭
    #4
    Method three , without actually saying it is how you would incorporate buss bars.  Make up your cables figuring the required length of the longest one, then make all cables the same length. I made my buss bars out of foot long lengths of 1 1/2" x 1/4" copper stock, Be sure to use either stainless steel or bronze bolts for your connections.

    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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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #5
    My understanding is with more than 2 parallel strings, a fuse or breaker is required on each. I assume with a bussbar, it would go between the positive bussbar and the battery post on each string?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
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  • dapago
    dapago Registered Users Posts: 62 ✭✭
    #6
    Estragon said:
    My understanding is with more than 2 parallel strings, a fuse or breaker is required on each. I assume with a bussbar, it would go between the positive bussbar and the battery post on each string?
    I am a bit confused. If someone could make me a quick diagram including those strings breakers that would be very very helpful. Unfortunately where I live I have to manage the installation myself and I am not n expert at all. 
    Off-grid. Midnight Classic 200. 2,480W array. Magnum Inverter MS4448PAE. 225Ah*8 @48V Trojan T105RE Smart Carbon. MN bkrs box.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
    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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  • dapago
    dapago Registered Users Posts: 62 ✭✭
    #8
    Estragon said:
    +++++++. Thanks a lot. I will now need to study that diagram and try to understand it hehehe. 
    Off-grid. Midnight Classic 200. 2,480W array. Magnum Inverter MS4448PAE. 225Ah*8 @48V Trojan T105RE Smart Carbon. MN bkrs box.
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