batteries 12V parallel charging 24V series load possible?

t0nito
t0nito Registered Users Posts: 5 ✭✭
in Off Grid Solar & Battery Systems #1
Hi, I want to set up a small off-grid setup, but I'd like to work with what I have as I'm in a tight budget, I have a 240W 60 cell (20V nominal) panel, a mppt controller compatible with either 12 or 24V batteries, 2 12V batteries and a 660W 24V ups I had laying around to use as an inverter. The panel itself won't be able to charge the 24V battery so I was thinking of connecting both batteries in parallel to the controller to charge them at 12V, and connecting the inverter to both batteries in series to make 24V is this possible? 
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Yes, it will work, but is not ideal.

    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • t0nito
    t0nito Registered Users Posts: 5 ✭✭
    #3
    Ok, thanks! Out of curiosity, why isn't it ideal? Wouldn't both batteries be charged evenly and discharged evenly in this setup?
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  • bsolar
    bsolar Solar Expert Posts: 103 ✭✭✭
    #4
    you'd have to rewire the bats and wouldnt be able to take advantage of panel output during the day .. i know not much about factory panels but have you actually read it out with a meter in the sun? sure it wont put out like 30ish?
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  • Horsefly
    Horsefly Registered Users Posts: 476 ✭✭✭✭
    #5
    Every charge / discharge cycle you will rewire the batteries. Sounds really inefficient to me. If you hope to accomplish this with switches rather than rewiring, you'd better have some pretty clear instructions on which order to do things, else really bad things will happen.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #6
    bsolar said:
    you'd have to rewire the bats and wouldnt be able to take advantage of panel output during the day .. i know not much about factory panels but have you actually read it out with a meter in the sun? sure it wont put out like 30ish?
    If you were to attempt charging each battery individually, imbalance of capacity would result leading to premature failure of both batteries. AS @bsolar said the panel, 260W 60 cell, should be able to produce ~30 volts, but this is still not sufficient to charge a 24V nominal battery, 2  of the same panels in series would be ideal with an MPPT controller.
    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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  • nickdearing88
    nickdearing88 Registered Users Posts: 100 ✭✭✭
    #7
    Horsefly said:
    Every charge / discharge cycle you will rewire the batteries. Sounds really inefficient to me. If you hope to accomplish this with switches rather than rewiring, you'd better have some pretty clear instructions on which order to do things, else really bad things will happen.
    That will get old VERY quickly.
    Current system: 8-100w Renogy panels mono/poly, 2 strings of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
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  • t0nito
    t0nito Registered Users Posts: 5 ✭✭
    #8
    Ok, got it! Thanks for your replies. I guess I'll just keep both batteries in parallel and purchase a 12V inverter.
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  • mvas
    mvas Registered Users Posts: 395 ✭✭✭
    edited June 2017 #9
    t0nito said:
    Ok, got it! Thanks for your replies. I guess I'll just keep both batteries in parallel and purchase a 12V inverter.
    Here is a device that will charge a 24 Volt Battery Bank using a 12 Volt PV Panel.

    CV 12/24-12PV ...
    http://www.solarconverters.com/products/charge-controllers/cv-boost-charger/

    GenSun
    hhttps://genasun.com/all-products/solar-charge-controllers/for-lead/gvb-8a-pb-wp-solar-golf-cart-boost/

    Contact the vendor to verify which model can handle your Voc, Vmp, Amps, etc.
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