multiple small pwm charge controllers on 48v bank

Estragon
Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
in Off Grid Solar & Battery Systems #1
I'm thinking of putting multiple pwm charge controllers on a 350ah 48v bank for winter float charging, eg 2x24v MN brat controllers with either a couple of 12v panels in series, or maybe just a big panel.  Can anyone see any problem with this?
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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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    edited March 2017 #2
    Estragon said:
    ..., eg 2x24v MN brat controllers with either a couple of 12v panels in series, or maybe just a big panel.  Can anyone see any problem with this?
    Not enough voltage, you would need at least 4 - 12 volt nominal panels in series to reach 48 volts, with larger panels, you would need 2 - 34+ vmp panels or 3 - 22-32 volt panels, check to see if the controller can handle the extra voltage.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
    I was thinking of maybe 2x12v panels in series for~35v into 2x24v pwm controllers, each taking 1/2 of the 48v bank. There would be little, if any, load on the bank - mainly to keep a float on.
    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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  • dennis461
    dennis461 Registered Users Posts: 109 ✭✭✭
    edited March 2017 #4
    You will need to check how the negative wires are connected internally in the PWM.
    If you have only two wires coming from your solar array, then you will have a common negative on both PWM's.
    Now, the first PWM will connect e.g solar common (-) terminal to (-) lower 24VDC battery. (+)  solar to (+) of 24VDC battery
     then the second PWM will connect e.g solar common (-) terminal to 'upper (-) 24VDC battery (which gets you 48). (+)  solar to (+) of 24VDC battery.

    In my mind, this basically shorts out the lower 24VDC battery and makes smoke.


    -(-)-------24vdc---(+)—(-)-------24vdc-------(+)------



    Camden County, NJ, USA
    19 SW285 panels
    SE5000 inverter
    grid tied
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited March 2017 #5
    Estragon said:

    I'm thinking of putting multiple pwm charge controllers on a 350ah 48v bank for winter float charging, eg 2x24v MN brat controllers with either a couple of 12v panels in series, or maybe just a big panel.  Can anyone see any problem with this?
    Why not use a Morningstar TS60,45 or 30, they can charge 48v at about the same price or less, as 2 MN Brat's, seems a simpler solution.
    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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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #6
    @dennis461

    I think I see what you're getting at. Sort of.
    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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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
    @mcgivor

    The thought was to avoid shipping a couple of big panels or more small panels. It won't take a lot of current to float so the extra is a bit of a waste. I might go that route though.
    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
    · Share on Twitter

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