Best way to wire 3, 12v 175W Solar panels to 60A charge controller and 4, 12v deep-cycle batteries?

HSTDave
HSTDave Registered Users Posts: 1 ✭
in Solar Beginners Corner #1
Hi,

I am converting my boat to all electric and was wondering what is the best way to wire three 12v, 175W solar panels to a 60A MPPT charge controller? I have a battery bank consisting of four 12v deep-cycle batteries I planned to wire in series to get 48v. I have the panels and controller bought but have not bought the batteries yet. This bank will only be used for the motor which should consume about 30-50A a day. I am really new to wiring and solar so if there is anything I missed or messed up, drinks on me. Appreciate any and all suggestions

Thanks,
Dave
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    edited April 2020 #2
    My guess is the 3 x 12v nominal panels wired in series may not be high enough voltage to properly charge a 48v bank.  The bank will likely want an absorb charging voltage of ~58v.  Assuming panel Vmp of ~18v x 3 = 54v.  A 48v bank with mppt controller generally wants pv string Vmp of mid-60s or more, so you may need to add a panel?

    Depending on location may also want the extra panel to get you into your 30-50ah load range.

    Approximate location and panel specs would help.
    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,623 admin
    #3
    Do you want a 48 VDC bus on your boat? Most boat electronics are 12 or 24 VDC (at least the smaller stuff).

    What are your expected power requirements (for your loads), what is your planned bank AH @ VDC size, location, panel angles, sailing or power (i.e., shading from sails/lines), orientation during anchorage, etc...

    Solar Panels do not generate useful power if there is any shading (including just the shadow of a line across a panel). If you are going to put 4x panels in series (for Vmp-array ~72 volts or greater), they need to be mounted in an area without shade, and have good angle to the sun (big difference between a sailboat and a pontoon boat installation).

    Generally, for smaller systems (typically 1,200 to 1,800 Watts max for a 12 volt system), work well... A 48 volt system is usually for larger system power requirements (say ~3-4 kWatt loads or larger).

    And you need to discuss not only AH but voltage too... 
    • 40 Amps * 12 volts = 480 Watts
    • 40 Amps * 24 volts = 960 Watts
    • 40 Amps * 48 volts = 1,920 Watts
    Your proposed 3x 175 Watt array will output (roughly):
    • 3 * 175 Watts * 0.77 panel+controller derating * 5 hours of Summer Sun = 2,022 Watt Hours
    At 40a*48v, the motor would drain a day's harvest in ~1 hour +/-.

    At 40a*12v, the motor would drain a day's harvest in ~4 hours +/-.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,109 ✭✭✭✭✭
    #4
    What model MPPT CC are you using? Hopefully it has a 150 max Voc. rating. You need higher voltage than your 3 panels can produce Do you have room for 3 more panels?

    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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