Pv volts vs battery volts

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ericarsenault
ericarsenault Registered Users Posts: 5 ✭✭
in Off Grid Solar & Battery Systems #1

Hello all, happy to have found this place :) My question: can I have a 48v panel setup to charge a 12v battery bank with a Mppt controller?

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
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    The short answer is generally yes, but you might want to post the specifics (panel, controller, battery specs).

    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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  • ericarsenault
    ericarsenault Registered Users Posts: 5 ✭✭
    #3
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    Hi Estragon, the specifics:

    Conerra onmppt124/60A contoller

    16 genesis 150AH 12 volt gell batteries

    10 270W , 24V panels in mixed series/parallel hook up to give 48V

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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #4
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    You have too large an array to effectively use that charge controller to charge a 12 volt battery bank.

    Do you already have a 12 volt inverter?

    16 - 12 volt batteries all in parallel would be very difficult to keep each battery sharing the load equally. In general, I don't like more than 2 strings in parallel. If you ran a 48 volt system voltage it would be 4 strings of 4 batteries. Not ideal, but better than having 16 batteries all in parallel.

    Charge controllers are pretty much universally rated at output amperage. Most can output at different voltages. I could not find your controller perhaps the name is not spelled correctly.

    With an array of 2700 watts, you will have a potential normal output at 12 volts of 2700 x .75 (NOCT)= 2025 watts. 2025watts ÷ 12volts = 168 amps so more than your charge controller can handle

    but at 48 volts 2025 ÷ 48 = 42 amps well within your charge controller 60 amp ability.

    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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  • billybob9
    billybob9 Registered Users Posts: 141 ✭✭
    #5
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    I will mention one more thing. Always connect your battery to your controller then to your panels.

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #6
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    You may also have some charging current limits too. Many GEL batteries in North America have a 5% maximum rate of charge (vs the 10-15%+ for other styles of lead acid batteries). If you charge them too quickly, they can develop gas pockets in the GEL and reduce their capacity/current capability:

    • 16 * 150 AH * 0.05 rate of charge = 120 Amps suggested maximum for many GEL type batteries
    • 120 Amps * 14.2 volts charging * 1/0.77 typical panel+controller derating = 2,213 Watt array (really 1x 1,106 Watt arrays, one for each controller)

    And if you have 60 Amp charge controllers, 2x of those would supply 120 Amps.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
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    In addition to considering comments above, you may also want to confirm whether the batteries are in fact GEL type (acid is thickened into a sort of paste or gel), and not AGM (acid is Absorbed into a fibreGlass Mat). Both are valve regulated lead acid, but often have different maximum (absorb) charging voltages. The listing I found for the 150ah genesis suggests AGM.

    Whichever type you have, you'll want to be sure the controller can be set for the correct voltage for your bank. I also couldn't find anything online for the controller.

    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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  • ericarsenault
    ericarsenault Registered Users Posts: 5 ✭✭
    #8
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    Thanks guys for your information. The controller is a ONMPPT124/60A

    you can find info at: www.vde.com.mx

    It is sold in Mexico as this solar system is in Mexico ...

    The Batterries are Genesis 12TD150F , and are non spillable , so could be they are not gell. ( I’m a newbie by the way)

    So it seems this is not a good setup..

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #9
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    The batteries do appear to be AGM, but are designed for telecom use, in which the battery spends most of its life on float, with few or no deep discharges. It may not last as long in a regularly deep cycled application as a battery designed for regular deep cycling.

    As @Photowhit noted, 16 batteries in parallel could be a problem. You may want to read this for parallel wiring tips.

    http://www.smartgauge.co.uk/batt_con.html

    I don't speak Spanish, but the controller appears to spec an array size limit of 800w for 12v nominal bank.

    If you could outline your needs/expectations from the system (eg daily and peak loads, grid/generator power available, etc), we may be able to give some opinions on how/if to make what you have work as well as possible.

    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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  • ericarsenault
    ericarsenault Registered Users Posts: 5 ✭✭
    #10
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    You guys are amazing!!! Thanks:))
    So, the Batterries are not gell as I thought, they have the mats inside... so I will change the settings. I am heading back home tomorrow ( Canada), so I don’t have the time to rewire the setup. The battery bank is doing not so bad, lowest voltage is 12.5 in early morning. Estragon you seem to right about the controller not charging more than 800 watts, the max it charges is 917 watts... the strange thing is what the controller displays:

    panel voltage 65.4
    potencia of charge 853w
    current of charge 59.6A
    battery voltage 13.7v

    I don’t get the math...
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #11
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    Panel voltage is the input voltage

    potencia of charge is what the controller is using

    Current of charge is what it is outputting, it's a 60 amp charge controller putting out at max

    Battery voltage is actually a bad term, but it's the voltage the controller is putting out so 'system voltage' would be better.

    Amps x volts = watts, so it's out putting 59.6 amps x 13.7 volts = 817 watts so a bit less than the wattage the controller is using 817/853=96% efficient at converting the incoming voltage at that wattage to a voltage needed to charge your battery bank.

    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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  • ericarsenault
    ericarsenault Registered Users Posts: 5 ✭✭
    #12
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    Nice, now I understand, thanks mate. So If I understand correctly, even though there is 2700w of panels, the controller only uses a fraction of the watts available because it is charging a 12v battery bank and is limited to 60amps at 12v. So, to use the full potential of the panels the battery bank should be connected in 48v or to have 2 more controllers with its own  set of panels.
    This place is a camping, all the light are 12v leds ( hundreds of them). To switch the battery bank to 48v would be a huge task of changing all lights and wires. Are there good stepdown transformers 48v-12v ? 
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #13
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    I suspect you can find good DC to DC converter, I've never needed them, but hear about them. @BB. will likely know about the availability, Do you know what the total wattage you need is?

    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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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #14
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    Samlex is a good source for DC - DC converters, have used them with no complaints, probably not the cheapest but cheap not good, good not cheap.
    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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