Back to the drawing board

sprintmansprintman Registered Users Posts: 16
Well not all the way back. The panels I was going to get are now sold out.
It was to have been 3- 210w 33.2voc 7.9imp panels in series to an mppt controller and then to 4- 6v 225 amp hour batteries. (polycrystaline cells)

Now I have found 4-175 watt 44.2voc 4.95imp (mono crystaline cells) same charge controller (outback flexmax 60 mppt) same 4 batteries but two sets of two panels in series and then the two sets paralleled.

How does that sound in comparison?

What size wire would be best for a 25 foot run between panels and charge controller?

Thanks in advance!


  • BB.BB. Super Moderators, Administrators Posts: 30,712 admin
    Re: Back to the drawing board

    For a 12 or 24 volt battery bank, those would be a good choice.

    If this was a 48 volt battery bank--I am guessing you are looking at Vmp around 70 volts--Should be just good enough. But three panels may be too much (if you are in a cold area).

    Assuming 10 amps on one pair of 25' one way run wires. 3% drop would be 2.1 volts; 1% drop would be 0.7 volts. Using this generic string calculator:
    • 14 awg => 1.5 volt drop
    • 10 awg => 0.6 volt drop
    With 2 in series, and 2 strings in parallel, you would not need a combiner box/fuses/breakers (3 or more parallel strings should have a combiner box+breakers/fuses).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sprintmansprintman Registered Users Posts: 16
    Re: Back to the drawing board

    The vmp per panel is 35.2 so your guesstimate of 70 is dead on!
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