wire size

belldingerbelldinger Registered Users Posts: 1
I have 12, 290 watt 8.5 amp solar panels wired to a combiner with charge controller 4 feet away what size wire is needed from combiner to controller?
Then battery is 120 feet away, what size wire needed from controller to battery?


  • PhotowhitPhotowhit Solar Expert Posts: 4,768 ✭✭✭✭

    Is the controller near the battery bank? It sounds like the controller is 120 feet from the battery bank? This creates problems for the charge controller to accurately measure the voltage.

    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • Raj174Raj174 Solar Expert Posts: 648 ✭✭✭✭
    Hi belldinger,

    The charge controller really needs to be close to the battery bank, to avoid unacceptable voltage losses and as Photowhit said, so the charge controller can accurately measure the battery voltage. The usual solution for this is to wire the panels in series to achieve higher voltages and cable the distance from the combiner to the charge controller with much lower voltage loss.

    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 207AH LiFePO4 no BMS, 4500W genset.
  • BB.BB. Super Moderators, Administrators Posts: 28,176 admin
    What charge controller do you have (MPPT, PWM, rated input voltage, rated output current, etc.). Link to controller info is OK.

    What is your battery bank (bank voltage and AH rating)?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • GreenPowerManiacGreenPowerManiac Solar Expert Posts: 453 ✭✭✭
    Over 100' distance between you're going to loose voltage around .5 - 1 volt unless...........You could try using the largest wire the controller and combiner allow.  My controllers use a max wire of 14 gauge.   For your greater distance, try using 14 (or whatever yours allows) gauge stranded wire before moving anything.  Compare the loss of power at the batteries & at the controller for total loss then.

    Since electricity travels on the outside of the copper/aluminum wires, the stranded should be able to cut the voltage loss with extra distances and be more flexible to work with.   Solid wiring won't cut it.  
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  • BB.BB. Super Moderators, Administrators Posts: 28,176 admin
    Actually, the "skin effect" where electron flow moves to the outside diameter of the wiring is frequency dependent (higher frequency, more pronounced the skin effect). However, for "pure dc", there is no skin effect.

    Skin effect - Wikipedia
    Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor, and decreases with greater depths in the conductor. The electric current flows mainly at the "skin" of the conductor, between the outer surface and a level called the skin depth. The skin effect causes the effective resistance of the conductor to increase at higher frequencies where the skin depth is smaller, thus reducing the effective cross-section of the conductor. The skin effect is due to opposing eddy currents induced by the changing magnetic field resulting from the alternating current. At 60 Hz in copper, the skin depth is about 8.5 mm. At high frequencies the skin depth becomes much smaller. Increased AC resistance due to the skin effect can be mitigated by using specially woven litz wire. Because the interior of a large conductor carries so little of the current, tubular conductors such as pipe can be used to save weight and cost.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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