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Need clarification on wire size for battery to charge controller

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  • Need clarification on wire size for battery to charge controller

    I'm trying to make a portable solar power bank with a 100 watt renogy panel, a 20 amp PWM controller, and a deep cycle battery from my boat to charge gps, headlamps, and power a quad band radio when needed. I understand figuring out gauge size for panels to charge controller but I can't seem to find a clear explanation of wire size between battery and charge controller. The battery will be right next to charge controller and panel up to 20ft away.

    From what I gather from the calculators I should be ok with 20ft of 12 awg wire from panel to controller. I think 12 awg should be fine for controller to battery. I will be running an old maxx 400 watt inverter just to charge some devices that only have AC. Am I right to make the battery to controller calculatiion based on the max draw from the load side? I'm a little confused because some battery chargers with alligator clips only have tiny wires and they charge fine and some people say to get huge wires just like a vehicle uses which don't even look like they fit into the 20amp controller I'm looking at on amazon.

    I already ordered a 20awg panel mount sae outlet for a box and and some 12awg sae connectors to use inside the box to easily disconnect components. Now I'm wondering if 12awg was enough and also if sae was a good idea because they aren't that cheap and not easy to find stuff like sae panel mounts.

    I'd appreciate some help.

  • #2
    Hello badcrc and welcome to Solar Panel Talk.

    The size of the wire between the charge controller and battery needs to be at least big enough to handle the maximum amp output of the CC which is 20amps in your case.

    If you keep the battery relatively close to the charge controller a pair of #12 awg wires will be enough to handle that 20amps. You can always go bigger but I would imagine that the terminals on that CC can't handle wire bigger than # 10awg.

    Remember to install a fuse in the wire between the CC and battery on the Plus side if you have grounded the Negative side. If not then install fuses for both the Pos and Neg wire.

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    • #3
      Originally posted by SunEagle View Post
      Hello badcrc and welcome to Solar Panel Talk.

      The size of the wire between the charge controller and battery needs to be at least big enough to handle the maximum amp output of the CC which is 20amps in your case.

      If you keep the battery relatively close to the charge controller a pair of #12 awg wires will be enough to handle that 20amps. You can always go bigger but I would imagine that the terminals on that CC can't handle wire bigger than # 10awg.

      Remember to install a fuse in the wire between the CC and battery on the Plus side if you have grounded the Negative side. If not then install fuses for both the Pos and Neg wire.
      OK thanks for the info.

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