Breakers and Fuses..?? Distance from battery or charge controller..??

ywhicywhic Solar Expert Posts: 621 ✭✭
1st.. its a 12v solar panel system..

I have my 250 AMP ANL fuse from my 12v battery bank to my 2000w inverter about 8" from the battery on the 3/0 wire, then another 25" up the lead to my BlueSea marine battery switch, then over to the inverter about 11"..

For the 6 AWG wire coming from the solar charge controller (MorningStar TS-45) to the battery bank what should be the distance on that lead from the battery for the proposed 60 amp breaker I'm going to be installing??

Does it have to close to the battery like the inverter one?? or should it be closer to the charge controller since thats the originating power source per se' ?? or is this breaker for back-feed up from the battery??

I got 5' (max) of wire to go from the controller down to the battery bank.. but just would prefer to mount this breaker on the wall.. vs. dangling..


  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Breakers and Fuses..?? Distance from battery or charge controller..??

    i'm pretty sure this stuff has been covered already for you. i will summarize to say that you need to start figuring it out for yourself with a v drop calculator rather than start another post. in general, you will have differing sections in a system like but not limited to pv to cc, cc to battery,and battery to inverter; but do understand that each section's losses are additive and that means each v drop % loss in each section gets added together. this includes everything in a system including the little pigtail wires on the pvs. in total it is not advisable to exceed 5% (by nec unless they changed it) for all of the losses, but we strive to do even better than that because of the expense pv systems present. often we cite 2% or 3% in total as being better goals. it isn't wise to skimp on a wire size because it may cost more and have the lost power over the system lifetime actually to be more costly to you.
  • ywhicywhic Solar Expert Posts: 621 ✭✭
    Re: Breakers and Fuses..?? Distance from battery or charge controller..??


    I had already figured my wire out:

    1.88% from solar panels to combiner (10 awg)
    0.61% from combiner to the controller (8 awg)
    1.22% from controller to the battery bank (6 awg)
    0.74% from battery bank back to the inverter.. (3/0 awg)

    The question is should the breaker going to the battery bank from the charge controller be near the controller, or the near battery bank..

    I also asked this question as it seems like many (currently) are just behind me in the build process and I'm trying to help them..
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Breakers and Fuses..?? Distance from battery or charge controller..??

    ok al, sorry for any misunderstandings. one should keep fusing as close to the battery as possible seeing as how the battery is capable of large current surges along the wires. current from solar is limited and less threatening if a short occurs as the wiring can handle that.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Breakers and Fuses..?? Distance from battery or charge controller..??

    Here's a longer and probably more confusing answer for you, Al. :p

    Electrically it does not matter where the protection goes in a circuit as once it is tripped the circuit is inactive (no current flowing). It can even go on the negative side.

    Good practice, however, dictates certain wiring conventions designed to prevent additional problems from cropping up. One of those conventions is to always put the protection on he positive side. This is because many devices have negative to ground connections which could result in the current finding an alternate path should the fuse blow/breaker trip.

    Another convention is to put the protection as close to the power source as possible to prevent "dangling live wires". This is why the battery to inverter circuit fuse should be close to the battery: shortens up the length of the still live portion of the positive wire.

    When dealing with both the in and out of the charge controller this issue gets a bit fuzzy, as both sides have two potential power sources (true of any charging circuit). You would think of the controller as being the source in respect to the battery, but it is equally true that battery Voltage finds its way back to the controller (otherwise that wouldn't function).

    If the protection on this circuit should trip, the controller's output will be minimal because the other power source is the panels and they are a current source: no circuit = no power flow as far as they are concerned.

    The battery does not function that way. It always has Voltage and current potential, which is why the inverter fuse should be near it. So technically the controller fuse should be as well. But in practical terms it isn't that risky to put it in a convenient location, and almost everyone puts them near the controller even though this is, strictly speaking, not the safest practice. If the batteries have terminal fusing that eliminates the issue.

    The input side of the charge controller has the same issues, although the risks are greatly reduced because the controller should block battery Voltage from leaking back to the panels and, as mentioned, the panels themselves will only output power when a circuit is present. On their own, panel wires are quite harmless. Can't say the same about wires coming off a battery.

    Someone will probably disagree with this. His last name probably starts with the letter 'W'. :p (JOKE)
  • ywhicywhic Solar Expert Posts: 621 ✭✭
    Re: Breakers and Fuses..?? Distance from battery or charge controller..??

    I decided to go 20" from the battery and then 40" (max) to the controller.. so the breaker will be nearer the battery (just about next to the inverter on the height scale)..

    Thank you for clarifying.
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