Originally Posted by Drift Woods
The installation instructions call for a fuse between the panels and the controller
, and one between the controller and the battery. For wire sizing per run length I've been using the attached chart. It calls for a minimum 6 awg from the charger to the battery @ 40 amps in a critical circuit. The 4 awg installed according to the chart is good for 60 amps in a critical circuit.
I do think adding a small bus bar is a smart idea. I may decide to add two more panels and a second controller later on.
Thanks for the help, Woody
This is a land based NEC requirement where panels will be run at significantly higher voltages often with micro inverters right at the panel.... Your panels are "self-limiting
" and thus any fuse and wire that can handle the loads, and not induce performance robbing voltage drop, won't trip on the PV side of the controller because the panels can't develop enough short circuit current
to do that...
The battery is the current source
you are protecting the wires from and a fuse is a safety
requirement, preferably within 7" of the battery positive post....
So long as the charger wire is large enough to handle both charge sources at once, with minimal voltage drop, adding positive & neg busbars at the charger is a suitable choice, just be sure they are covered.
With 4GA wire at 18' to the bank the round trip circuit length is roughly 36'. 36' of 4GA wire at 20A & 14.4V will net you about a 1.3% wire voltage drop
excluding connections/terminations. Even adding 200W of solar
to the 20A charger, and calling it a max potential of about 32A, your voltage drop in a 36' 4GA circuit at 14.4V is still about 2%...
Also the chargers AC terminations (butt splices) should be made inside the charger case, or in a j-box. The white wire connected to the chargers case/frame grounding point should be no more than one GA smaller than the DC charging
wires. It should also be green or green with a yellow stripe and run directly back to the ships ground bus.