Which device to I use when determining wire gauge and fuse amperage

[thetp23]

I wrapping up my solar system plan for my skoolie and am having trouble figuring out the fuses and wire gauge size on the DC part of my system. I have 2 48v EG4 batteries at 100 ah each. They will be wired in parallel from a 600 amp bus bar. From that bus bar it will go to a 48v to 12v converter that is 100 amp and 1200 w output. Then that will go to another bus bar to distribute power to a 12 circuit fuse panel and a 6 circuit fuse panel. Both panels are 100 amps.

1: For the first stretch (batteries to the converter), do I size my wire and fuse for the 200 ah, or do I take the 1200 watt output for the converter and divide by 48 to get 25 amps for the input side. I'm hoping for the latter, because the difference is 2/0 cable (maybe 4/0) and 250 amp fuse, or 14g cable and 30 amp fuse.

2: For the 2nd stretch, do I need a fuse before AND after the bus bars or on just one side of the bus bar?

 

[sunshine_eggo]

1: 200Ah is a capacity - a quantity of energy, not a current.

Assume it's 80% efficient.

1200W / 48V / .8 = 31.25A

Wire should be sized for this. fuse/breaker should be 1.25X greater (rounded up to nearest common size).

2: Depends.

Every segment of the circuit needs protection. If you use the same size wire on both sides of the bus bar, and there is no possibility of subjecting the wire to higher current, a single fuse/breaker would suffice. The issue is if you have one wire feeding the bus bar, and multiple wires coming off it. All wires must have adequate over current protection (OCP).

 

[thetp23]

1: 200Ah is a capacity - a quantity of energy, not a current.

Assume it's 80% efficient.

1200W / 48V / .8 = 31.25A

Wire should be sized for this. fuse/breaker should be 1.25X greater (rounded up to nearest common size).

2: Depends.

Every segment of the circuit needs protection. If you use the same size wire on both sides of the bus bar, and there is no possibility of subjecting the wire to higher current, a single fuse/breaker would suffice. The issue is if you have one wire feeding the bus bar, and multiple wires coming off it. All wires must have adequate over current protection (OCP).

This is very helpful. Thank you for your response.