Re: battery fuses
Assuming these are 420 AH flooded cell batteries, the maximum useful surge current of C/2.5 would be:
- 420 AH * 1/2.5 = 168 Amps
You have 7 parallel strings of batteries driving a 2,500 watt 12 volt inverter (assuming 85% efficient inverter):
- 2,500 watts * 1/10.5 volts * 1/0.85 eff * 1.25 NEC factor = 350 Amp Circuit
For a battery bank with lots of paralleled strings--I would, personally, try to design for 50% of the load to be carried by one battery (lots of paralleled batteries do not always share current well--designing fusing to 50% will prevent blowing fuses unnecessarily vs 1/7th of load or 50 amp fusing):
- 350 Amps * 0.50 = 175 Amp circuit per battery.
Depending on lots of things, a 1/0 cable is good for ~150-170 amps or so (even upwards of 245 amps in free air--NEC is pretty conservative).
So--I would probably pick the 175 amp fuse myself... This will limit issues with false trips if you have current sharing issues (bad cables, cells, etc.) but still protect wiring/batteries from excessive current (you still need to protect wires leaving the + bus bar/battery common point).
Since this is an old battery bank and system--Before you put a lot of money into the system wiring up the fuses/parallel battery bank... Does this make economic sense to you? New battery bank, new inverter, changing to 24 or 48 volt bank?
20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.