Re: Xantrex PROWatt SW 600 Inverter fuse size & surge question
Trust in the company and use an 80 Amp fuse.
There's lots of things to consider when sizing fuses, not the least of which is the NEC derating. 60 Amps * 1.25 = 75 Amps, nearest equivalent being 80 Amp.
Otherwise you end up doing calculations like maximum power * minimum input Voltage and wondering about how long the particular fuse will hold if it is over current (and by how much) and you might put in a fuse which will protect it against exceeding 1200 Watts / 10.5 Volts but that's not really the size you want to use for continuous operation.
As for start-up surge ... that's more tricky. First problem being electric motors aren't easy to predict in their start surges and this is not something that can be easily measured because it happens so quickly. That said, the second problem is how long the inverter can maintain its surge rating as sometimes the motor start-up does not happen that quickly. Personally I don't like to depend on surge ratings for anything other than "whoops! Everything turned on at once!"
Another problem (as if you needed more to worry about) is the ability of the battery bank to handle the surge current demand. This is especially problematic on 12 Volt systems as the ratio between the DC side and the AC side is approximately 10:1. That 1200 Watts can be 120 Amps DC @ 10-ish Volts. It is at least 100 Amps. If the wiring offers too much resistance, the Voltage at the inverter can drop below its minimum and the thing will shut down. The length of the battery wires will affect this too, as will imperfections in connections.
Slight differences on the DC side make big differences on the AC side:
80 Amps (fuse rating) @ 12 Volts nominal (lowest you really want the battery to get) = 960 Watts but at 12.5 Volts it's 1000 Watts and at 13.8 it's 1100 Watts. Use the biggest wire you can fit & afford for the DC, use the 80 Amp fuse, and hope the start-up isn't well above the inverter's maximum.
Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.
Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps