Adding a fuse is extra protection for your system. It is meant to protect from system over-voltage or damage from a short circuit. It is not mandatory to have fuses for your system to function properly. However, we do recommend to add fuses to prevent any mishaps.
We recommend adding three separate fuses:
First: between the solar panels and charge controller (MC4 in-line fuse)
Second: between the charge controller and batteries (ANL fuse)
Third: between the batteries and inverter (ANL fuse)
To size the fuse between the solar panels and charge controller we need to find out the amperage going through the line from solar panel to the charge controller. Amperage will depend on the number of solar panels you have on your system and how they are wired (Series, Parallel or Series/Parallel).
Panels connected in series increases the voltage keeping amperage the same whereas when panels are connected in parallel the voltage remains the same while amperage is increased.
For instance, if you have two Renogy 100-watt panels connected in series, each producing 19 volts and 5 Amps under optimum condition, the total output will be 38 volts and 5Amps. We will take the total amperage and multiply it by 1.25 for safety factor(5A x 1.25) giving us fuse size of 6.25A (10A if we round up). Similarly, if you have two Renogy panels connected in parallel, the total output will be 19volts and 10 Amps, so we multiply the amps by 1.25 for safety factor (10A x1.25) giving us the fuse size of 12.5A (15A if we round up).
The second fuse between the charge controller and the batteries should match the amperage of the charge controller. For instance, if you have 40 Amp charge controller, we recommend adding 40 Amp fuse.
The last fuse between the batteries and inverter would depend on the size of inverter and battery bank voltage. The rule to size the fuse is; “Watts/battery voltage” x1.25 (safety factor). For instance, if you have 1000-watt inverter connected to12-volt battery bank 1000(inverter size)/12 volt (battery bank) = 83.33A x 1.25(safety factor) = 105 Amps, so would recommend a 150A fuse.
We recommend installing all the fuses on the positive line of the system. Mc4 in-line and ANL fuses are available on our website.