Fuse size to use

I would use no more than a 30 Amp. But the easiest thing to do is measure the current flow on the wire and add a fuse that is about 25% greater than the current flow. You may find that you do not need a very large fuse this way

Plus I would disregard the 80 amp output when considering the fuse size. Its like I have 400 amp service on my house but the largest fuse I am using is a 60 amp split phase and that is for a tankless water heater. I could probably get away with a 150 amp service but it is what it is.
Just because the power is available, does not mean you will use ALL OF IT