EDIT: just realized rereading that you meant the fuse in the Fluke meter.
I did actually make one using wire out of another fuse, but I must've done it wrong, because it didnt' work when I tried it. If I just wrap foil around the dead fuse and put it in, it works, so it's not the meter, just my contruction skills at fault. But I'm not leaving the foil on there, because this is a good meter and I would rather not destroy it--the fuse blew when it was accidentally connected wrong for the setting the dial was at, and I do dumb things like that sometimes...so can't risk losing the meter from it.
The below is about the fuse between charger and battery:
The fuse is there in case the charger has an internal meltdown in such a way that the battery would flow high enough current into it to cause a fire in it (or in it's output wiring), but not high enough current to blow the battery's fuse or breaker (which to run the controller peaks are necessarily much higher than what it might take to do bad things in a failed piece of electronics).
It's also there in case something goes wrong in the charger, wiring or battery itself that causes the charger to output more than 30A, because that's significantly higher than the 20A battery is rated to charge at, and if the charger is outputting that much current, something is wrong with it (it's max should be 11A but this one is maxed at 12A).
I ddin't fuse it for, say, 15A because I might parallel another charger with this one, which would let me charge at the full 20A (or a bit higher) the pack can take, if I need to go on a trip longer htan my range allows but without enough time to charge at only 12A, and also without the need (or space) to put the second battery in. A second charger would be weatherproof even on the outside of the trike, and a second battery isn't and has to go in the cargo/seatbox. (and a second battery requires heavy gauge wiring added while a second charger does not). Also, the second battery weighs several times what the second charger does.
And yes, I am
a mad scientist, most definitely.
Unfortunatley I lost most of my lair's 50s/60s-era lab equipment (like giant old oscilloscopes) in the fire a few years ago, so it doesn't have that forbidden-planet/outer-limits vibe now. Still have the punched-tape-input cabinet computer, though.
As for building things...I couldn't design and build a charger that's anywhere near as good as even something like the HLGs, and these were donated to me, so I use them.
But I *am* building (slowly, as I get or find the parts) a couple of Lebowski controllers to run the trike's rear wheels from. I still have to buy the powerstage units and current sensors; thsoe I'm not going to find used in something I can salvage. :/