Black magic fan popping fuses suddenly

Have you bench tested the fan?
Are any power connections loose?
What size fuse are you using?

sounds like the fan motor could be going bad if you are blowing the fuse from battery power and there are no shorts to ground.

fuse

If you don't solder every wire and terminal connection you will have sparking at loose connections because of the high amp surge when the fan turns on. I have the flexalite black magic extreme #185 fan and the controller that comes with this fan is garbage, it allows the fan to turn on with full power and the amp surge is to much, get the "VSC" variable speed controller from flexalite, it has the soft start circuitry, the fans turn on at 40 percent power and slowly gets up to 100 percent power when needed for cooling. The vsc controller also regulates the temps much better than the china controller that comes with the black magic fan.