1999 Plymouth Voyager blows 20 amp engine fuse/looses alter

Kindly put some punctuation in your post so it makes sense, and elaborate on what you've tried so far. What doesn't work when the fuse blows. Does it blow again right away? How do you bypass an alternator? What does "looses voltage then voltage comes back" mean? Give some clue as to where you're measuring this voltage. In the meantime, I'll be thinking about it.