Make sure the pulleys don't have any nicks, gouges, or worn out spots in them that can damage the belt. Make sure everything is turning so the belt doesn't stop moving and burn through. In addition to being too tight, if the belt is too loose it will flop around and possibly climb the side of a pulley or catch on something.
I do not think the dia. of the pulley will do anything must be an issue. Back up and look again close. Feel the bearings in the alternator. Got to be something you have missed. Piece of belt in the pulley??