I dissasembled a burnt transformer that was taken out of car battery charger recently to find out that the wire on the primary side burnt in half. Although wires are much thinner on primary i dont get it why would it burn out on primary instead on secondary where the load is. Isn't the wattage on primary always the same regardless of the load? Also the side i suppose is secondary(it is probably step down transformer) is center tapped for some reason. For what purpose such a tap could be useful? Thanks for your helpful suggestions in advance.