Car alternators are great for charging the batteries in cars, but not so good outside the car. The reason for this is in a normal generator you would have a permanent magnet or several permanent magnets in the armature. The coils of wire collect the magnetic field and turn that into electricity. Car alternators are designed with electro magnets and need voltage from the battery to start to generate electricity. the car engineers have done this so they can turn on the alternator when they need to and off again when the battery is charged and to prevent overcharging the battery. Here are a few videos on how to convert a car alternator so that it can be used in a wind turbine. Installing a strong Neodymium magnet will give a lot more flexibility in power generation.