You can get 120 volts or more out of an alternator simply by bypassing the voltage regulator, it just depends on at what level you want to regulate the voltage. The limit on the power ( KVA ) rating of the alternator is the size of the wire in the windings. You can increase the voltage, but with the same size of windings in the alternator, you have to proportionately decrease the current to maintain the power rating of the device The advantage of using higher voltages, is that you can run smaller wires and the components are smaller The real problem is, that as the voltage gets higher, the problems of safety become much greater.
