With full battery voltage to the alternator field and the engine RPM up around, say, 2000, the alternator will generate well over 100 volts. You used to be able to buy a kit to install in your vehicle that cut the regulator out of the circuit and disconnected the alternator output from the battery, and with some means of keeping the RPM fixed, you could run power tools (with series-wound motors only, since it's 110V DC), lights, and so on until the battery got weak and you had to switch back to recharge it. I had one of these things, andbefore i installed it I opened it to see why it cost so much. A DPDT toggle switch, a neon light with dropping resistor that fired at
110V so you knew when you were at the right RPM, and a household electrical outlet. Total cost no more than five bucks back then, maybe ten today. You could even weld with it, though the current rating of the alternator had to be respected. And that's what limits the alternator: current. Too much demand and we burn it out. It really doesn't care about turning out 110 volts if we want it to.The regulator holds the alternator's output voltage constant, and with the battery run down a bit its voltage will be lower so it'll allow more current through it. The current decreased as its voltage rises and opposes the alternator voltage. All the regulator senses (and controls via field current) is output voltage.
Dan