You can technically power a house with a car alternator, but it would be an inefficient and impractical way to do so. Car alternators are designed to charge a car's battery while the engine is running, and they typically have an output of around 12-14 volts. A typical household circuit runs on 120 volts, so you would need at least 10 car alternators to power a home. Plus, car alternators are not designed to run continuously for long periods of time, so they would overheat if used to power a house 24/7. If you were in a pinch and needed to generate power for your home using a car alternator, you could rig up a system where the alternator charges a bank of batteries that then powers your home's electrical system - but again, this would be very inefficient and impractical.