can you use a car alternator as a generator

[MalachiDella]

Technically, yes, you can use a car alternator as a generator, but it's not a simple or efficient plug-and-play solution. An alternator is designed to produce electricity while being spun by the engine, which is already burning fuel. To use it as a standalone generator, you need a separate power source to rotate it, like a gasoline engine, and you must address key limitations like its inability to produce useful power at low RPMs and the need for an external 12V source to energize its field circuit.

The core challenge is that an alternator doesn't generate electricity from nothing; it requires mechanical energy input. Simply connecting it to a bicycle or a hand crank won't yield meaningful power. You need a substantial prime mover, such as a small gas engine, to spin it at several thousand RPM. Furthermore, a standard alternator is a three-phase AC device whose output is immediately rectified to DC for charging a battery. To get standard 120V AC household power, you'd need a complex setup involving a power inverter.

The following table compares a typical car alternator's output to a common small inverter generator, highlighting key performance differences:

Feature	Typical Car Alternator (e.g., 100A model)	Small 2000W Inverter Generator
Usable Power Output	~600-800W at 2000+ RPM engine speed (after efficiency losses)	1600W (rated), 2000W (max)
Voltage Output	~13.5-14.5V DC (requires inverter for AC)	120V AC (standard household outlets)
Fuel Efficiency	Low (when paired with an inefficient small engine)	High (optimized engine-generator pairing)
Noise Level	Very High (engine and alternator whine)	Low to Moderate
Cost & Complexity	High (requires engine, mounting, wiring, inverter)	Low (single, integrated unit)
Voltage Regulation	Good (for a 12V battery system)	Excellent (clean, stable power for electronics)

For a reliable, safe, and efficient source of backup electricity, a purpose-built generator is overwhelmingly the better choice. The DIY alternator-generator project is more of a technical exercise for understanding electrical principles than a practical power solution.

[VonRiley]

I tried this once in my garage. You need another engine, like from a lawnmower, to spin the alternator fast enough. Then you have to figure out the wiring to get the alternator to "excite" and start producing power. Even if you get it working, it's incredibly loud, inefficient, and only gives you DC power. For the money and hassle, you're way better off just buying a small, quiet inverter generator. It's not worth the headache for the little power you get.

[MacJack]

Think of it like this: an alternator is a component, not a finished product. A coffee maker has a heating element, but you wouldn't try to use just the element to brew coffee. An alternator needs the car's engine, computer, and battery to function correctly. On its own, it's incomplete. While a fascinating mechanical project, the result is impractical for actual power needs compared to a dedicated generator designed from the ground up for efficiency and safety.