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How do car alternators work? Answered

I am working on way to charge electronics at long festivals.  There is no electricity and then my camera dies.  My solution is to bring a car battery and charge USB devices using car power/usb power adapter.

My questions is about charging car batteries.  I noticed that the highest charge setting on my wall-power car charger is 6 amps.  A car alternator on the other hand supplies 65 amps.  Why such a huge difference?  When you jump start dead car battery and then charge the battery with the car running the alternator is the battery really charging at 65 amps?  That is 10 times more current than from a wall charger.



4 years ago

Automobile alternators have two windings, field (stationary) and rotor. Electromagnets are stronger and controllable. By varying the current in the field windings, the alternator can put out whatever current is needed, up to whatever limits the heat from this can be expelled and the wires carrying capacity. The car engine has plenty of horsepower to spare. It takes 2 HP + to run your 65 amp alternator. The most a person pedalling a bicycle genset can do for any extended length of time is about 100 watts. You can buy rechargeable battery packs and carry a lot of those easier than a car battery.

For about $100 you can get a cheap hand carry camping generator that will run all day on a tank of gas.


4 years ago

The alternator not only charges your battery but also runs everything else electrical in your car.

Take a modern car with some extras and you will see it has an even bigger alternator installed.

If you want a 12V battery to charge you stuff you might want to decide on a deep cycle battery - they don't provide the huge currents needed to start a car but can be discharged lower.