Alternator: Device that generates the electric current that charges the battery.
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It can be found next to the engine and it is activated by the poly-V belt. While the engine is running, the alternator will charge the battery. Inside of it there is a voltage regulator that limits the electric tension that will be delivered.
I changed the alternator recently when I try to start the car with key it doesn't start , t don't know what the broplem there are no light or power in the car