How Does a Battery Charge in a Running Car?

A car battery uses direct current to power low-voltage electrical systems, provides the initial charge that a vehicle needs to start and acts as an energy regulator. Once a car is running, most of the electrical systems are powered by the alternator, which also charges the battery.

Misconception

Many people believe that once an engine is running, you can pull the battery and the vehicle will continue to run with no problems. This may have been true about automobiles in the past, but modern vehicles and their many electrical devices require the presence of a charged battery and working alternator to run.

Alternator Function

The main parts of the alternator are the stator, rotor and diode. Once started, the alternator powers the car by converting mechanical power to electrical power via a belt on the engine crank shaft. The belt causes the rotor to spin which, in conjunction with the stator, generates an alternating electrical current (AC).

Charging the Battery

Since batteries cannot use an alternating current charge, the energy generated by the alternator must first be converted to a direct current charge. This takes place in the alternator diode, which stores and converts the AC to DC and sends the usable power back to the battery.

References

• Standard Automobile Alternator