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Alternators were first introduced as standard equipment on a production car by Chrysler for the Valiant model in 1960- several years ahead of Ford and General Motors. They replaced direct current generators (dynamos) because they were lighter, cheaper, more rugged and could provide a useful charge at idle speed.


The present-day charging system hasn't changed much since 1960. It consists of the alternator, regulator (which is usually mounted inside the alternator) and the interconnecting wiring. The purpose of the charging system is to maintain the charge in the vehicle's battery and to provide the main source of electrical energy while the engine is running.

The battery is the vehicle’s reservoir of electrical power. Its biggest job is to crank the engine to start the car. The battery also supplies power to the accessories when the engine isn't running. The alternator creates power to recharge the battery by turning mechanical energy from the car's crankshaft into electrical energy. The electronic control unit (ECU), or in older cars, the regulator, acts as a "traffic cop" to control the alternator's output. It senses when the battery needs charging or when the demand for electricity changes.

The alternator is a generator that produces alternating current (AC), similar to the electrical current in your home. This current is immediately converted to direct current (DC) inside the alternator. This is because all modern automobiles have a 12-volt, DC electrical system. It is driven by a belt that is powered by the rotation of the engine. This belt goes around a pulley connected to the front of the engine's crankshaft and is usually responsible for driving a number of other components, including the water pump, power steering pump and air conditioning compressor. On some engines, there is more than one belt and the task of driving these components is divided between them. These belts are usually referred to as the fan belt, alternator belt, drive belt, power steering belt, A/C belt, etc. More common on late model engines is the serpentine belt- one wide belt that snakes around several pulleys in the front of the engine and drives all the components.


Serpentine Belt on 5.7 Engine

On engines with separate belts for each component, the belts will require periodic adjustments to maintain the proper belt tension. On engines that use a serpentine belt, there is usually a spring loaded belt tensioner that maintains the tension of the belt, so no periodic adjustments are required. A serpentine belt is designed to last around 30,000 miles. Check your owner's manual to see how often yours should be replaced.

How Do Charging Components Work?


The alternator uses the principle of electromagnetism to produce current. There are two main components that make up an alternator. They are the rotor and the stator. The rotor is connected directly to the alternator pulley. The drive belt spins the pulley, which in turn spins the rotor. The stator is mounted to the body of the alternator and remains stationary. The stator contains 3 sets of wires that have many loops each and are evenly distributed to form a three phase system.



The rotor contains the powerful magnet that passes close to the many wire loops that make up the stator. When the rotor spins inside the stator, current is applied through a pair of brushes that make constant contact with two slip rings on the rotor shaft. This causes the rotor to become magnetized. The alternating north and south pole magnets spin past the three sets of wire loops in the stator and produce a constantly reversing voltage in the three wires (i.e., alternating current).



Alternating current is converted to direct current by using a series of 6 diodes that are mounted in a rectifier assembly. A diode allows current to flow only in one direction. If voltage tries to flow in the other direction, it is blocked. The six diodes are arranged so that all the voltage coming from the alternator is aligned in one direction thereby converting AC current into DC current.


Rectifier Assembly

Current to generate the magnetic field in the rotor comes from the ignition switch and passes through the voltage regulator. The current is connected, from the regulator to the spinning rotor by wires connected to two spring-loaded brushes that rub against two slip rings on the rotor's shaft. The voltage regulator monitors the voltage coming out of the alternator and, when it reaches a threshold of about 14.5 volts, it reduces the current to weaken the magnetic field. When the voltage drops below this threshold, the current to the rotor is increased.

There is another circuit in the alternator to control the charging system warning lamp that is in the dash (see below).

Voltage Regulator

A voltage regulator regulates the charging voltage that the alternator produces to protect the electrical components throughout the vehicle. It can be mounted inside or outside of the alternator housing. If the regulator is mounted outside (Ford products) there will be a wiring harness connecting it to the alternator.


Voltage Regulator

The voltage regulator controls the field current applied to the spinning rotor inside the alternator. When there is no current applied to the field, there is no voltage produced from the alternator. When voltage drops below 13.5 volts, the regulator will apply current to the field and the alternator will start charging. When the voltage exceeds 14.5 volts, the regulator will stop supplying voltage to the field and the alternator will stop charging.

Warning Lamp

There is also a system to warn the driver if something is not right with the charging system. This could be a dash mounted voltmeter, an ammeter, or more commonly, a warning lamp. This lamp is variously labeled "Gen" Bat" and "Alt." If the warning lamp lights up while the engine is running, it means that there is a problem in the charging system, usually an alternator that has stopped working. The most common cause is a broken alternator drive belt.

A charging system warning lamp is a poor indicator of problems in that there are many charging problems that it will not recognize. If it does light while you are driving, it usually means the charging system is not working at all. The most common cause of this is a broken alternator belt.


Dodge Challengers, in addition to warning lights, are equipped with an EVIC display. The displays have evolved over the years, but they all provide accurate voltage readings.




If the charging system stopped working, the battery's charge would soon be depleted, leaving the car with a "dead battery." If the battery is weak and the alternator is not working, the engine may not have enough electrical current to fire the spark plugs, so the engine will stop running.

However, if the battery is "dead", it does not necessarily mean that there is anything wrong with it. It is just depleted of its charge. It can be brought back to life by recharging it with a battery charger, or by running the engine so that the alternator can charge it. That being said, if your battery is 4-5 years’ old, it has probably outlived its useful life and needs replacement.

A modern automobile has a 12 volt electrical system. A fully charged battery will read about 12.5 volts when the engine is not running. When the engine is running, the charging system takes over so that the voltmeter will read 14 to 14.5 volts and should stay there, unless there is a heavy load on the electrical system such as wipers, lights, heater and rear defogger all operating together while the engine is idling at which time the voltage may drop. If the voltage drops below 12.5, it means that the battery is providing some of the current. You may notice that your dash lights dim at this point. If this happens for an extended period, the battery will run down and may not have enough of a charge to start the car after shutting it off. This should never happen with a healthy charging system

What Can Go Wrong?

There are a number of things that can go wrong with a charging system:

  • Insufficient Charging Output
  • Too much voltage
  • Worn Bearings
Repairing Charging System Problems

The most common repair is the replacement of the alternator with a new or rebuilt one. A properly rebuilt alternator is as good as a new alternator and can cost hundreds less than purchasing a brand new one.
(Note- The OEM alternator is re-manufactured, comes with a 12-month warranty, and costs $450 with the old core. A less expensive choice is the AC Delco re-manufactured Nippondenso unit, with 12 month warranty, for $300).

Most alternators, like the one on a 5.7 Hemi (see photo, above), are easily accessible and visible on the top of the engine. Others are more difficult to reach, like the bottom-mounted one on a 6.1 Hemi.

In some cases, if the problem is diagnosed as a bad voltage regulator, although the , regulator can be replaced, it is often not cost effective to do so.
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