Free Automotive Guide: Starting/Charging System

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starter buttonThe first automobiles ever invented required the use of a large crank handle. It slid onto the end of a shaft which was attached to the front of the crankshaft and protruded dauntingly through the grille. Most crank handles were removable, though some simply folded inward. One thing that they all had in common was they were necessary for getting the car’s engine started. Drivers literally had to work for the pleasure of operating the auto. With the adaptation of battery power to automobiles, came the invention of the electric starter, with a starter button. Next came the keyed ignition switch, initially located in the dash and then in the steering column, for security reasons. Now, cars are equipped with starter buttons, again. This time they are updated with computerized transceivers, which correspond with the driver’s key-fob. Really hi-tech; but did you ever stop to wonder what actually happens when you turn the ignition key or push the start button?

When the driver activates the starter signal from the passenger compartment, several automotive systems are engaged.


The 12-volt automotive system utilizes power from a rechargeable lead-acid type battery, which is normally located under the hood, occasionally in the trunk, at times in the front fender-wells, or rarely in the passenger compartment. The modern automotive starting/charging system uses voltage stored in the battery to crank the engine, operate some electronic devices, and to help initiate ignition spark. The battery is recharged using the vehicle’s alternator, which is driven by the running engine.


The internal combustion engine demands an initial “jolt” in order to crank. This jolt comes in the form of an electric starter. The starter consists of three basic components.

  • The ignition switch is generally actuated using the ignition cylinder with the key or the starter button, in very late model vehicles. Voltage is input to the ignition switch from the battery. When the ignition cylinder is turned, a rod or gear moves the internal components of the switch creating contacts and outputting voltage to various systems. Chief among these systems is the starting system and the starter solenoid, in particular. The ignition switch also outputs voltage to any “switched-voltage” system. For a circuit to be labeled this way means that it only carries voltage when the ignition switch is in the on position. Climate control devices, turn signals, ignition systems, and computer engine control systems are usually powered by switched voltage.
  • The solenoid, which is usually attached to the starter, is supplied with solenoidprimary voltage by a cable that runs directly from the positive post of the battery. Voltage, supplied from the ignition switch, passes through a smaller wire and to the secondary pole of the starter solenoid. The solenoid supplies battery voltage to the starter armature when demand is triggered by voltage supplied from the secondary wire. In addition it pushes the spinning gear upward and into the teeth of the engine’s flywheel. The starter circuit is completed with a ground between the starter housing and the engine block, which is grounded to the battery.
  • The starter armature begins to spin inside of a stator, which attaches to the starter housing, at a high rate of speed once 12-volts are applied to its positive pole. Through the armature there runs a shaft, a small gear slides up and down on the end of it. The gear also turns at the same rate of speed as the armature. Once the spinning gear is pushed forward by the solenoid fork, it meshes with the teeth on the flywheel of the engine, turning the engine. As the ignition switch supplies voltage to the starter solenoid it also supplies voltage to the ignition system, the fuel pump, and the engine control computer (if applicable). Turning of the engine is initiated by the electric starter and once it begins to turn, four-cycle perpetual motion permits it to continue running until it is turned off. (Assuming that it has fuel, ignition, and compression, in correct timing).


The primary purpose of the alternator is that of recharging the battery during vehicle operation. It also supplies the adequate voltage needed to operate other automobile systems such as air conditioning and heating.


brush housing 2
Brushes in Housing





Alternating current is created via a rotating armature inside a stator, which remains stationary inside the alternator housing. The alternating current is passed along through the use of spring loaded “brushes” which keep constant contact with the rotating armature. The brushes have wires attached to the ends which are away from the armature. These wires transport alternating current to the rectifier bridge or diode trio. The alternating current is then converted to direct current by the rectifier-bridge or diodes.

diode trio
Diode Trio

Once converted to direct current, voltage is used to recharge the battery by utilizing a large wire which runs directly from the charging pole of the alternator to the positive post of the battery. Tributaries of this wire, or cable, also provide voltage to the fuse box, relay center, fusible links, control modules, and lighting, depending upon the vehicle year, make, and model.

Voltage from the alternator is regulated using a voltage regulator (if you can believe that). Their purpose of the voltage regulator is to limit the amount of voltage supplied to the battery and other electrical devices. Older vehicles used remotely mounted voltage regulators (pre 1970s). Later, as alternator technology advanced and voltage regulators became smaller, they were built into the alternator housing and now, most late models use the powertrain control module (PCM) to regulate voltage from the alternator.

The alternator uses rotation created by the crankshaft to spin the armature inside of the stator by using a pulley attached to the end of the armature shaft. A drive belt, which is tightly fitted around the crankshaft pulley and the alternator pulley (as well as others), is used to rotate the alternator armature.

  • serpentine beltSerpentine style belts are used on most late model vehicles. This type of belt typically drives every rotational component on the face of the engine. Air conditioning compressors, power steering pumps, smog pumps, and water pumps are all driven using one serpentine belt. Serpentine belts are kept taught using a spring loaded tensioner assembly.
  • Older vehicles were equipped with v-belts. V-belts were used to drive individual components, so multiple v-belts were needed on one vehicle. The alternator had its own belt (which was often routed around the crankshaft, water pump, and alternator), the power steering pump had another belt, the air conditioning compressor had its own belt, and so on. Although it is rare, some vehicles use multiple serpentine belts or a combination of serpentine belts and v-belts.

Blown FuseFuses and Relays

  • Inline fuses are necessary to prevent major electrical damage due to shorted wires or components. Available with various amperage ratings, fuses are designed to “blow” and discontinue the flow of voltage to/from a particular circuit when an electrical short or overload becomes severe enough to demand it. Once a fuse is blown, it must be replaced with a new fuse. Fuses are used today in multiple configurations, as nearly every major automaker is loyal to a particular design. Fuses should always be replaced using the precise amperage rating specified by the manufacturer.
  • Fusible link type fuses “melt” when shorted or overloaded. They are utilized as part of the wiring and must be replaced as such.

    fusible link
    Burnt fusible link
  • Relays are used to off set current that is being sent to a particular device. As voltage is input to multiple poles of the relay (along with a ground signal) contacts inside of the relay are closed. When the contacts are closed voltage is output to the electrical device or system designated.
S.M. Darby

S.M. Darby

I am a freelance author with over 25 years of experience as a professional, ASE certified automotive technician and shop owner, muscle car enthusiast, avid street racer, and classic car restoration specialist.