The charging system provides electrical energy for all of the electrical components on the vehicle.
The main parts of the charging system include:
• the battery
• the alternator
• the voltage regulator, which is usually integral to the alternator
• a charge warning, or indicator light
• and wiring that completes the circuits.
The battery stores an electrical charge and provides the elec-trical energy for starting.
Then, once the engine is running, the alternator – which is connected to the engine via a drive belt – converts some of the mechanical energy of the engine into electrical energy to sup-ply all the electrical components of the vehicle.
The alternator also charges the battery to replace the energy used to start the engine. The voltage regulator pre-vents over-charging.
1. The voltage ………………………… prevents over-charging.
2. One of the main parts of the charging system is a charge warning, or ………………………… light.
3. Once the engine is running, the ………………………… – which is connected to the engine via a drive belt – converts some of the mechanical energy of the engine into electrical energy to supply all the electrical components of the vehicle.
Student/Intern information:
Name Date Class
Handout Activity: HA773
Summary The charging system allows for a means to recharge the battery and allow for electrical usage of components in the vehicle.
The alternator converts mechanical energy into electrical en-ergy, by electro-magnetic induction.
In a simple version, a bar magnet rotates in an iron yoke which concentrates the magnetic field. A coil of wire is wound around the stem of the yoke. As the magnet turns, voltage is induced in the coil, producing a current flow. When the North pole is up, and South is down, voltage is induced in the coil, produc-ing current flow in one direction.
As the magnet rotates, and the position of the poles reverses, the polarity of the voltage reverses too, and as a result, so does the direction of current flow.
Current that changes direction in this way is called alternating current, or AC. The change in direction occurs once for every complete revolution of the magnet.
1. It converts mechanical energy into ………………………… energy, by electro-magnetic induction.
2. Current that changes direction in this way is called ………………………… current, or AC.
3. Inside the alternator, a bar magnet rotates in an iron yoke which concentrates the ………………………… field.
Student/Intern information:
Name Date Class
Handout Activity: HA774
Summary In the alternator a magnetic field rotates and the conductors are stationary. Mechanical energy is converted to electrical energy by electromagnetic induction.
The value of the electromotive force (EMF) induced by an alter-nator depends on the strength of the magnetic field. Increasing the strength of the magnetic field, increases the value of the induced EMF.
It also depends on the speed at which the magnet rotates, and on the number of turns of wire on the stationary coil.
A single phase model has only 1 stationary coil. In a real automobile alternator, 3 separate coils of wire, or phase wind-ings are common. The windings are arranged so that when the magnet is rotated, it generates a 3-phase output. The phases are equally spaced in time, and this results in a phase shift of 120 degrees.
An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to direct current, where the direction of the current stays constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves.
Used generically, AC refers to the form in which electricity is delivered to businesses and residences. However, audio and radio signals carried on electrical wire are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.
1. In a real automobile alternator, 3 separate coils of wire, or ………………………… windings are common.
2. Increasing the strength of the magnetic field, ………………………… the value of the induced EMF.
3. It also depends on the ………………………… at which the magnet rotates, and on the number of turns of wire on the stationary coil.
Student/Intern information:
Name Date Class
Handout Activity: HA775
Supervisor/Instructor information:
Name Signature Date
Score / 3
Summary The value of the induced EMF depends on the strength of the mag-netic field, the speed at which the magnet rotates and the number of turns of wire on the stationary coil.
• A stationary winding assembly, called the stator.
• A rotating electro-magnet, the rotor.
• A slip-ring and brush assembly.
• A rectifier assembly.
• Two end-frames.
• And a cooling fan.
A voltage regulator monitors battery voltage and varies cur-rent flow through the rotor field circuit, and thus controls the strength of the rotating magnetic field. This keeps system volt-age to a safe level.
1. The alternator contains a slip-ring and ………………………… assembly.
2. A voltage regulator monitors battery voltage and varies current flow through the rotor field circuit, and thus
controls the strength of the rotating ………………………… field.
3. The alternator contains a stationary winding assembly, called the ………………………….
Student/Intern information:
Name Date Class
Handout Activity: HA776
Summary The main components of an alternator are the stator, the rotor, a slip-ring and brush assembly, a rectifier, two end-frames, and a cooling fan.
Rectification is a process that converts alternating current (AC) into direct current (DC).
Automotive alternators use diodes in the rectifier assembly. A diode allows current to flow in the forward direction, but blocks the flow of current in the reverse direction.
A three-phase bridge rectifier has six diodes to rectify the total alternator output -
• Three positive and
• Three negative.
One of each is used to rectify current in each of the three-phase windings. The positive diodes let current flow out to the battery terminal B -positive. The negative diodes complete the return circuit from the battery terminal B - nega-tive.
In each revolution of the magnet, the polarity of each phase winding changes, and as a result, the current changes direction. To provide a unidirectional, or DC output, a complete circuit is needed for current to flow when each change in polarity occurs. As the rotor turns, it induces a voltage in the winding, which generates current flow.
Student/Intern information:
Name Date Class
Handout Activity: HA777
Summary Automotive alternators use a three phase bridge rectifier that has three positive diodes and three negative diodes to rectify the AC current in the three phase stator windings to produce a DC output.
In this position, and with this polarity, the current path is as follows: output of winding A, positive diode A, alternator terminal B-positive, battery positive terminal, battery ground [B-negative], alternator ground, negative diode B, output of winding B, neutral or star point.
When the magnet rotates further to this position the polarity of winding A changes. The current path then is: winding A, at star point, winding C, positive diode C, alternator terminal B+, battery positive terminal, battery ground, alternator ground, negative diode A and output of winding A.
As the rotor moves through its various positions, individual phase currents change in magnitude and polarity, but the out-put current to the battery and the electrical circuits remains unidirectional.
1. In each revolution of the magnet, the ………………………… of each phase winding changes, and as a result, the current changes direction.
2. Rectification is a process whereby alternating current (AC) is converted into ………………………… current (DC.)
3. Automotive alternators use ………………………… in the rectifier assembly.
Two methods of connection can be used for the stator or phase windings - Star (or Wye connection); and Delta connec-tion.
In the Star method of connection, 1 end of each phase winding is taken to a central point where they are connected together. This is known as the star or neutral point. The other end of each winding is connected in the bridge rectifier circuit be-tween a positive and a negative diode. Each winding is then always part of a complete circuit.
In the Delta method, the windings are connected in the shape of a triangle. Connections are then taken from each point of the triangle, to the bridge circuit.
1. In the ………………………… method, the windings are connected in the shape of a triangle.
2. Two methods of connection can be used for the stator or phase windings - ………………………… (or Wye connection); and Delta connection.
3. This is known as the star or ………………………… point.
Student/Intern information:
Name Date Class
Handout Activity: HA778
Supervisor/Instructor information:
Name Signature Date
Score / 3
Summary Two methods of connection can be used for the stator. Star or wye connection and delta connection.
Current is provided to the rotor by means of the slip rings and brushes.
When the engine is running, most alternators supply the field current directly by means of three extra diodes connected to the bridge rectifier circuit. Extra diodes are known as field diodes or exciter diodes and the alternator is said to be self-exciting. However, this self-excitation can only occur when the alternator is producing an output.
When the ignition switch is closed, current can flow from the battery positive terminal through the ignition switch and charge indicator lamp to the L terminal of the alternator. The circuit is completed through the slip rings and rotor field wind-ing, and through the voltage regulator to ground on the vehicle frame.
The small amount of current flowing in the circuit illuminates the indicator lamp and provides the initial excitation of the field winding. This magnetizes the rotor pole shoes and pro-duces a weak magnetic field.
When the rotor is driven by the engine crankshaft, the rotating magnetic field induces a voltage in the phase wind-ings which is applied to the B positive alternator output terminal. However, this voltage is also impressed on the exciter diodes and current can now flow directly to the field circuit, restricted only by the resistance of the field winding. This strengthens the magnetic field and the output voltage rises quickly.
The voltage regulator now takes over to control the field circuit current and maintain a pre-set regulated output volt-age at the B-positive terminal voltage of approximately 14 volts. As the voltage on each side of the charge indicator lamp is now equal, there can be no current flow through the lamp and the lamp is extinguished.
The aternator is now said to be charging and since the output voltage at the B-positive alternator terminal is greater than that of the battery, the current flows to the battery to begin the re-charging process.
The alternator output voltage can be controlled or regulated by varying the rotor current.
Student/Intern information:
Name Date Class
Handout Activity: HA779
Summary When the ignition is first switched, current flows through the charge indication lamp, the rotor windings and voltage regulator to ground. Current flow through the rotor winding is controlled by the voltage regulator when the engine is running.
When the engine is running and voltage output is low, the reg-ulator switches the rotor circuit to ground and maximum cur-rent flows through the rotor field winding. The high intensity magnetic field created raises the value of the induced voltage in the stator windings and alternator output rises. The output voltage is also impressed on the exciter diode circuit and the output voltage is sensed by the regulator control circuits via the regulator “L” terminal.
When the maximum allowable voltage has been reached, the control circuits switch the rotor field circuit off and the mag-netic field at the pole shoes reduces in size, or “decays”. The decaying magnetic field reduces the magnitude of the voltage induced in the stator windings and lowers the alternator output voltage. This again is sensed by the voltage regulator control circuits and the rotor circuit is switched on once more.
The regulator switches rapidly between the ‘ON’ and ‘OFF’ conditions, within the pre-set maximum and minimum volt-ages, to allow the alternator to maintain an output voltage of approximately 14 volts and at the same time deliver the current needed for electrical system operation.
1. The regulator switches rapidly between the ‘ON’ and ‘OFF’ conditions, within the pre-set maximum and
minimum voltages, to allow the ………………………… to maintain an output voltage of approximately 14 volts
and at the same time deliver the current needed for electrical system operation.
2. When the maximum allowable ………………………… has been reached, the control circuits switch the rotor field circuit off and the magnetic field at the pole shoes reduces in size, or “decays”.
3. When the engine is running and voltage output is low, the ………………………… switches the rotor circuit to ground and maximum current flows through the rotor field winding.
Student/Intern information:
Name Date Class
Handout Activity: HA780
Summary The regulator switches rapidly between the ‘on’ and ‘off’ conditions, to allow the alternator to maintain an output voltage of approxi-mately 14 volts.
Electronically controlled and electrically driven devices are re-placing mechanically driven components to provide more and more of the functions in an automobile, as well as to extend the range of functions. Demand for stable electrical power has risen and will continue to rise.
As lights and other accessories are turned on and the load on the system increases, the current output to the circuits must be increased and the output voltage must be maintained.
The regulator again adjusts the rotor field circuit, but this time increases the current flow and therefore the magnetic field strength. The induced voltage in the stator rises to maintain system voltage and increase current output. There is no need for a current regulator as the design of the stator winding determines the maximum current output of the alternator at a system operating voltage of 13.8 to 14.2 volts.
If an alternator is rated at 40 amps it is capable of maintaining a system voltage of 13.8 to 14.2 volts up to a current load of 40 amps.
1. The ………………………… again adjusts the rotor field circuit, but this time increases the current flow and therefore the magnetic field strength.
2. The induced voltage in the stator rises to maintain system voltage and increase ………………………… output.
3. As lights and other accessories are turned on and the load on the system increases, the current output to the
circuits must be increased and the output ………………………… must be maintained.
Student/Intern information:
Name Date Class
Handout Activity: HA781
Summary As demand for power increases, the charging system must maintain the system voltage even when under load.
As the number of electrical components increase, vehicles require increasing amounts of available electricity. Vehicles have traditionally used 12-volt batteries and a 14-volt charg-ing system, but to meet the increased demand from such high usage systems as electric drives, higher voltage batteries and packs with an appropriately high voltage charging system are necessary.
The advantages of using higher voltage systems include: more power for systems and accessories, fewer concerns about volt-age drop across the system, and the use of smaller diameter wires for higher power draw, which also reduces the overall weight of the vehicle.
If we apply Ohm’s law we can see how the differences work.
Take, for example, a vehicle with a conventional 14-volt system with a charging current of 200 amps. Using Ohms law, we find that 14 Volts times 200 Amps equals 2800 Watts.
In a higher voltage system, less current is needed to deliver the same amount of power.
By comparison, using Ohms law again, but this time with a 42-volt system, we find that 2800 Watts over 42 Volts equals 66.6 Amps.
For the same amount of “power” the current has decreased by 2 thirds. This means that for any given current flow the cable diameter on a 42-volt system can be reduced in size.
Different types of generation systems can produce this high power output. One method is to combine the vehicle starter motor and charging system into a single unit. A number of “Hybrid” gasoline-electric vehicles use this sys-tem and mount the starter/generator on the flywheel between the engine and transmission.
Student/Intern information:
Name Date Class
Handout Activity: HA782
Summary Vehicles have traditionally used 12-volt batteries and a 14-volt charging system, but to meet the increased demand from such high usage systems as electric drives, higher voltage batteries and packs with an appropriately high voltage charging system are necessary.
