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CHAPTER Charging Systems 7 Instructor Name: (Your Name)

Learning Objectives Explain how an alternator produces a regulated DC voltage Describe how electrical contact is made through the rotating rotor windings Trace the current flow from the stator winding through a rectifier bridge Explains haw a voltage regulator controls the strength of the rotors magnetic field

Learning Objectives (continued)
Define the purpose of the diode trio or the field diode assembly Perform a preliminary inspection of a charging system Disassemble and inspect the internal components of a typical alternator Test a truck charging system Perform a parasitic current draw test

Alternators Role in the Electrical System
Recharges the trucks batteries Primary power source when the truck is running Produces AC voltage and converts it to DC with diodes Regulates the voltage supplied to the system and the battery

Cutting Magnetic Lines of Force with a Conductor to Produce a Positive Voltage
Figure 7-1 Cutting magnetic lines of force with a conductor to induce a voltage: conductor is moving from right to left through the magnetic field.

Cutting Magnetic Lines of Force with a Conductor to Produce a Negative Voltage
Figure 7-2 Conductor has been moved from left to right through the magnetic field causing a reversal of polarity of induced voltage.

Inducing More Voltage The greater the number of magnetic lines of force that are cut by a conductor per second, the greater the voltage that is induced in the conductor Increase the speed of the conductor that moves through the magnetic field Increase the strength of the magnetic field

Voltage Waveforms An oscilloscope displays voltage amplitude on the y-axis and the time on the x-axis The oscilloscope can be adjusted to change the values of each division of both the horizontal and vertical axis 120 VAC from a wall socket would form a sine wave on the oscilloscope The sine wave would alternate between positive and negative This alternating polarity is where the term alternating current came from

Voltage Waveforms (continued)
The number of times a wave form repeats per seconds is called frequency and is measured in hertz

Simple Alternator Figure 7-8 Simple alternator.

Single Loop Rotating Through a Magnetic Field
Figure 7-9 Single loop rotating in magnetic field at six different positions.

Voltage Wave Form Figure 7-10 Voltage waveform produced by a single loop rotating in a magnetic field.

Magnets Rotating Inside a Conductive Loop
Figure 7-11 Magnet rotating inside of conductive loop induces an AC voltage in the loop.

Magnetic Field Lines of Force Flow Through a Stator
Figure 7-12 Magnetic field lines of force flow through stator.

Electromagnet Rotating Inside Conductive Loop
Figure 7-13 Electromagnet rotating inside of conductive loop induces an AC voltage in the loop.

Sine Wave Produced by Magnet Rotating Inside Conductive Loop
Figure 7-14 Sinusoidal AC voltage waveform produced by rotating electromagnet inside of a conductive loop.

Three-Phase Power Three-phase alternators have three conductive loops
Each loop is place 120° apart (360°÷3=120°) Each loop will form a single sine wave voltage form with every revolution of the rotor

Three Conductor Stator and Output Sine Wave
Figure 7-16 Three conductive loops connected together and spaced around the stator.

Three-Phase Sine Waveform Voltage Trace
Figure 7-17 Three-phase sine waveform voltage trace.

Delta and Wye Wound Stators
Figure 7-20 Stator winding arrangements.

Rotor Components Figure 7-21 Rotor components consist of coil and pole pieces installed on rotor shaft.

Alternating North and South Poles of Rotor and Magnetic Field Between Them
Figure 7-22 Alternating north and south poles of rotor pieces produce a rotating magnetic field. Figure 7-23 Magnetic fields between adjacent rotor pole pieces surround the rotor.

Three-Phase Stator Winding
Figure 7-24 Three-phase stator windings installed in laminated iron frame.

Converting AC to DC AC current from alternator must be converted to DC current Diodes, often called rectifiers, convert AC current to DC current The output of the alternator stator windings is connected to a four diode bridge rectifier

Four Diode Bridge Rectifier
Figure 7-27 Single-phase AC rectifier bridge.

Full Wave Rectification
Figure 7-28 Full wave rectification reverses the polarity of the negative portion of a sine waveform.

Three-Phase Rectifier Requiring Six Diodes
Figure 7-30 Three-phase rectifier requires six diodes.

Rectified Three-Phase Voltage
Figure 7-31 Rectified three-phase voltage.

Voltage Regulation Fundamentals
Modern truck alternators are designed to maintain a 14.2V output for a 12V system Voltage regulators maintain alternator output by controlling the current flow through the rotor field coil windings If the alternator output is low, current to the rotor field coil is increased If the alternator output is high, current to the rotor field coil is decreased

Switch Controlling Current Flow
Figure 7-36 Switch shown as controlling current through rotor field coil through slip rings and brushes.

Voltage Regulation Fundamentals (continued)
Modern truck voltage regulators use pulse width modulation to control current flow to the rotor field coil Pulse width refers to the on portion of a pulse compared to the off portion of a pulse The longer the on portion a pulse has the more current supplied to the rotor field coil The shorter the on portion a pulse has the less current supplied to the rotor field coil Voltage for the rotor field coil is supplied by the diode trio or a field diode

Pulse Width Modulation Duty Cycle
Figure 7-37 (A) Lights on for one time period and off for two time periods resulting in dim lamp output. (B) Lights on for two time periods and off for one time period resulting in brighter lamp output. Figure 7-38 Pulse width modulation (PWM). Duty cycle is the percentage of on-time per cycle.

Alternator Terminals and Circuits
Positive Output Terminal – insulated terminal marked BAT or B+. Normally connected to battery terminal of started and battery positive Ground Terminal – Most truck alternators have a ground terminal that connects to the starter ground or frame. Some alternators ground through the alternator mounting bolts Relay Terminal – Marked R or AC. Used on some systems to power relay only when engine is running

Alternator Terminals and Circuits (continued)
Indicator Light Terminal – Available on some alternators. Dash indicator will light if alternator in not functioning. Remote Sensing Terminal – Provides an indication of the battery voltage to the voltage regulator

Brushless Alternator Figure 7-42 Brushless alternator rotor and field coil.

Charging System Problems
Complaints of High Charging Voltage Complaints of Low Charging Voltage Voltmeter reads high Sulfur smell Wet batteries and high water usage Lamps that are too bright and burn out quickly, turn signals that flash too rapidly Decreased battery life Voltmeter reads too low Slow cranking speed or no crank Lamps that are too dim and turn signals that flash too slowly Decreased battery life

Tech Tip Testing a charging system using batteries that are not fully charged may lead you to an incorrect diagnosis. Recharging batteries can take a considerable amount of time. Having sufficiently charged batteries that you can temporarily install for testing can save you and your customer valuable time.

Delco Remy 28SI Alternator
Figure 7-46 Delco Remy 28SI pad-mount alternator with serpentine drive belt and automatic tensioner.

CAUTION Each OEM has procedures for testing the charging system that should always be followed. Procedures listed are only examples and can not be performed on all vehicles.

Testing Alternator Charging Circuit Voltage Drop
Figure 7-47 Testing alternator charging circuit voltage drop using carbon pile load tester, engine off.

Determining Individual Alternator Cable Voltage Drops
Figure 7-48 Determining individual alternator cable voltage drops, engine off.

Connect voltmeter across the alternator output positive and negative leads. Connect ammeter probe to alternator output lead. Start engine, run at 1500 rpm for 2 minutes. Observe voltage and current reading with all electrical loads off and engine running. Conduct next test based on the results of test and chart below: Figure 7-49 Determining individual alternator cable voltage drops.

Test 1, Acceptable Unloaded Charging Voltage
Connect ammeter current probe to output lead of alternator Connect carbon pile load tester across the battery terminal Start engine, run at 1500 rpm, turn off all loads Run 2 minutes with no electrical load Adjust carbon pile until ammeter reads highest value. Quickly return carbon pile to the unloaded position.

Test 2, Low Alternator Output Voltage
Rotor lost residual magnetism. “Flashing the Field” may be required to start alternator charging. Voltage regulator may be set too low Full field the alternator to determine if the voltage regulator is faulty or if the alternator is faulty

WARNING Only perform a full field test if specified by the OEM. Use extreme caution when full fielding an alternator. The output voltage can rise to a very high level in a brief time and cause damage to the electrical system. It may also be very difficult to access the full fielding access hole on some alternators. Be careful when working around rotating components to avoid injury.

Test 3, High Charging Voltage
Possible faulty voltage regulator Internal short to ground in the field coil Voltage regulator set too high Check OEM information for specific test for high charging voltage

CAUTION Never disconnect any battery or alternator cable when the engine is running. The rapid change in alternator output current can result in a very high alternator output voltage, which can destroy modern truck electronics. Never operate an engine without the batteries connected in parallel with the alternator output. This battery-less operation will cause the alternator output voltage to become very unstable, which could result in damage to electronic components.

Parasitic Draw Test Turn off all electrical loads on truck.
Connect current ammeter probe on negative lead of battery. All other batteries may need to be disconnected. Watch as the various modules power down. After a couple of minutes observe parasitic load current. Using circuit diagram as a guide remove circuit protection devices one at a time until the parasitic load on ammeter drops off.

Testing Rotor With an Ohm Meter
Figure 7-52 Testing for rotor field winding resistance. Figure 7-53 Testing for a short to ground field winding.

Testing Stator with an Ohmmeter
Figure 7-54 Testing the stator for open circuits. Figure 7-55 Testing the stator for shorts to ground.

Testing The Rectifier with an Ohmmeter
Figure 7-56 Testing the rectifier diodes.

Testing Diode Trio with an Ohmmeter
Figure 7-57 Testing the field diode or diode trio.

Simplified Regulator Circuit
Figure 7-58 Simplified electronic voltage regulator schematic – zener diode D2 is the primary component.

Summary The charging system supplies the energy to recharge the truck batteries. The alternator produces a three-phase alternating current through the principles of electromagnetic induction. The alternating current is rectified to direct current. The rotor is an electromagnet that produces a rotating magnetic field inside of the stationary windings called the stator. The magnetic lines of force produced by the rotor cut through the stator winding to induce a sine wave voltage in the stator windings.

Summary (continued) The three-phase stator winding may be connected in a delta or wye (y) configuration. Either configuration produces a three-phase alternating current wave form. The means of making electrical contact with the rotor field windings is through slip rings and brushes. The alternator output voltage is controlled by regulating the current flow through the rotor field windings. The voltage regulator uses PWM to control the field winding current level.

Summary (continued) The rectifier uses a series of diodes to transform the negative half of the sine wave into a positive wave form. The pulsating positive polarity wave form is smoothed by a capacitor. The small amount of pulsation that remains in the wave form is called ripple voltage. Testing the charging system includes testing the batteries, making a visual inspection, and measuring charging system circuit resistance. Circuit resistance testing is performed by measuring the voltage dropped on the charging circuit at rated alternator current flow in the circuit.

Summary (continued) Parasitic current draw is the key-off current draw of the trucks electrical system. Parasitic current is measured with an ammeter. The source of the current draw can be determined by removing fuses one by one.