Charging System Testing and Service Unit 5 Charging System Testing and Service

Introduction Almost every system relies on: Automobiles have: 12-volt storage battery Electrical and electronic components Engine starting system Electrical charging system Electronic control modules Networking systems

Charging Systems—Charging Systems Output Test (1 of 4) Charging systems are voltage regulated. Alternator maintains a set voltage. Voltage drops as electrical load current increases. Voltage regulator increases current output. Increases system voltage

Charging Systems—Charging Systems Output Test (2 of 4) Start alternator output tests with voltmeter testing of regulated voltage. Voltage at which regulator allows alternator to create only a small charge Should be between specified minimum and maximum regulated voltage

Charging Systems—Charging Systems Output Test (3 of 4) Then check charging system output. External electrical load to reduce battery voltage Tricks regulator into making alternator produce maximum amperage output Read by inductive ammeter If within 10% of rate output, still okay

Charging Systems—Charging Systems Output Test (4 of 4) If less than 10%, indicates: Faulty regulator Faulty alternator Excessive voltage drops on alternator output or ground circuits

Charging Systems—Testing Charging System Circuit Voltage Drop (1 of 6) Excessive voltage drop may cause: Battery not fully charged—reduced voltage to battery Battery charged but alternator at higher voltage—may overheat

Charging Systems—Testing Charging System Circuit Voltage Drop (2 of 6) Problem shown by where voltage is sensed. Alternator—battery undercharged Battery—Alternator at higher voltage External alternator output circuit has: Wires and fuse or fusible links Ground wire back to battery

Charging Systems—Testing Charging System Circuit Voltage Drop (3 of 6) Voltage drop may occur in: Output current circuit Ground circuit Terminals and connectors (most common) Small amount of resistance can cause significant voltage drop.

Charging Systems—Testing Charging System Circuit Voltage Drop (4 of 6) Voltmeter or DVOM measures voltage drops on all circuit parts. Voltmeter with min/max range setting: Records and holds maximum voltage drop occurring in particular operation cycle Only works when circuit under load, current flow Always perform test with circuit on.

Charging Systems—Testing Charging System Circuit Voltage Drop (5 of 6) To measure with DVOM: Most efficient to first measure voltage drop on both entire positive and negative sides Connected in parallel across the: Component Then narrow down to individual components Cable Connections

Charging Systems—Testing Charging System Circuit Voltage Drop (6 of 6) Example: Connect black probe to alternator’s output side. Connect red probe to positive post of battery. Operate charging system under heavy load. Record voltage drop across output side. Perform same test on ground side.

Charging Systems—Replacing an Alternator (1 of 3) Electrical faults: Worn and noisy bearings No-charge Other internal or external mechanical damage Undercharge Overcharge Mechanical faults:

Charging Systems—Replacing an Alternator (2 of 3) Take precautions when changing alternator. Battery voltage present at output terminal Disconnect at least one battery terminal from battery. Do not operate alternator with battery or terminals at back of alternator disconnected.

Charging Systems—Replacing an Alternator (3 of 3) Usually between 31.8 and 14.5 volts. If not: Alternator Internal or external voltage regulator Drive belt loose Built-in voltage regulating circuit in ECM/BCM Drops in charging or voltage sensing circuit If not the problem, check for faulty:

Charging Systems—Diagnosing Undercharge and Overcharge (1 of 5) Undercharging Overcharging Electrical system not fully functional Short life for electrical component Battery not fully charging Overcharges battery Increases gassing and water loss Sulfation and early battery death

Charging Systems—Diagnosing Undercharge and Overcharge (2 of 5) Voltage regulator maintains constant voltage output from alternator to max output current. Always check specs for regulated voltages. In non-PCM–controlled 12-volt charging system: Regulated alternator output voltage If outside specs, further testing needed

Charging Systems—Diagnosing Undercharge and Overcharge (3 of 5) If overcharging: Faulty regulator Worn brushes Voltage regulator High resistance in rotor Regulator ground Open/shorted diode Open/shorted stator windings Shorted cell on battery If undercharging: Loose drive belt

Charging Systems—Diagnosing Undercharge and Overcharge (4 of 5) Check easiest and most common faults first. Drive belts slipping Shorted battery cell Inadequate battery capacity

Charging Systems—Diagnosing Undercharge and Overcharge (5 of 5) Test voltage drops on output and ground circuit if voltage output is low. If none found, fault is inside alternator. Faulty regulator Worn brushes Faulty rotor

Summary The first item that should be checked if an alternator is not charging according to the manufacturer’s specifications is the belt tension and condition. Charging system voltage matching specification under load is the critical factor. Before determining alternator failure, verify all inputs and connections, including alternator ground.

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