Trouble in the vehicle charging system generally appears through one of two major symptoms: the battery becomes low in charge or the charging rate becomes excessively high. Proper diagnosis requires identifying the symptom and then testing the generator, regulator and electrical circuits to determine the cause.
The generating system includes the generator, voltage regulator, wiring circuits and battery. A fault in any of these components can affect charging performance.
Battery Low in Charge
When the battery is low in charge, several symptoms may appear including slow engine cranking, difficult starting and dim headlights when the engine is idling.
Possible causes include:
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Generator belt worn, loose or slipping on the generator pulley
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Battery in poor condition and unable to hold a charge
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Generator not producing its rated output
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Voltage regulator out of adjustment
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Excessive resistance in the generator-to-battery circuit or battery ground circuit
The first step is to check the battery state of charge and inspect the generator belt for proper condition and tension. If the belt is badly worn or loose, it should be replaced or adjusted before further testing.
Recharge or Replace Battery
Perform a battery capacity test to determine whether the battery is capable of holding a charge.
If the battery fails the capacity test, it should be replaced. If the battery capacity is normal, the charging system should be tested to determine whether the generator and regulator are functioning correctly.
Test Generator Output
The generator output should be tested to determine whether the generator is operating within specifications.
If the generator output equals or exceeds the rated capacity, the next step is to perform a generator regulator test to check regulator operation.
Battery Low in Charge – Generator Output Low
If the generator output is below specifications, a simple grounding test can help determine whether the problem is caused by poor grounding.
Connect a heavy jumper wire from the battery ground post to the generator ground terminal, then repeat the generator output test.
If generator output increases to the rated value after the jumper wire is installed, the problem is likely due to poor grounding between the generator and the engine frame.
In this case:
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Inspect and replace the battery ground cable if it is corroded or damaged
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Clean all cable connections at the battery and engine
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Tighten the generator and mounting bracket bolts
If generator output remains low even after proper grounding, the generator itself may be faulty.
Possible internal generator faults include:
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Open or short circuit in the field windings
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Armature defects
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Worn brushes
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Brushes too short or sticking in the brush holders
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Poor brush contact with the commutator
A generator output test should then be performed to determine the exact component causing the problem.
Battery Low in Charge – Generator Output Normal
If generator output is normal but the battery remains undercharged, the problem may lie with the voltage regulator or circuit resistance.
Test Generator Regulator
Test the voltage regulator to determine whether it is correctly adjusted.
After checking all three regulator units, adjust or replace the regulator as required. If the regulator is operating correctly, the electrical circuit resistance should be tested.
Test Circuit Resistance
Check the external charging circuit for excessive resistance.
If the voltage drop in the circuit is within the specified limits, circuit resistance is considered normal.
If the voltage drop exceeds specifications, excessive resistance exists in the circuit and the faulty component should be located using an external circuit resistance test. Repair or replace the defective wiring or connection.
Other conditions that may cause a battery to remain low in charge include:
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Excessive night driving
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Heavy use of electrical accessories
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Short trips that do not allow sufficient charging time
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Accidental battery discharge
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Incorrect engine lubricant for the ambient temperature conditions
High Charging Rate
An excessively high charging rate can cause electrical component damage and battery overcharging.
Common symptoms include:
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Generator, lights, fuses or radio tubes burning out repeatedly
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Battery requiring frequent refilling of electrolyte
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Ignition contact points burning prematurely
If the generator itself burns out in addition to high voltage conditions, an incorrect setting of the current limiter in the voltage regulator may be responsible.
To determine the cause of high charging rate:
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Ensure all electrical connections, including the voltage regulator ground, are clean and tight.
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Check the voltage regulator adjustment. If voltage regulation is too high, inspect the regulator contacts and replace the regulator if the contacts are burned or damaged.
Correct regulation will prevent excessive generator output and maintain proper charging system operation.
Safety, Copyright and Source Notice
Safety Disclaimer
Working on motor vehicles involves mechanical, electrical and chemical hazards. Always ensure the vehicle is safely supported, the engine is switched off when appropriate, and suitable safety equipment such as gloves and eye protection are used. If you are unsure about any repair or maintenance procedure, consult a qualified mechanic before attempting the work.
Source
Information compiled from period factory service literature.
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