Alternator
| Measurement: | Harmonic content of the charge voltage when the engine is idling. |
|---|---|
| Check Objective: | Check the charging operation and the excitation and rectification diodes of the alternator. |
Preparation
Switch off the engine and ignition. Ensure the connections on the alternator, starter and battery are seated correctly. Check the alternator belt tensioning.
Connections
| INPUT A | COM/TRIGGER |
|---|---|
| Connect the red measurement lead to the B+ or D+ (terminal 61) on the alternator (the battery can also be temporarily connected). Ensure correct polarity! |
Procedure
Start the engine and allow it to idle. If the battery has been connected, switch on the electrical loads (e.g., headlamps, heated rear screen) and increase the engine speed.
Reference Curve
The appearance of the measurement curve can vary according to the operating condition (load, battery charge, engine speed). As a result, the following fault diagrams can simply be used as a reference for the evaluation process. However the deviations resulting from faults are generally so large that it should be possible to clearly identify the fault itself.
Fault Scheme 1
Symptoms:
One harmonic wave is missing
| Possible Causes | Countermeasures |
|---|---|
| Faulty excitation diode (open-circuit) | Repair or replace alternator. |
Fault Scheme 2
Symptoms:
Wide disruption in the plotted curve and heavily distorted harmonic wave.
| Possible Causes | Countermeasures |
|---|---|
| Faulty excitation diode (short-circuit) | Repair or replace alternator. |
Fault Scheme 3
Symptoms:
Plotted curve contains positive voltage spikes
| Possible Causes | Countermeasures |
|---|---|
| Faulty positive rectification diode (open-circuit) | Repair or replace alternator. |
Fault Scheme 4
Symptoms:
Only two half-waves visible
| Possible Causes | Countermeasures |
|---|---|
| Faulty positive rectification diode (short-circuit) | Repair or replace alternator. |
Fault Scheme 5
Symptoms:
Very narrow interruption in the plotted curve
| Possible Causes | Countermeasures |
|---|---|
| Faulty negative rectification diode (open-circuit) | Repair or replace alternator. |
Fault Scheme 6
Symptoms:
Broad interruption in the plotted curve (only two phases visible)
| Possible Causes | Countermeasures |
|---|---|
| Faulty negative rectification diode (short-circuit) | Repair or replace alternator. |
Fault Scheme 7
Symptoms:
Negative spikes after each harmonic
| Possible Causes | Countermeasures |
|---|---|
| Open-circuit of one phase or two phases short-circuited together | Repair or replace alternator. |