0
Nov, 29, 2023Introduction
Alternator Testing Procedure
Details
Step 1: Visual Inspection & Initial Voltage Check
Inspect all external wiring connections for:
1. Open circuits
2. Incorrect wiring
3. Short circuits
Measure voltage at B+ terminal using a multimeter:
Expected value: Battery voltage (~12.6V for 12V systems / ~25.2V for 24V systems)
Step 2: Ignition-On Test
Turn ignition key to "ON" position (without starting engine)
Measure voltage at D+ terminal:
Healthy system: ~0.5-2V lower than battery voltage
Verify charge indicator light illumination:
Should glow brightly (indicates excitation circuit intact)
Step 3: Running Voltage Test
Start engine and measure B+ voltage at 2000 RPM:
Normal output: 13.8-14.8V (12V) / 27.6-29.6V (24V)
If no output: Proceed to Field Flash Test
Field Flash Test (For No-Output Condition)
Connect a 2.5mm² wire from battery positive (+) to D+
Briefly touch wire to D+ (<1 second) while engine runs
Recheck B+ voltage:
If voltage restored:
✓ Re-test Steps 3-5
✓ Diagnose open circuit in:
• Charge indicator bulb
• Instrument cluster connector
• Wiring harness
If no voltage:
✓ Confirmed alternator failure (replace unit)
Step 4: Partial Load Test
Activate headlights
Verify B+ voltage remains within spec
Step 5: Full Load Test
Engage major loads (A/C + headlights + wipers)
Confirm voltage regulation:
Minimum allowable: 13.2V (12V) / 26.4V (24V)
Diagnostic Notes:
Always prioritize safety: Disconnect battery before wiring checks
For modern smart alternators, consult manufacturer specs for excitation requirements
Voltage drop >0.5V across B+ cable indicates wiring/connection issues
