A single wire alternator by design maintains the operating & charging voltage within an acceptable range. Usually 13.6 - 14.8 volts. You can measure this with the engine running ~ 1500-1800 RPM. This however is only one charging test and doesn't prove the condition of the alternator. Actual VS Rated output, AC ripple / diode test and parasitic draw tests also need to be performed in addition to the regulated voltage test.
If you have any concerns about the battery condition the first step is to test it.
Initial Battery Test
Test Battery voltage first. Measure the voltage directly at the battery posts and not the cable terminal ends. Battery should be 12.6 volts minimum. If lower than 12.6 volts the battery is discharged. Voltage above 12.6 volts is a surface charge and is of no consequence. Example: 12.6 VDC = 100% state of charge. 12.3 VDC = 50% state of charge. 12.00 = 0% state of charge. Below 100% then charge and retest. If battery is at 12.6 VDC then proceed to the load test.
Using a Variable Load Tester
Test at 1/2 CCA rating OR 3X the AH rating. Carbon pile load is applied for 15 seconds and voltage is measured while under load. Voltage must be at 10 volts minimum. If the loaded voltage drops rapidly or maintains below 10 Volts THEN a 3 minute battery charge test should be done.
Alternatively a capacitance type battery tester can be used instead of a variable load tester. These use an algorithm to test the battery against its rating and take temperature, capacitance, resistance and loaded, unloaded and recovery voltage into consideration.
3 Minute Battery Test
Attach a high rate charger and set at ~40 amps charge. Monitor battery voltage and measure after 3 minutes of charging. If voltage rises to above 15 volts within three minutes the battery is sulfated and should be replaced. If voltage remains below 15 volts continue charging and monitoring voltage. Discontinue charging when voltage reaches 15 volts.
Final Load Test after charging
Turn off the charger. Measure battery voltage. Repeat the load test if open circuit voltage is @ 12.6 volts minimum.
If you have any concerns about the battery condition the first step is to test it.
Initial Battery Test
Test Battery voltage first. Measure the voltage directly at the battery posts and not the cable terminal ends. Battery should be 12.6 volts minimum. If lower than 12.6 volts the battery is discharged. Voltage above 12.6 volts is a surface charge and is of no consequence. Example: 12.6 VDC = 100% state of charge. 12.3 VDC = 50% state of charge. 12.00 = 0% state of charge. Below 100% then charge and retest. If battery is at 12.6 VDC then proceed to the load test.
Using a Variable Load Tester
Test at 1/2 CCA rating OR 3X the AH rating. Carbon pile load is applied for 15 seconds and voltage is measured while under load. Voltage must be at 10 volts minimum. If the loaded voltage drops rapidly or maintains below 10 Volts THEN a 3 minute battery charge test should be done.
Alternatively a capacitance type battery tester can be used instead of a variable load tester. These use an algorithm to test the battery against its rating and take temperature, capacitance, resistance and loaded, unloaded and recovery voltage into consideration.
3 Minute Battery Test
Attach a high rate charger and set at ~40 amps charge. Monitor battery voltage and measure after 3 minutes of charging. If voltage rises to above 15 volts within three minutes the battery is sulfated and should be replaced. If voltage remains below 15 volts continue charging and monitoring voltage. Discontinue charging when voltage reaches 15 volts.
Final Load Test after charging
Turn off the charger. Measure battery voltage. Repeat the load test if open circuit voltage is @ 12.6 volts minimum.
