How Many Volts Should My Alternator Put Out. For others its normal to see as high as 16 volts for long stretches. If the voltage does not change when the engine is started if it does not get above 13 volts or if it charges above 15 volts then the alternator may be faulty.
Stress test the alternator - Place a load on the alternator by turning on the headlights the radio and the air conditioning. Generally 1200 rpms 10amps 1500rpms 20 amps and 2000rpms 35 amps max output is reached at 4500 rpms 51 amps. A voltage regulator helps regulate the voltage that an alternator provides.
The alternator should be tested with the engine idling and electrical accessories such as the radio and headlights turned off.
If its still showing in the 12s its time to replace the alternator. When the engine is running the alternator will typically put out between 138 to 148 volts. A car alternator needs to be putting out at least 13-14 volts ideally between 138 and 142 volts to effectively charge a 12 volt car battery. You now can test the voltage between the terminals of the stator coil at 3000 rpm.
