What is an alternator ripple?
Then, what is acceptable alternator ripple?
A multimeter can read AC voltage and can be used to test for ripple. The alternator should be replaced if AC voltage of more than 50mV is detected (in some cars as much as 100mV is acceptable). If there is more than 0.1 volt (50-100mV, depending on the vehicle) of AC ripple, then the alternator is most likely bad.
Likewise, what causes excessive ripple in an alternator?
Excessive ripple may mean that one winding of the alternator is open or that a rectifier has gone bad. In any event, if the diagnosis is correct, you're probably looking at a new alternator.
Alternator AC ripple – without ECM control. The purpose of this test is to check the rectification of the alternator output voltage, where the alternator output is not regulated by the Engine Control Module (ECM).