Alternator Diode (Rectifier)

A typical rectifier uses several diodes arranged in a bridge. A failed diode can reduce charging output and cause a whining noise in the audio system. A leaking diode can drain the battery while the car is parked. An oscilloscope shows a failed diode as a missing hump in the charging ripple pattern, and many battery testers report excessive ripple. On many alternators the rectifier can be replaced separately, but complete exchange alternators are often the practical choice.

Diodes let current flow in one direction only, so the alternating output of the stator windings is turned into a steady charging current.

Never disconnect the battery with the engine running, as voltage spikes can damage the diodes. Reversed jump-start leads can destroy the rectifier instantly.