A rectifier is an assembly of diodes that allows current in one direction only. There will be two or three AC terminals and two DC terminals. Within the rectifier, there are two diodes from each AC terminal—one to each DC terminal—that allow a flow of charge toward the positive or away from the negative to create a DC output in the correct direction.
Use a multimeter to test each diode. First, shut down the turbine and disconnect the battery—be sure to wait until the turbine is braked. Next, disconnect all of the wires from the rectifier, taking care to identify them clearly for reconnection. Set the multimeter to the diode test position, usually marked with a diode symbol.
Touching the meter probes to each end of a diode will give three possible readings:
- Open circuit (usually indicated by a digit 1 on the left-hand side of the display, or the letters OL)
- Diode forward voltage (usually a number around 500 mV)
- Short-circuit (usually 0.0)
A properly functioning diode will give an asymmetrical outcome—open circuit one way and a forward voltage the other way. A short-circuit or an open circuit in both directions indicate a bad diode.
Place the red probe on the positive DC terminal and check with the black probe on each of the AC terminals in turn. You should see open circuit (top right photo). Now try reversing the probes and place black on the positive DC. You should get a number on the display each time you touch the red probe to an AC terminal. Check the negative DC terminal in the same way and you should see the exact opposite (bottom right photo).
If you find a shorted diode or one that is open in both directions, the rectifier needs to be replaced. Consider possible causes, including overcurrent, overheating from poor connections, and lightning surges. Replacing your rectifier with one that is made for higher voltage and current may prevent similar problems from occurring in the future.