Runaway Generator ROTAX 912ULS

Bob

1. Make sure the Electrical Installation is according to latest rev of Rotax 912ULS Install manual. Including 22.000uF capacitor.

2. I would test the voltage regulator and the capacitor.

Is the capacitor added as part of a Service Bulletin? Thanks, Bob

I dont know if there is a SB. But for sure, this capacitor is in the Rotax 912ULS install manual, as well as in the VANs RV12 electrical circuit.

Bob,

If the battery is disconnected while the alternator is in operation the voltage can spike. Is it possible the master solenoid failed?  Or the wiring or switch that controls it?  

Is the 30 amp breaker you are speaking of protecting the circuit which connects the alternator to the airframe electrical bus or the battery to the electrical bus? In other words, does opening this breaker disconnect the alternator from the airframe bus? Assuming yes, did the airframe power bus go dead when you opened this breaker or did it stay powered by the battery?  

Hi all

The installation manual is very clear.  If you lose, or disconnect, the battery power while the engine is running and do NOT have a capacitor then the regulator will fail internally.  The capacitor has 2 main functions.  First to stabilize the wave coming out from the regulator and second to allow the power a place to absorb the output in the event you have to drop the battery offline.  This will maintain your instruments and other things you want to work while operating without a battery or in a battery fail mode.  it should stop regulator failure from loss of a battery.  

Cheers