Within the last ~250 hours I've had two alternator shear couplings fail on my RV-6. The first failed after ~248 hours of flying, the second failed at less than two. The alternator is a Plane Power FS1-14B (30A, internally regulated, bolted to the accessory pad) and the airplane is wired using Bob Nuckoll's Z-11 diagram in the Aero Electric connection. This is the only alternator on the plane.
The airplane is a full-up Dynon system (10" Skyview, ADS-B, transponder, wx rcvr), a Garmin GTR200 radio, landing light, strobes, nav light. None of the lights were turned on between repairing the first failure and the second one.
The going failure theory is an intermittent connection in the field circuit that induces a heavy alternator load by turning it on and off but there isn't anything in the 1Hz data traces from the Dynon that indicates this is the case. Nor is there evidence of any loose connections or nicked wires in the field circuit.
The image shows the volt and amp trace for the last 1.7 hour flight. The failure occurred around count #6184. The noise on the front end is startup and taxi. The blip around 2291 was plugging in an iPad.
Any ideas on the failure mode?
The airplane is a full-up Dynon system (10" Skyview, ADS-B, transponder, wx rcvr), a Garmin GTR200 radio, landing light, strobes, nav light. None of the lights were turned on between repairing the first failure and the second one.
The going failure theory is an intermittent connection in the field circuit that induces a heavy alternator load by turning it on and off but there isn't anything in the 1Hz data traces from the Dynon that indicates this is the case. Nor is there evidence of any loose connections or nicked wires in the field circuit.
The image shows the volt and amp trace for the last 1.7 hour flight. The failure occurred around count #6184. The noise on the front end is startup and taxi. The blip around 2291 was plugging in an iPad.
Any ideas on the failure mode?
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