04-20-2004 Ask Mike! Archive
Self exciting alternators

The Beechcraft Duchess has self exciting alternators for it's O-360-A1G6D engines. For normal operations the field current is generated by current from the battery. When the battery is inop and say you were to hand start the engines, would the alternators generate their own field current with an internal dc generator or are the alternators unable to self excite?

Peter


Peter;

It's been over ten years since I've had a Duchess in the shop, so after reviewing the "Alternator self-exciting check" text in the Duchess 76 Maintenance Manual, Chapter 24-30-00, page 9, I would say I believe so. I don't have a copy of the POH for the 76; you would most likely find the definitive answer in the emergency procedures section.

I would not recommend hand starting these engines. Anytime an engine is hand started, unless the people (inside AND outside the aircraft) doing it are properly trained, could be a recipe for disaster. In this instance, after one is started, it would take a while to sufficiently charge the battery to start the other. Couple this with the fact the right engine on the 76 turns left might cause confusion to the person outside; you also have the nose of the airplane eliminating working (and egress) room, one engine running so communication is hampered....

Please charge the battery or get an APU start.

Gear Green,
Mike