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Mysterious electrical shutdown...


Stuart

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Our CTLS has just come back from hard landing repair, annual and rubber hose replacement. Yes, we did it all at once since the engine was going to be off the plane anyway.

 

Just before the accident that caused all this work (end of September) one of our club members reported all the electrical systems "shut down". This happened while taxiing to the runway for takeoff. According to the pilot, all avionics, interior and exterior lights all shut off. The engine was still running so he taxied back to the hanger. There were no abnormal readings or alarms prior to the failure. The next day all powered up and worked as expected.

 

A day or two later the plane had a hard landing that took it out of service for three months. While down I had the A&P replace the 5 year old battery and generator breakers thinking one of them could be going bad and causing the electrical failure.

 

The aircraft was put back into service last Sunday. I flew for an hour without trouble. One day later, the same pilot who had experienced electrical failure last time had it happen again. This time while warming the engine in front of our hanger.

 

He reports that the engine continued to run so he spent some time cycling breakers with no effect. When he shut down the engine to "start from scratch" he says the engine wouldn't even turn over. No cranking.

 

After an overnight battery charge, all seems to be working again. There have never been alarms or abnormal readings on the EMS. We're looking for where to start to identify this problem. Any ideas?

 

Stuart Rauh

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I would look at the person who keeps having the problem. They may be unintentionally overloading the system if you still have the old style landing light and they are running everything at startup. The alternator at idle cannot fully drive everything, and it will draw from the battery until no power is left.

 

Are they also plugging things into the power port? An ipad charger is 10 watts, so at 12 volts, it draws almost an amp.

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Stuart,

 

I have had 2 similar occurrences. My CTSW has toggle master switches and on occasion I will inadvertently turn off the alternator when I retract flaps. A ways into the flight everything turns off, they engine still runs and my 496 works on its battery. At this point, 12,500' over big mountains I realize the alternator is turned off at the master and I switch it back and all becomes normal. This deep cycling is a battery killer.

 

Perhaps your club member is failing to open both circuits and is running on battery as long as it lasts?

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My CTsw has two master switch/breakers ("BAT" and "GEN" if I remember correctly). If I close BAT (completing the circuit), it will energize the electrical system but not the alternator (i.e., plane has battery power only). The plane will start and fly with all the avionics and other electrical systems operating on battery power. The one time I started and flew the airplane in that configuration, I has "all the electrical systems shutdown" when the battery went flat in flight. When the alternator breaker (GEN) was then closed (completing the circuit), the airplane then also charged the battery. Better that way.

 

This is exactly the same as the scenario described by CT, above, and is consistent with the report of your pilot.

 

Just a report of my experience, not an assessment of your airplane or pilot.

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My CTsw has two master switch/breakers ("BAT" and "GEN" if I remember correctly). If I close BAT (completing the circuit), it will energize the electrical system but not the alternator (i.e., plane has battery power only). The plane will start and fly with all the avionics and other electrical systems operating on battery power. The one time I started and flew the airplane in that configuration, I has "all the electrical systems shutdown" when the battery went flat in flight. When the alternator breaker (GEN) was then closed (completing the circuit), the airplane then also charged the battery. Better that way.

 

This is exactly the same as the scenario described by CT, above, and is consistent with the report of your pilot.

 

Just a report of my experience, not an assessment of your airplane or pilot.

 

Fred,

 

The alternator may be failing for another reason otherwise the pilot is likely failing to close the GEN breaker, it fits.

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I still think you need to check the person who is having the problem. It occurred on the ground both times, and that is the only person experiencing the problem.

 

Also, lead-acid batteries draw a SIGNIFICANT amount of power if they are discharged (doesn't take long when cranking a 912 engine). That, topped with running everything else, might overload the alternator. I do not know how ducati regulators manage over-current conditions, but it's worth examining.

 

I had this happen to me at Urbana Grimes field. I noticed that system voltage was dropping during taxi, and switching the alternator breaker on and off wasn't helping. But, after shutting down and charging the battery for a while, the problem did not come back. At the time, I recall having all electronics and lights on, and my iPad plugged in. I've since refrained from switching everything on until I've got system voltage showing correctly, and monitoring as things are switched on.

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Maybe check the back of the ignition/start key switch on the lower center panel. You'll be able to see where two wires are attached to the switch via the same connector. If one or both of the wires are not making good contact, intermittent electrical problems will occur.

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