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Touring Motor Gliders Association (TMGA)

Main switch and charge fail light

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Jim Lee

Ok, file this one under you learn something new everyday.  I was taxiing out to fly when all hell broke loose with the charging system.  Dynon lady (Nora) yelling at me, lights flickering, electrical power loss then resume, radio off and on, etc.  Huge static noises from the radio, so shut down all equipment to not cause further damage.  Engine was running fine.  Needless to say, did not fly.

I thought it was a battery or battery connection problem.  Looked at the batteries, charged them up, looked at all power connections, everything was fine.  Looked at power connections under the hood, everything was fine.  Without running the engine, on either battery, the charge fail light would flicker and die.  No power to the panel.  Then would get an intermittent power to the panel.  Switch batteries, same thing, flickering, intermittent and then no power at all.  Sometimes I would switch batteries, and power would come on, charge fail light would be on bright.  But while wearing headset with intercom turned on, huge static and hum.  Something was amiss and I was stumped.

Pulled the left panel with the Dynon, and inspected everything behind the panel.  All looked good.  But with some power to the panel, while jiggling the main switch, huge static over the headset, and intermittent power.  Ah ha!  Found a comparable switch at Ace hardware.  Ace stands for aircraft certified equipment.  Installed the new switch, had solid power, thought everything was good.  The next day, started the engine and had a loud hum over the radio and intercom.  Shut down the radio, still had a hum on the intercom over the headset.  Darn it.  Engine was running fine.  Shut down, back into the hangar.  I was late to fly over the Sierra to meet a guy looking at a Phoenix.  For once, common sense overruled my impulsive nature and decided crossing the Sierra twice with an unknown electrical problem might not be the best idea.  My wife taught me that.

Pulled the left panel again.  Wiggled more wires.  When I wiggled the wire coming from the charge fail light one wire came off the light.  It was loose against the light making an intermittent contact.  Two things broken at the same time just to add to my confusion.  Inanimate objects versus the human race.  Did some internet research.  Rotax says that it is supposed to be a 3 watt incandescent bulb.  Back to Ace.  They had one.  Wired it in, good to go.

I don't know why Phoenix Air uses an led light that they then have to add a resistor to in order to make the charging system work properly.  But definitely the light is an integral part of the charging system.  Bypassing the light didn't work.  The correct light has to be there.

Why did the switch fail?  Kathy said I did something wrong on my last flight.  Aviation rule number one, establish blame.  Well, on the last flight, everything was fine.  I think that the switch just failed because that is what things do.  Then the light said, "lets really screw with his mind".

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Eric Greenwell

I'm surprised a panel light (the 3W lamp) is part of the charging circuit, and not just an indicator. Perhaps the 3W incandescent lamp fails often, and that's the reason for using an LED and a resistor, as the resistor (the part the charging system needs to function) should be more reliable.

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