Where to look for source of temporary electrical system failure?

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pantdino

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My GM LS3 powered Titan T-51 had an emergency onfield landing after all the electrics including ignition to the engine failed.
Immediately after landing the panel was completely dead with the master switches on, but an hour later everything was functioning normally when the master switches were turned back on.

Where should one start looking for the problem?

Thank you,

Jim
 

Daleandee

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My GM LS3 powered Titan T-51 had an emergency onfield landing after all the electrics including ignition to the engine failed.
Immediately after landing the panel was completely dead with the master switches on, but an hour later everything was functioning normally when the master switches were turned back on.

Where should one start looking for the problem?

Thank you,

Jim

[Let me edit this post ...} At this point most of us wouldn't have a clue where to start ... a wiring diagram would help!
 
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Wanttaja

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My guess is a ground, somewhere. Had an intermittent problem with a Chevy, years ago. Finally found it when I wiggled the chassis ground strap and sparks popped. Only reason THAT happened was because the door was open, thus current would flow to something.

My Fly Baby's generator crapped out on me a couple of weeks back. Ran the Zeftronics measurements for checking the generator, and it was out of spec. Pulled the generator out, re-ran the measurements...and it was then in-spec. In my case, the handling to remove the generator probably got the brushes to seat properly.

Similarly to your aircraft: Probably a connection loose, somewhere, and the impact jarred it back into the place.

Ron Wanttaja
 

Dana

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If everything failed, it's either a primary ground or something upstream of where the positive wiring splits, so that should narrow it down a bit. Did you hear if the main contactor clicked when you cycled the master switch?
 

Hot Wings

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Finally found it when I wiggled
That it the first thing I do with an intermittent.
As has been already noted a complete failure narrows things down a lot. Mechanical relays and switches can be a pain to positively eliminate as the problem. Just because you hear a click doesn't mean that the contacts are really doing their job.
Power up the system and do a voltage drop test across the various bits.
 
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blane.c

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Ground and corrosion.

Sometimes wires will appear fine but under the insulation there will be so much corrosion that after warming up they fail.
 

Dan Thomas

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I would start with that master switch. If it's wired as per typical type-certified airplane, the master grounds one side of the master contactor's coil, and the other side is hot. All it would take is a dirty or loose ground connection at that little grounding wire from the master switch. A little resistance can build heat, which builds more resistance, until the contactor's coil voltage falls far enough that it drops out. And I hope it's not wired with the master switching the hot instead of ground, which would require a breaker or fuse in that hot line before the switch. That's one good reason why they're wired as they are in TC'd airplanes.

This sort of failure is why the FAA requires backup power for EI and EFI in TC'd airplanes. And it's why magnetos are still hanging on in most airplanes. Electrical problems represent 90% of engine problems in cars and trucks.
 

TFF

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Master switch to battery and to busses. How many busses does it run and how are the circuits protected? Relays or direct wiring?
 

rdj

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Engine ground strap (both ends). Battery ground (both ends). Master switch (switches?) Battery contactor. Beyond that we'd need to see schematics of the design and some further data.
 

rv7charlie

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[Let me edit this post ...} At this point most of us wouldn't have a clue where to start ... a wiring diagram would help!
What he said.
And whatever is needed to make the motor run should be independent of the rest of the airframe power routing. Nothing more than the battery terminals should be common to both.
 

Hephaestus

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After checking the above.

Have seen some wierd battery failures that came and went with heat/vibration/internal shorts.
 

Daleandee

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After checking the above.

Have seen some wierd battery failures that came and went with heat/vibration/internal shorts.
Some of the newer batteries with internal protection circuitry will shut themselves off. That's why I still use Odyssey ...
 

Dan Thomas

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If a battery failed, the alternator becomes unstable and the electrical system should have been acting up well before it failed altogether. In this case, the lights just went out, indicating a sudden, total shutdown, which implies the master contactor opening for some reason. Bad battery terminal connections or grounds should show up as hard starting, erratic charging rates, flickering lights or whatever.

Without the wiring diagram it's all just guessing, and simply suggesting a bad battery or some other major component makes no sense. "Bad ground" covers a lot of territory, too. Every component in the primary electrical system has ground connections, so there are lots of them. Some will cause erratic performance, and a few will cause total shutdown.
 

pantdino

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I think this is an example of my ignorance of how aircraft are wired. There was a problem with the right main gear not locking down. Our current hypothesis is that the hydraulic pump therefore stayed on, which evenually overheated the main switch / breaker and cut all power. So toggling off and on wouldn't work until the switch had cooled down, which it did after sitting on the ground for a while.

Per rv7charlie's comment above, this is obviously a bad situation and I'm thinking we will have to rewire the power to the fuel pumps, ECU, and injectors/ignition so they are on their own breaker switch. Does that sound right?

Thank you,
Jim
 

Hot Wings

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Our current hypothesis is << >>
Not good enough. You need to KNOW what caused the problem - then fix it.

You are on the right track by isolating critical systems, but they still need a back up so that they can fail - gracefully. A mechanical switch that fails due to overheat needs to be replaced. A breaker that won't reset until cool after the load has been removed is also suspect.
 
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