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Thread: Weird electrical anomaly

  1. #1
    Senior Member c130jake's Avatar
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    Default Weird electrical anomaly

    I finishing my break in 10 hours and first oil change, I flew 3 hours visiting a few local fields and survived my first pavement landings this morning. Hooray!

    After lunch, I went to start up and got no response from the starter and smoke came out the forward throttle slot in the sidewall.

    I checked the key switch, took off the belly panel and looked for signs of melting or burned wires. Everything looked good. Pryed off the left side wall and looked at the wires with a flashlight and mirror. Everything appeared normal.

    Called Mitch. Helped me trouble shoot. Concluded it was after the start solenoid. (Starter cable some where must be shorting) with the help of my Dad and a hangar neighbor, we saw this when the key was turned to start.


    The smoke and smell is coming from where the rear seat post touches the carbon side panel. I forgot carbon fiber is a conductor. It must be traveling to ground where the seat bar touches the fuselage. I will try to post a video. I assume there is a short touching the floor or side panel.



    The picture is looking down from between the fabric and carbon side panel.

    Jake

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    Jake
    Finished CCEX N96FV!

  2. #2
    Senior Member ceslaw's Avatar
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    Default Re: Weird electrical anomaly

    Which wire caused the problem?

    The wire is presumably insulated, so how did it short?

    guessing the wire was not in a fused / breaker circuit?

    Hopefully it will be a quick fix

    keep us posted.

    Chuck

  3. #3
    Senior Member ceslaw's Avatar
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    Default Re: Weird electrical anomaly

    Jake:

    Just watched the video, that helped see the issue.

  4. #4
    Senior Member N867SP's Avatar
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    Default Re: Weird electrical anomaly

    I had a similar issue, minus the smoke. Starter solenoid would pull in (audible cluck) nothing from the starter. Happened once and let plane sit for 20 min and it started right up. Didn't happen again for a few months, then left me stranded. Hand propped it twice to get back home. Ordered new solenoid, dissected old one, nothing abnormal in old solenoid. Replaced solenoid, checked all connections and 30hrs or so without incident.

    It will be interesting what you find. I'd check your grounds as well. I was hesitant with grounding thru airframe, too many connections, so I ran dedicated ground from seat base to starter and skipped the ground strap across the engine mount.


    Pete
    CCK-1865-0078
    ✈️N9PW
    Severna Park, MD
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    Pete
    ✈️CCK-1865-0078 N9PW
    Severna Park, MD W18

  5. #5
    Senior Member c130jake's Avatar
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    Default Re: Weird electrical anomaly

    Well kids, the problem is solved after a day of trouble shooting. I just wish Bud, my hangar neighbor, was around yesterday when this all started. It would have turned nine hours of tearing apart my airplane into a five minute job and I could have flown several more hours of my test phase.

    During troubleshooting, we looked for cooked wires and worn insulation ...none, we isolated the starter solenoid....not the problem, cranked the starter directly with jumper cables. (I thought the starter might be shorted). While checking the starter by bypassing the start solenoid, I noticed a spark where the throttle cable mechanism was touching the left rudder cable. WTF!

    Put the volt meter on it and sure enough, 12 volts on the throttle cable when the start switch was activated. This is when Bud shows up. Former F-106 avionics troop. After explaining what we had been up to, he says "got some jumper cables?" He put the black clamp on the engine mount bolt and the other black clamp on an engine cylinder head bolt and says try it now. Starter works and no more juice in the throttle cable.

    He then says 90% of all aircraft electrical problems are bad grounds. He removed, cleaned and reinstalled the braided bonding cable connecting the engine to engine mount..Bud says it has to be shiny. (I didn't clean it well enough when mounting the engine apparently, worked for awhile during Ops checking and the first 13 hours of flight)

    He said with a bad ground, the voltage was looking for ground, the shortest path from the starter became the throttle linkage which was attached to the carbon fiber side wall which was touching the rear seat tube which was touching the fuselage and therefore the ground. The smoke was the jell coat getting hot where the carbon fiber touched the seat tube.

    Lesson learned, all grounds should be shiny metal on metal and using dialectic grease will help prevent oxidation from ruining your ground connection later.

    Jake



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    Jake
    Finished CCEX N96FV!

  6. #6
    Senior Member ceslaw's Avatar
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    Default Re: Weird electrical anomaly

    Amazing story. Thanks for sharing that. Underscores the importance of the ground connection!

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