Ground getting energized

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startingovercfi
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Ground getting energized

Post by startingovercfi »

We had an unusual problem in our DA40 that none of our mechanics/IAs have seen before.

After engine start smoke started coming from cowling.

The mechanics determined that the ground somehow got energized and heated up the metal fasteners on cowl melting the fiberglass,

They don’t know what to replace or how to troubleshoot,

If we put master on, everything powers up normally.

We did just change out the alternator.

Anyone seen this problem before?
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astaib
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Re: Ground getting energized

Post by astaib »

How is connected the new alternator ?
F1
F2
Ground
Aux
??
Is it a lyco version ?
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Charles K
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Re: Ground getting energized

Post by Charles K »

Did you put in a plane power 150A alternator. That alternator's positive terminal will short out against the air vent metal pipe for the alternator. The plane power alternator does not need that. Another member here tipped us off to that. I let shop know when they put it in and they had that part cut shorter and welded shut (the PP alternator does not need the outside cooling air - it has two built in fans.
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startingovercfi
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Re: Ground getting energized

Post by startingovercfi »

Charles K wrote: Fri Apr 09, 2021 10:26 pm Did you put in a plane power 150A alternator. That alternator's positive terminal will short out against the air vent metal pipe for the alternator. The plane power alternator does not need that. Another member here tipped us off to that. I let shop know when they put it in and they had that part cut shorter and welded shut (the PP alternator does not need the outside cooling air - it has two built in fans.
That is the one we installed. Good lead. I will have them take a look at that. Thanks.
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Steve
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Re: Ground getting energized

Post by Steve »

Wow, that is amazing, but it makes sense. Our composite cowling could act as a resistive load between an inadvertent B+ contact point and ground through one of the Dzus fittings. Unlike a metal cowling it wouldn't cause a dead short.

An important reminder to check clearances when working under the cowl...
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startingovercfi
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Re: Ground getting energized

Post by startingovercfi »

The essential bus breaker was popped. Does that help any? Still troubleshooting :scream:
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