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Burned output lug on alternator


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Interested in your thoughts on what’s going on with my alternator. I recently replaced my aging alternator with an overhauled unit, this is the InterAv. I also put in a new Plane Power voltage regulator. 

I got 3 hours on the plane this weekend. The volts held up between 13.9-14.3. It was fluctuating more than I’d like but not significantly more than in the past. The load meter, however, was showing pretty substantial variations in amps, to the tune of jumping from 10 to 30 with no change in load. On two occasions the volts went to battery voltage and amps to 0 for less than a minute, then came back. Last, there was a notable intermittent whine in the comms that was not there before. I don’t think it was a diode, though, as it didn’t vary with RPM and was intermittent (and this is a newly overhauled alternator).

With the symptoms above I decided to pull the cowling and discovered the melted output lug in the pic below (I believe that’s what it is). This lug had no connections to it.

The A&P I’m working with believes it’s a faulty alternator that is not grounding properly. I double checked the grounding wire and it looked secure, so could it be something internal to the alternator causing this? 

Anyone else see something like this before and have other ideas?

The shop that sold me the alternator has agreed to take it back and repair it. My concern is whether it’s something other than the alternator itself causing this. I don’t want to unnecessarily fry another alternator if its not a fault of the alternator.

 

9B66046F-8E0F-46F8-BC04-871D3315F8EA.thumb.jpeg.a5d817688687a6684cc3333561e17f25.jpeg

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That is your AUX terminal. Was anything connected to it? The AUX terminal is a separate set of + diodes that is used for either regulator voltage sense or for the idiot light or both.

It looks like the insulator failed and shorted the terminal. Most likely a pure alternator failure. You should get a warrantee replacement. 

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I had a similar problem once, minus the fried terminal. Fluctuations in output can be caused by poor power connection, defective master switch or cb. Need to measure the power loss at each junction, with master and field switched on, engine off, if more than .1 volts loss, that may be a problem, alternator would be switching on and off resulting in your output fluctuations. May be corroded terminal or old, half broken wire in these old birds, vibrating on and off when engine is running.

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11 hours ago, RLCarter said:

a bad connection will cause resistance to go up, resistance is heat, was the terminal loose when you took it apart?

The whole red plate was loose, but i think it was because that nut was basically gone. The other terminals over the plate were all tight. 

10 hours ago, N201MKTurbo said:

That is your AUX terminal. Was anything connected to it? The AUX terminal is a separate set of + diodes that is used for either regulator voltage sense or for the idiot light or both.

It looks like the insulator failed and shorted the terminal. Most likely a pure alternator failure. You should get a warrantee replacement. 

No, nothing connected to it. Only connection was to the terminal below the burned terminal. The shop that sold me the alternator agreed to take it back and repair at no cost, but obviously annoying to have to incur more labor for a faulty alternator. 

9 hours ago, Smiles201 said:

I had a similar problem once, minus the fried terminal. Fluctuations in output can be caused by poor power connection, defective master switch or cb. Need to measure the power loss at each junction, with master and field switched on, engine off, if more than .1 volts loss, that may be a problem, alternator would be switching on and off resulting in your output fluctuations. May be corroded terminal or old, half broken wire in these old birds, vibrating on and off when engine is running.

Will for sure be checking this as well. If it means anything, it seemed like the amps were more stable at a low power setting on the ground with a light load. 

8 hours ago, Freemasm said:

Going by memory here but I think some of the older Prestolite based units have an AC terminal about where (I think) your picture is indicating.  If anything is connected there you're shorting straight to ground and would cause some of the issues you're shown/described. Yes, it's a long shot based on the mounting bracket shown.  Can you tell us what nomenclature is stamped next to the lug?

Here is a picture i found of identical alternator with an arrow to the lug that burned. There is a connection at the lug directly below, but there wasn't anything connected to the burned lug. image.thumb.jpeg.08164fc6dc255117d88746796e08e721.jpeg

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I think Rich nailed it too, but...

Lets look really close where something shorted against something else....

We have two alternator covers pictured...

The black one, almost nicely labeled....

The red one, indicating where the shorting occurred over a period of time....

Did the arc occur to the red piece? What allowed the arcing to the red piece? (If I am Seeing that correctly)

Being only a PP, I am not familiar with what goes where with the arrows not really pointing directly at the lugs...

I would be concerned about hooking up a new alternator and having it ground out the same way...

It seems as if some piece of connecting hardware may be too large and is touching where it shouldn’t in flight?

Sorry if I opened more questions, than answers...

Best regards,

-a-

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The Interav parts list shows a fiber insulating washer held in place with a star washer and nut.  Same as the output lug.  Obviously the washer was missing an the plate and lug tried to weld themselves together.  No wonder the amps were fluctuating.

I got the Interav Install guide, also the troubleshooting and repair manual.  About 40 pages.

Edited by David Lloyd
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