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  #1  
Old 10-16-2019, 10:17 AM
rdrcrmatt rdrcrmatt is offline
 
Join Date: Oct 2014
Location: Milwaukee, WI
Posts: 251
Default Strange combination of issues

Our RV-10 has been working great for 2 years.

The system is EarthX PC680, Recently replaced main contactor (from ACS), Plane power 60a alternator, VP-X Pro, Garmin GTN650, GTR20 Remote Radio, Dual GDU460 (G3X).

The issue was first reported as BOTH COM radios getting X'd out. When I fired the plane up (engine off), COM2 was faulted with a "short circuit" but I reset it and it was fine. I could not replicate any issues. The last person who flew the plane had the radios get X'd out around the time of being handed off to departure.

After starting the plane, everything seemed okay until I tried to taxi. Advancing the throttles causes the amp reading on the VP-X screen to increase dramatically and then it cuts them both out with "short circuit".

Here's a video. https://youtu.be/q11zGFy63vU

One thing I notice right away, is that the system voltage finally gets up to 13.8 only as the engine finally hits over 1700rpm. In the past it would hit 14.1 at nearly idle RPM. NOTE: The data here is at 1 second intervals, before anything has time to go wonky. It's just an example of the lower than previous voltages.



At first this seems like belt slippage, voltage regulator, or alternator failure. But the Coms shorting out has me completely thrown for a loop. Thoughts?
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Last edited by rdrcrmatt : 10-16-2019 at 10:27 AM.
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  #2  
Old 10-16-2019, 11:36 AM
spatsch spatsch is offline
 
Join Date: Nov 2014
Location: Randolph, NJ
Posts: 205
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I had a similar issues with nearly an identical setup Alternator/VP-X/EarthX but with a Dynon rather then Garmin.

In my case the transponder would indicate a short circuit. The fix was to replace the Alternator.

I am still not 100% sure how it hangs together but the theory is that very short alternator spikes caused by a regulator on its way out can cause short current spikes which the VP-X is sensitive enough to trigger a short circuit but not long enough to harm anything else (or trigger a mechanical fuse).
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  #3  
Old 10-16-2019, 12:19 PM
rdrcrmatt rdrcrmatt is offline
 
Join Date: Oct 2014
Location: Milwaukee, WI
Posts: 251
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Quote:
Originally Posted by spatsch View Post
I had a similar issues with nearly an identical setup Alternator/VP-X/EarthX but with a Dynon rather then Garmin.

In my case the transponder would indicate a short circuit. The fix was to replace the Alternator.

I am still not 100% sure how it hangs together but the theory is that very short alternator spikes caused by a regulator on its way out can cause short current spikes which the VP-X is sensitive enough to trigger a short circuit but not long enough to harm anything else (or trigger a mechanical fuse).


Thanks, that's sort of where I'm leaning at this time.

I'm going to go test the plane again. This time try to run the engine up with the alternator off to see if that isolates the problem.
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  #4  
Old 10-16-2019, 12:29 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,111
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Alternator system would be my first check, in depth. Remove and bench test it. Check for AC content (>.03v), ground the F terminal and see if the voltage rises, remove the rear shield, check the brushes, and check output between the three phase leads while operating. They should be equal within .01 volts.

I made a bench in about 20 min with a 2X6 3', couple of 2x4 blocks, and a spare electric motor I use as a buffer. Hook with an amp meter, volt meter to any lead acid battery. Be sure the connections are solid, not clips, and you are in business. It will take maybe an hour. To set up, debug, test and put away.
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RV-7
1st Flight 1-27-18
Phase II 8-3-18
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Instrument Currency 12-17-18
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Last edited by BillL : 10-16-2019 at 12:39 PM.
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  #5  
Old 10-16-2019, 03:24 PM
svyolo svyolo is offline
 
Join Date: Oct 2017
Location: bellingham, wa
Posts: 150
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I have spent enormous amounts of time and money troubleshooting and replacing expensive electrical parts, only to discover, in the end, a dirty or loose ground.

30 years of doing stuff, and it still gets me sometimes.
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  #6  
Old 10-16-2019, 05:46 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
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Quote:
Originally Posted by svyolo View Post
I have spent enormous amounts of time and money troubleshooting and replacing expensive electrical parts, only to discover, in the end, a dirty or loose ground.

30 years of doing stuff, and it still gets me sometimes.
Note in my post I said "good connections"? When testing a PP alternator on my "bench" I was using some alligator clips. It was impossible to get a good, consistent voltage out of the unit and had to make jumpers with proper connectors/crimps and tighten all the fasteners. Then it made the correct voltage. It truly is sensitive to the ground of the alternator back to the battery. In a way, it is a bad design to breakout the field supply with a single wire from the alternator. Just think about all the connections that have to be perfect . . . . .

This alone should not cause trouble with the radio, but add a little strange behavior of that X battery protection system, who knows.
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RV-7
1st Flight 1-27-18
Phase II 8-3-18
Repairman 11-15-18
Instrument Currency 12-17-18
Shrunken Exit = ??
No Photo? => PM me.
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  #7  
Old 10-17-2019, 01:10 PM
rdrcrmatt rdrcrmatt is offline
 
Join Date: Oct 2014
Location: Milwaukee, WI
Posts: 251
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Thanks guys,

I tested again with the alternator field OFF and the problem did not happen again. That, in addition to the lower than normal volutages leads me to think replacing the alternator is in order.
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  #8  
Old 10-17-2019, 02:05 PM
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hgerhardt hgerhardt is offline
 
Join Date: Oct 2006
Location: torrance, ca
Posts: 516
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Probably one of the 8 rectifier diodes in the alternator is bad which: 1) limits output, especially at low RPM, and 2) bleeds AC voltage into the bus which the radios don't like.

If this is the culprit, need to replace the rectifier in the alternator.

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  #9  
Old 10-17-2019, 02:23 PM
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jdeas jdeas is offline
 
Join Date: Mar 2006
Location: SoCal
Posts: 618
Default PP alternator stator windings

There was a problem with some of these units a few years back with vibration breaking the stator lines. When the first one goes you get some weird voltage and noise issues due to loosing a phase. When the second one goes you loose the alternator.


Been there. A visual inspection around the back edges (view through cooling slots) was all I needed to see the broken wire between the coil and the internal regulator. If this is it, another broken line and full failure is not far off.
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Last edited by jdeas : 10-17-2019 at 02:34 PM.
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