Alternator/Regulator/Wiring Adventure - Problem Solved

[Davidv]

My alternator and wiring issue was finally solved and I thought detail what happened here so others may avoid the same issue in the future.  The series of events is somewhat lengthy so feel free to skip to the bottom unless you're having a rainy day like we are in Florida.

In Mid-June, I was flying from FXE to BED at FL230 when my LEFT ALT FIELD annunciation went solid red and the LEFT ALT FIELD breaker popped.  As many of you know, the Bravo has dual 70 amp alternators as well as dual batteries.  My JPI was showing 28.8v.  I elected to continue the flight based on the redundancy and VFR conditions.  The solid red is an indication of over voltage.  When I arrived back in Florida I took the plane to my mechanic who did some tests with a volt meter and determined that the issue was with the alternator.  I ordered a overhauled replacement from Falcon Aero through Aircraft Spruce.  On a side note, Bill from Falcon Aero (I believe the owner), was great to deal with and I'd highly recommend them for your future alternator needs.

I received the alternator in Mid July and wanted to get it installed by my mechanic prior to a long trip.  However, my mechanic was tied up so I elected to go to a well known and respected Mooney service center (not in FL).  They removed my old alternator and noticed some burning residue around the alternator and field wire.  As part of the the installation process they also removed the diode at the end of the field wire for cleaning and examination.  The diode was reinstalled along with the alternator.  I started the engine, brought the RPMs up and one again the LEFT ALT FIELD breaker popped as well as a flashing red indication on the annunciator panel indicating no charge.  They pulled the plane back in the hangar and began to troubleshoot.  As part of the troubleshooting they pulled my voltage regulator down from swapped the plugs to the left side of the alternator was going to the right alternator and vice versa.  This resulted in 24V at the end of the field on the left and nothing on the right.  It seemed that my regulator was the problem.  They offered to order me a new one for $2200.  Prior to pulling the trigger, @kortopates recommended I get it repaired at Consolidated Air Supply.  They made the repair a few days later for about $500.  I plugged it back in the plane and sure enough, the same breaker popped.  I sent it back to them to confirm that the regulator was still working properly and they confirmed that it was.

At that point, I was starting to get in that depressed state where you feel like this problem will never be solved without tearing apart half the plane.  I had another mechanic come to my hangar and troubleshoot without success.  Furthermore, after their troubleshooting, I started the engine and now my regulator wasn't working at all (voltage would blow past 30v as I increased RPM).  I didn't want to do any damage so we shut down the engine, swapped the regulator plugs (left side regulator to right alternator) and now it was working correctly but holding at 29.2 which isn't ideal.  

I decided I was done wasting time and money so I flew the plane from FXE to Don Maxwell at GGG since I had faith that Don, Paul, and his team could figure this out.  It only took them a few hours to figure out that the diode at the end of the field wire was installed backwards and was in fact sending electricity in the wrong direction.  At the same time, I had my old alternator bench checked just to confirm that it was in fact the initial cause of my issues.  The alternator was apparently toast with brushes nowhere to be found.  The regulator was being damaged due to the reverse installation of the diode. 

Essentially, the new alternator that I received was in perfect working condition and my issue would have been solved months ago if the diode had not been reversed.  Don replaced the diode with a new one ($0.23), repaired my regulator which had been shorted out again, and now everything works perfectly.  I'm telling this story just to help those in the future and not speak badly about the shop that did the work.  I'm still in discussions with them after the thousands I've spent on this but I have no interest in talking about them here because these mistakes can happen.  It's unfortunate (and sometimes can be very costly), 

[carusoam]

David,

That is a great pirep!
 

Thanks for sharing all the details.

It is incredibly easy to to install a diode backwards... about 50/50 if not knowing every detail required to do it correctly...
 

Usually, the diode is smoked by the time you have the chance to work on it for long...
 

PP thoughts only, smoked a diode out of my tractor tug, once....  Battery had it’s poles reversed compared to standard...  It gave quite a smoke show...  Amazingly the 0.0025 amu part handles so much power, when wired correctly... 

Best regards,

-a-

[kortopates]

David, As Anthony said, great PIREP and thanks for sharing. And you are first class gentlemen!

One question, how long what the diode installed in reverse? And I assume it was reversed with the installation of the new alternator? Bummer to read about that but so glad you are behind that now.

Are you still at 29.2 Volts? That is pretty high.

 

[Davidv]

Thanks Paul, it was installed the wrong way when the new alternator was put in, so about 2 months until it was fixed.  I flew with the left alt field switch off (and obviously the breaker was out).  I'm now at 28.7 volts after Don's team made the repair and so far everything working well!

[Davidv]

Just to close the loop on this, the shop that made the mistake on the diode just sent me a check for all of their original work to install the alternator and troubleshoot the issue.  Even though I spent a lot more, I thought that was very fair of them.  There are a lot of shops/mechanics who would try to play the blame game and this wasn't one of them.

[carusoam]

Great follow-up David!

 

That just reminded me of something....

Diodes are labeled on their exterior to indicate which way the electrons flow.... And don’t flow.

https://learn.sparkfun.com/tutorials/polarity/diode-and-led-polarity

Best regards,

-a-

[Davidv]

2 hours ago, carusoam said:

Great follow-up David!

 

That just reminded me of something....

Diodes are labeled on their exterior to indicate which way the electrons flow.... And don’t flow.

https://learn.sparkfun.com/tutorials/polarity/diode-and-led-polarity

Best regards,

-a-

Thanks, yes I think the root of the issue was when they pulled off the diode to clean the outside.  My alternator had a good deal of something that looked like carbon on it as well as the diode.  They removed the diode to  "clean it up" and possibly removed the labeling in the process.

[thinwing]

interesting....what you are describing is the "antifeedback"diode on the field circuit.The other diodes ,6 in this case ,are internal in the alternator and form the rectifier circuit converting ac to dc.Installing the field circuit backwards (no forward field current from theregulator)would have the same effect as a broken field wire connection,or at least until diode blew either shorting out open or closed.Im assuming diode went closed with regulator trying to dump more and more current thru it till regulator failed.Since most inline diodes are marked with a silver band indicating polarity ,maybe the first shop used a solvent that removed the marking.When 1 or more diodes start to fail in the rectifier circuit,alternator output starts to decrease.....thats the situation I had with the left alternator becoming lazy at idle power.Thanks for report and solution