Dropped my wife and 3 of her friends off 45 minutes from our place to spend the night at a spa. On descent on my return to home base my right alternator light flickered a few times, the left alternator amps started fluctuating and the autopilot disconnected. The right ALT light never illuminated again but the amp meter showed zero amps. I couldn’t get it to reset. I was VMC so no big deal.

I just replaced this alternator 5 hours ago so I thought what the heck? It’s new.



Guessing that was an impressive arc going on in there for a few seconds. The stud-end inside the alternator failed. Infant mortality. Poor quality control at Hartzell strikes again. I’m guessing the warranty doesn’t cover labor. Grateful there wasn’t a source of fuel near the arcing alternator.

The spa trip just cost me some more AMUs!

Kirk

I had a very similar failure where the nut did get tightened correctly and it cut the stud in half...

Found it before full failure stud was cut 7/8 through and alternator was intermittent.

Thanks for sharing. I recently had one installed. I think I'll be giving it a good look on pre-flights for a while.

Have your mechanic complete FAA form Malfunction and Defect report documenting the failure. This gets the early failure into the FAA tracking system and enough similar failures warrants FAA investigation.

Where are they built? Ford used to build some amazing alternators for Piper years ago. They were built Ford Tough! A TriPacer that I flew had one that lasted for over 40 years!

Really hard to tell from the posted picture, but if the stud remnant in the alternator case is not loose, I'd say this was an installation failure, not an alternator failure.

Also if the stud is not loose and there is arc evidence in the perimeter of the hole in the cable end lug, I'd again lean toward installation error not alternator fault.

IE the cable was not tightend correctly, or over tightened and stripped the nut or stud.

Here’s a better pic. Mechanic said it was definitely an internal issue. (Not the same mechanic or shop that installed it). We’ll see what Hartzell says when they see it.

Kirk

Looks like an internal assembly error to me. You'd have to really wrench on the top nut to break that stud and even then it would be more likely to fracture on the outside.

Is the wire lug still tightly attached to the remaining portion of the stud (under the boot)?

Hi Lance - Yes, still attached.

Then unless the stud was fractured by over torquing the outer nut (which I think is unlikely) the alternator came to you with a problem waiting to happen. From what I saw in your pictures I'd guess that the internal connection to that stud was loose enough to generate a small resistance. With resistance in the alternator output, the VR would just crank up the field current until that peaked or the alternator was putting out enough extra voltage to bring the bus up to the setpoint. 40A through a 1Ω resistance dissipates 1600 W, definitely enough to fry the stud. That would also mean the alternator was actually putting out an extra 40V but given enough RPM they will easily do that as long as the diodes survive.

If the lug is still attached then my previous speculation is 100% wrong.
I had a similar failure where the lug was loose and cut through 7/8 of the stud.
It could have easily looked like yours if it was flow a bit longer.

Don't feel bad Kirk, those AMUs were going to be spent either way. Just be glad it didn't happen on a passenger leg.