Alternator failure

[PeytonM]

1989 M20J. 3300 TTAF.  I lost my alternator after a 2 hour cross country, thankfully only 10 miles from my destination. Landing was uneventful.  Upon examination, I found a broken connection to terminal F2 on the alternator. Photos below.  440TT since new alternator. Any thoughts on causes or prevention?

 

[N201MKTurbo]

That is the most common cause of alternator failure. Just use good terminals and dress the wires so there isn't a lot of wire dangling off the terminals. if you can tie it to the big wire it will support it so it won't vibrate apart again.

I'd replace the field wires back to the regulator and get rid of all the splices.

Edited November 28, 2017 by N201MKTurbo

[laytonl]

+1. Splices in the field circuit are a problem waiting to happen!  Lee

[jaylw314]

Looks like the connector died from vibration in the wire, it broke right where the wire terminates.  Too bad we can't use the super-fine stranded silicone-insulated wiring that's common in RC heli and drone use.  I'm guessing that stuff would be MUCH more vibration/fatigue/heat resistant than normal stranded wire, and the better flexibility would mean less strain on the connectors as well. 

[Raptor05121]

That looks like your field wire. Sadly, just use a nice connector and be sure not to bend them during installation. Should be a quick 2-min fix.

I see you have the blast tube still on yours. I took mine off.

[aaronk25]

My mechanic checks these at every oil change. Finds them loose about every 150 hours. Prevention = check check and check again!


Sent from my iPhone using Tapatalk Pro

[Jerry 5TJ]

In my E model I used two ring terminals back to back and two field wires in parallel to a point they were well-supported in the wire bundle. 

[cliffy]

If I could be honest with you?

I see lots of things that I don't like in that wire bundle you show. I see 1 splice that looks like it is wrapped with blue painter's tape. I see a splice in the wire that broke that seems to have bare strands exposed outside of the splice insulator. I see splices that don't look like they are crimped properly. Some of the wires look to be old and brittle with surface cracking. I see a rushed and quickie job of trying to tie up the entire bundle with little thought to smooth wire flow and professional appearance. It doesn't look like a real A&P was the last to work on that bundle of wires. 

I am not a fan of crimp splices as they tend to create problems down the line with age. Soldered electrician splices (as shown in 43.13) are my favorite. More work but they don't fail. I once worked on a Twin Comanche that had 5 splices in 1 foot or wire in the wheel well going to the green light switch! 2 of them were loose.

Yes to replacing the ring eye BUT only after eliminating the extra splice close to the final connection and going ahead and cutting all the plastic ties, changing the incorrect connections and rerunning and securing the wiring in a professional manner. 

You will be money ahead and safer in the long run to have it all done correctly now rather than just a quickie ring eye fix.

Nice that it happened near destination. My last one was not that close to home. Had to down load all electrics and save the battery for radio upon landing (Charles Atlas gear and flaps :-) Luckily for me it was a clear and 50 day.

[PeytonM]

Thank you everyone for your honest feedback and great suggestions. Honesty is always the best policy, and the safest one, too. 

[nels]

I'm not an aircraft mechanic but what I see is the terminal eyelet broke not the wire. The eyelet it made of copper with a lead coating. Copper fatigue cracks and breaks from vibration quickly. The threaded post isticks out too far from the top of the nut not allowing the silicone rubber shield/ vibration dampener to fully engage around the nut which would have stopped the vibration and hence stopped the failure. What I think is missing is another nut. The wire should be between the two nuts. The additional nut would essentially shorten the threaded exposed stud and would allow the dust silicone cover to engage securely on the top nut which would stop the vibration. Pretty picky I know, but I think I'm right.

[PeytonM]

Wow. That’s pretty interesting, and it makes sense. I wonder if others have their alternator connections set up that way. 

[Jim F]

PaytonM

looks like you are missing the cooling air SCAT hose. It connects to that 90 degree 1inch tube on the back of the Altenator and to the engine baffel tube.  The fan on the front throws air out when spinning and you want cool air in the back. 

Jim

[jetdriven]

M20J is not supposed to have  a cooling fan nor a cooling hose. The air from the front of the alternator is higher pressure air. It forces itself through the alternator. 

[jetdriven]

On 11/27/2017 at 8:28 PM, N201MKTurbo said:

That is the most common cause of alternator failure. Just use good terminals and dress the wires so there isn't a lot of wire dangling off the terminals. if you can tie it to the big wire it will support it so it won't vibrate apart again.

I'd replace the field wires back to the regulator and get rid of all the splices.

Adel clamp the field wire to the alternator case right before it goes onto the alternator terminal and it won’t break again. Lycoming field wires last 300 hours before they break at the terminal beucause they’re not supported and the wire strands fatigue. 

Edited November 29, 2017 by jetdriven

[Jim F]

Jet driven,

thanks for get correction

jim

[Yetti]

Think of the engine as one moving part and the airframe as another.  Wires should be routed as close to center of that movement as possible.  The landing light wire can break terminals.  Eliminate wire movement at all possible points. Fix the rats nest.

Edited November 29, 2017 by Yetti