Alternator Fooled Me

[Steve Ashby]

Jon,
I am really thinking of a butt splice so there would be nothing to vibrate loose. If I ever have to replace the alternator, I would just cut out the splice and use another one, losing less than inch of wire (hence the service loop). Just a thought.

[BillL]

Originally Posted by vlittle

Gold terminals are not the solution. Gold migrates under high current flows, so it usually restricted to non-power applications. As for RTV potting, use 'sensor safe' product, but not generic silicone that uses acetic acid (vinegar smell).

Gold: Yeah, I was not sure about that, I was thinking wear from motion and oxidation. Thanks for the clarification. I am getting a quote and will change to the tin coated terminals.

Potting RTV formulation: Good to point out Vern. I neglected to mention.

Originally Posted by Steve Ashby

Jon,
I am really thinking of a butt splice so there would be nothing to vibrate loose. If I ever have to replace the alternator, I would just cut out the splice and use another one, losing less than inch of wire (hence the service loop). Just a thought.

The PP that I have uses 2.3 mm male spade terminals in the alternator, Steve. Are you talking about eliminating the connector housing and just using the direct to terminal connections? If so then all the wire forces will be transmitted to the spade terminal and it may not be up to it. Best to just just consider potting the connector. I have no facts to say this is a valid fix to eliminate the root cause failure, but it should help.

[DanH]

If I was going to eliminate the plug at the regulator, I'd probably clip a heat sink to each pin in turn and solder a wire, then sleeve it with heat shrink, then pot the entire plug cavity. That would allow relocating a plug or splice someplace with limited vibration.

It appears to be what E-Mag does to the socket and pins on the Ford EDIS coil used on a p-mag.

[JonJay]

Just as another point to consider, if you have a cross over exhaust, that connector is a only a couple inches in front of it on the PP unit. I used a heat shield to help mitigate the heat radiation. Also, I tested the potted regulator with a heat gun to the point of melting the potting. The regulator still functioned fine.

[Lynnv]

Dan, I probably should've posted this a couple of years ago when it happened. I had a similar failure with my Plane Power alternator. Same thing, flying over mountains in Colorado on my way to Gunnison. I was about 100 miles out when I get a "low Volts" indication. I cycled both the alternator switch and the ALT circuit breaker, no change. So I shut everything off, (dual mags), and continued to KGUC. After un-cowling and checking about everything I could think of, i charged the battery and flew home. (No charging on the way home either.)
Back at the hangar, I traced the field wire from the Split switch (Cessna type), to the terminals in the plug on the back of the alternator. "0" volts. I thought I had found the problem. (Switch). When the new switch came, I installed it and it worked. Problem solved?for about 5 minutes of flying. It quit again
Back to the hangar. This time I removed the alternator and sent it to Plane Power to have it checked out.
It came back with a clean bill of health. After installing and starting the engine, it still didn't work.[php]
Previously, I had checked the field (red wire) on the plug, and it had battery voltage. I decided to look again. I must be missing something where the wire enters the back of the plug. Then I found it! Where the red wire enters the back of the plug - a small part of the terminal end was protruding out from the back side. I pulled on the wire, and the terminal connector was broken! That was it!
I called and ordered a new plug, with enough wire on it to go all the way back to the split switch. It now charges normally! Whew!

[Berchmans]

For the last month I have had the same problem only it was intermittent with the alternator coming and going. Saw this post on Friday, tweaked the connector on Saturday and the problem is solved. Thanks, I never did get to the point of pulling the alternator so once more the Van's Air Force did the leg work for me. Now if I could just find someone to polish the plane.

[DanH]

Follow up: Tweaking the connector didn't work long term. Actually, it didn't work very long at all...maybe 10 hours.

Cut the plug off the harness and dissected it. Here's what the connectors look like when out of plastic housing. You're looking at top and bottom:



I un-bent the terminals to spread them open:



When spread open, here's the "spring" which is expected to maintain contact pressure:



The two contact surfaces of the field connection (face of the spring and the underside of the housing), lighted two different ways for contrast. There is no sign of overheating, just what appears to be fretting:





Sense terminal for contrast, which carries a lot less amperage:



Continued.

[DanH]

The plastic plug itself, with its rubber gasket, appears to be firm in the regulator socket...no relative movement, no way for vibration to cause a problem. The issue appears to be that the above female terminals are simply snapped into the plastic plug, without any additional fixation. I think they are fretting and oxidizing the contact surface. I'm also going to look at "pinch" tonight, the degree to which the spring puts pressure on the contact area. I'm suspicious about the relative dimensions; thickness of the regulator pins vs the socket.

Even if the the contacts were not fretting, the wires need additional support in the plug. The white wire below is the warning light terminal; note that it has almost fatigued to total failure:



The surprising thing is how it fatigued with the wires secured as they were. All the terminal wires were zip-tied together about an inch from the back of the plug, then zip-tied to the B-lead a few inches further away, then the whole bundle was shrink-wrapped and held with an Adel clamp at the engine case split line.

The above terminals are now with a buddy at Plane Power, who will take it up with the engineers.

A new replacement plug did not incorporate any fixation, so I've potted it with a solvent based rubber compound.



Anyone believe dielectric grease in the sockets would be a good addition?

[Doug]

Dan,

Dielectric grease is worthwhile especially since there is a risk of moisture with contacts that do not appear to be gold plated. Good idea - in fact I will call into my local auto parts store today to pick up a tube.

[strahler13]

I had a similar problem. Checked, then replaced wires to the alternator. Intermittent problem would not go away. Met Bill from B&C at Oshkosh. He told me to replace the alternator plug. I told him I checked that and the wires were fine. He said REPLACE THE PLUG. He actually gave me a new plug. We replaced the plug and no further problems.