Electrical problem in flight

Yesterday, I was flying home in my RV-8 at about 6500 feet on a nice, clear day (hazy and hot but otherwise nice). I noticed a burning smell (like melting plastic) but not even a hint of smoke. I throttled back and decended which seemed to improve things (though it was never particularly bad). I then noticed that my alternator discharge light was on steady. I elected to land. I had no issues landing and my radio, GPS, lights and flaps all seemed to work fine.

Now my airplane is sitting a hundred miles from home. I plan to drive back up tonight to take the cowling off and begin troubleshooting the problem. A friend suggested that alternator diodes can smell when they go bad and to check there first. Any other thoughts on what to check first? Any troubleshooting steps or other guidance would be very much appreciated.

Regards,

Bruce

Can't think of any advice other than checking all the wires and fuses/circuit breakers. And check the tension on the alt belt. You might want to take along a battery charger so you can top off the battery.

I found the problem

The alternator's forward bearing was completely destroyed. It didn't do any damage to the drive belt, so the engine was still turning the drive pully, but the alternator was mostly just generating heat rather than electricity. The burning smell was caused by the small plastic electrical connector on the F/E/N terminal melting.

bruce

Thanks for the follow up. Kudos to you for simply putting it on the ground. I'm glad it was such an obvious failure. What kind of alternator?

Electrical Problem in Flight

It is the Van's stock 35amp alternator with the boss mount for the Lyc.

I am planning to buy a new alternator in the next couple days, but have not decided between the Van's "better" alternator and the B&C Specialty L-40 (which is about 2x times the Van's price).

BTW, I would recommend taking a very, very careful look at the alternator during the annual inspection. This plane was annualed two weeks ago and we did not see this problem (though I suspect it had been going bad for some time). My A&I is an exceptionally thorough guy who finds EVERYTHING, but this was a very subtle failure.

bruce

You probably know this, but it's worth mentioning that nothing toasts those bearings faster than having the drive belt too tight.