Finn Lassen wrote:

Jim Sower wrote:

Finn Lassen wrote:

If one or all of the main rectifier diodes in the alternator shorts out, you will have an alternating current (voltage) feeding the battery and other loads. I sure hope that the "overvoltage" detector will recognize this and kill the voltage to the field winding or disconnect the wire from the B+ terminal.   I'm not sure that ANY OV protection devices will detect failed diodes.  Which one have I missed?

None that I know of :(  Which brings to ... ?

I suspect that the regulators in our alternators are very reliable, providing they are adequately cooled. That would be one advantage for having a external regulator: it can be mounted in a cooler location. On the other hand, I don't know how reliable those "cheap" ford regulators are... Looking at the automotive industry in general, I'm confident that they design their regulators to perform adequately inside the alternator. 

Within certain specified temp limits. Do we know those? I think Tracy mentioned that electronics expected life goes down exponentially with temp increases over 120F... How many of us are systematically exposing our alternators to prolonged idle, AC on, 100F day, NO air moving in the engine compartment?  I'd guess alternators think our environment is like springtime in the Rockies.

I think the importance of this subject is directly related to the $ amount of avionics you have in your plane.  I'm beginning to think it is directly related to the amount of Idle time we have and our inclination to mind-f*** a problem that doesn't seem to exist.
Well, due to the fact that we fly "electric" planes, safety is a factor too. You'll want to be able to diconnect a failing alternator and continue flying on the battery. Time for me to modify my electrical system...  Mine already does that, all by itself, before I even know it's failed ... Jim S

Finn