Originally Posted by Kendel_McCarley
Plane Power has some good troubleshooting flowcharts. It'd be good to work through the appropriate flowchart to verify it's the alternator and not some other component that's causing the charging issue, before throwing money at repairing or replacing it.

https://planepower.aero/aircraft-alternator-support/troubleshooting/

Thanks, I really appreciate that. But it confirmed what I'd concluded -- that if the alternator field terminal has about 12 volts (the troubleshooting guide said that 1 to 1.5 volt drop through the regulator from the supply voltage is ok) and the alternator output (battery) terminal has (the abnormally low) bus voltage, then it should be putting out current to raise the bus and battery voltage. Of course, that's also assuming that the battery and alternator grounds are intact which they are. I'd be really, really happy if the problem was something else, but no matter what else might or might not be going on, the alternator flunks the basic test.

Roy

States where I've landed my 150
[Linked Image from eznec.com]