I have been having an intermittent and slowly worsening problem with high voltage. Over most of the last 30 hrs or so it settled in around 14.6 or 14.7 volts. But on yesterday's flight home from Mammoth I noticed it hovering around 15V and some of my avionics were acting up, so I decided to do a little alternator out experiment.
I turned off the alternator and all unnecessary draw - radio, strobes, Blue Mountain EFIS, electric AI. I kept on the engine instrumentation, transponder, music (a most critical item given the beauty of the sunset), audio panel, rocky mountain microencoder, and trio auto pilot (also allowing me to more fully enjoy the flight). I was showing 8 amps to run the engine bus (coils and injectors).
With my 33 amp hour Panasonic SLA battery I flew for 45 minutes and 200 miles over the Sierras, passing dozens of airports, and into the LA basin before it got dark enough that I decided to turn the lights on. The plan was to turn the alternator back on when the voltage dropped below 11.5 volts but it never dropped below 11.9V. It did charge at a brisk 60amps when I turned the alternator back on so there couldn't have been too much time left. Still, that did quite a bit of confidence building regarding the ability to carry on in the event of an alternator failure.
I also set a personal record for the most beautiful and clear sunset I have seen while flying. I could see San Nicholas Island from over 150 miles away.
Time to install a spare alternator.
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