Alternator goes out... ... and then comes back

I believe that somehow you tripped the over voltage relay.
That whams the alternator off line positively
until something is cycled. Even a momentary over voltage
will do it.

So the symptom then is as you had, there is no "load."

The "something" that is cycled will either be the alternator
switch or master switch. Check you POH. On older 14v planes,
it's often the master switch that must be cycled.

The overvoltage protection is there to keep the alternator
from ripping the **** out of everything if there is a failure
in the regulator or wiring that would command full output
from the alternator. Generally, they are set around 16v.

The most common reason for ov tripping is water in the battery
too low. Since you charge like a bandit, I think that's not
your problem.

When it was at full scale, you could have momentarily throttled
back to reduce rpm... I'd have expected the load to drop a bit. A
low battery could peg it out for awhile as the other poster pointed
out.

Bill Hale BPPP instructor A&P