High Voltage

(Dan Thomas) wrote

(Jim Rosinski) wrote
Today while descending from a leaf-watching flight at 13K down to 5K,
the "high voltage" indicator flickered for about a minute and then
went out. It has never done that before. I forgot that a useful
procedure is to cycle the alternator half of the master switch so I
cannot report a result of having done that. Throughout, alternator
readings were fine, and battery water levels checked fine after the
flight. A brand new voltage regulator was installed 3 years ago.

Thanks in advance for any advice on what might be wrong, or
appropriate further courses of action (obviously talking to my
mechanic is high on the list). The airplane is a 1972 Skyhawk. BTW,
googling for "high voltage" gave some useful results, but inadequate
so I thought posting would be appropriate.

Worn alternator brushes. How many hours on the alternator? How many
with lots of load, such as night flying?

Alternator has about 1800 hours and 22 years on it, so your suggestion
sounds reasonable. My hangar neighbor also suggested a loose
alternator belt, which I have yet to check. Both suggestions seem
consistent with the low rpm experienced during a long descent, which
was when I noticed the flickering.

Jim Rosinski

(Jim Rosinski) wrote in message . com...
(Dan Thomas) wrote

(Jim Rosinski) wrote
Today while descending from a leaf-watching flight at 13K down to 5K,
the "high voltage" indicator flickered for about a minute and then
went out. It has never done that before. I forgot that a useful
procedure is to cycle the alternator half of the master switch so I
cannot report a result of having done that. Throughout, alternator
readings were fine, and battery water levels checked fine after the
flight. A brand new voltage regulator was installed 3 years ago.

Thanks in advance for any advice on what might be wrong, or
appropriate further courses of action (obviously talking to my
mechanic is high on the list). The airplane is a 1972 Skyhawk. BTW,
googling for "high voltage" gave some useful results, but inadequate
so I thought posting would be appropriate.

Worn alternator brushes. How many hours on the alternator? How many
with lots of load, such as night flying?

Alternator has about 1800 hours and 22 years on it, so your suggestion
sounds reasonable. My hangar neighbor also suggested a loose
alternator belt, which I have yet to check. Both suggestions seem
consistent with the low rpm experienced during a long descent, which
was when I noticed the flickering.

Jim Rosinski

1800 hours on an alternator that's probably never been opened is
a fairly positive affirmation that the brushes are shot. We check ours
every 500 hours, and find that after two checks (1000 hrs) the brushes
are far enough gone that we won't leave them for another 500.
Better get them changed before one of them comes out of its guide
and the spring chews up the slip rings. Things get more expensive at
that point.

Dan