Did I hurt my alternator?

I had to jump start my plane (using the Piper External Power port) (yes, I
stupidly ran down the juice when I thought a gas smell was coming from a
flooded engine when it wasn't). I turned on just the battery half of the
master while I did it, and the plane started ok.

There was an annoying whine in the intercomm, and it took me a good amount
of time (15-20 minutes flight time) to realize that the alternator guage
was pegged, and cycling the alterator half of the master switch off and on
again got the alterator guage down from being pegged, and got rid of the
whine. I suspect that I misread the sign language from the guy who was
helping with the jump start, and I turned on the alterator before he
unplugged the external power.

Does this damage the alternator in any way?

--
Paul Tomblin http://xcski.com/blogs/pt/
Endless Loop: n., see Loop, Endless.
Loop, Endless: n., see Endless Loop.
-- Random Shack Data Processing Dictionary

"Paul Tomblin" wrote in message
...
[...]
I suspect that I misread the sign language from the guy who was
helping with the jump start, and I turned on the alterator before he
unplugged the external power.

Does this damage the alternator in any way?

I have jump-started countless automobiles without ever disconnecting the
alternator from the battery, never with any damage to the alternator. I
don't know the specifics for the Piper external power connector, but I
suspect it's wired directly to the battery. If that's the case, I don't see
how external power could damage the alternator any more than the battery
itself could.

I don't know why your alternator was being regulated at maximum output (or
something that sounds exactly like that), but from your description it
sounds like it was a transient condition. Perhaps related to having turned
the alternator on before the external power was disconnected, perhaps only
related to the dead battery, or perhaps related to something else (I'd put
my money on the dead battery).

Did the alternator work fine for the rest of the flight? Have you had a
chance to talk to your mechanic yet? If everything's okay now, seems
unlikely that it suffered any damage.

Pete

On Sat, 23 Oct 2004 05:02:19 +0000 (UTC),
(Paul Tomblin) wrote:

I had to jump start my plane (using the Piper External Power port) (yes, I
stupidly ran down the juice when I thought a gas smell was coming from a
flooded engine when it wasn't). I turned on just the battery half of the
master while I did it, and the plane started ok.

There was an annoying whine in the intercomm, and it took me a good amount
of time (15-20 minutes flight time) to realize that the alternator guage
was pegged, and cycling the alterator half of the master switch off and on
again got the alterator guage down from being pegged, and got rid of the
whine. I suspect that I misread the sign language from the guy who was
helping with the jump start, and I turned on the alterator before he
unplugged the external power.

Does this damage the alternator in any way?

Alternators are flakey, they like to blow diodes for what seems like
inconsequential reasons. However, in this case, I suspect the
alternator has not failed. The alternator was probably pegged because
the battery needed a charge. I have jumped my Cherokee 1 time, and
was surprised at how long the ammeter stayed pegged afterwards.

When the master switch is on (so the master solenoid is engaged), it
is a direct connect between the output of the alternator and the
battery. When connected by a low resistance path - a lot of current
can flow between an alternator at 14V and a battery at 8 or 9 volts..
I = V/R, and in this case the R is small, so the I can be large.

All the same, I would put the battery on a charger before flying
again, monitor the ammeter current on your ground ops/runup, and make
sure that the next flight or two are VFR ones.

One last question - does your Piper have a Voltmeter? As long as the
bus is reading close to 14V, the electrical system is probably ok.

-Nathan

I'd be suspicious of the regulator. Somehow it is probably hard over
causing the alternator to go to full output. It isn't the fault of
the alternator that it is hardover. If anything I'd guess the
alternator is OK.

Jump starting is sometimes a complicated art. Yeah, the plug thing
will get things rotating, but a couple of times on Cessnas I've found
that afterwards the alterator wouldn't turn on. The schematics showed
a lot of isolations between the two systems - just why I don't know.

Read your flight manual carefully and study any schematics that might
be applicable.

You may not have damaged your alternator but you may have damaged the
battery. Applying a large current flow to the battery produces
cavitation of the oxide on the plates and will make the paste come off
and settle into the bottom of the cells.
Keep an eye on your battery. It may not hold a charge as well now
over time.

In my 182 if you jump start the plane using the special plug in the side
of the plane the master switch and everything after it are taken out of
the loop. It is as if you already turned the master on. You can see
the charge the alternator is putting out on the gauge. After
disconnecting the cable you can turn the master switch on. If you
turned the master on while still hooked up it wouldn't do anything. I
have a single master. If I had a split master I would still turn them
both on when starting the plane. This is a common topic on the cessna
pilots assoc forums. There is no good reason to start the plane with
the alternator off.

Nathan Young wrote:
On Sat, 23 Oct 2004 05:02:19 +0000 (UTC),
(Paul Tomblin) wrote:


I had to jump start my plane (using the Piper External Power port) (yes, I
stupidly ran down the juice when I thought a gas smell was coming from a
flooded engine when it wasn't). I turned on just the battery half of the
master while I did it, and the plane started ok.

There was an annoying whine in the intercomm, and it took me a good amount
of time (15-20 minutes flight time) to realize that the alternator guage
was pegged, and cycling the alterator half of the master switch off and on
again got the alterator guage down from being pegged, and got rid of the
whine. I suspect that I misread the sign language from the guy who was
helping with the jump start, and I turned on the alterator before he
unplugged the external power.

Does this damage the alternator in any way?