Alternator Noise

I know that this is another frequent topic, but I'm hoping that someone
can help narrow this down for me.

I have a rebuilt Chrysler alternator (from Electrosystems) on my
Cherokee that was installed about 400 hours ago. However, I am
experiencing alternator whine that varies with engine speed, but which
disappears completely when I turn off the alternator side of the master
switch. In addition, increasing electrical load seems to make it worse.
I have replaced the filter capacitor on the alternator output with a new
one (15uF) and it doesn't seem to have made much of a difference (the
filter is grounded to the alternator).

My mechanic took a look at the alternator at the last annual inspection
and thought that the cooling fins were backwards (auto style, not
aviation style). Not sure if that's normal for the Cherokees or not,
but I can't believe that Electrosystems would do it wrong.

How long should I expect this alternator to last? Does this sound like
a rectifier problem that would warrant replacement of the alternator
after just 400 hours? Could it be a regulator problem? Any suggestions?



Thanks,
JKG

On Sun, 05 Dec 2004 22:42:57 -0500, Jonathan Goodish
wrote:

My mechanic took a look at the alternator at the last annual inspection
and thought that the cooling fins were backwards (auto style, not
aviation style). Not sure if that's normal for the Cherokees or not,
but I can't believe that Electrosystems would do it wrong.
I also have a Cherokee with a Chrysler alternator. They should be
"aircraft type" as your mechanic puts it. If they are installed
wrong, you will not get good cooling and could have burned something
out prematurely.


How long should I expect this alternator to last? Does this sound like
a rectifier problem that would warrant replacement of the alternator
after just 400 hours? Could it be a regulator problem? Any suggestions?
Alternators life depends on many things, but if your re-build was done
right it should last more than 400 hours. If the fins aren't pushing
air the right way it could warrant another re-build. From just what
you've described, it does not sound like a regulator to me, but I'm no
expert, just someone who got a re-build a couple months ago because of
a whine, and variable voltage output.

If you have a descent rectifier repair shop (alternators, generators,
starters, etc.) in your area, take the alternator to them and have
them bench test it. In about 10 minutes they can tell you anything
and everything that is wrong with it.

HTH and Good luck.
z

Find or purchase a clamp on amp meter that will read both AC and DC
amps. Turn on enough loads so that the alternator is generating at
least 50% of it's rated load. Measure the DC amps and the AC amps of
the alternator output. The AC current should not exceed 15% of the DC
amps. If it exceeds 15% then you have a bad diode or stator winding.
In many cases you can not get 50% of rated output if you have a bad
diode.
John




On Sun, 05 Dec 2004 22:42:57 -0500, Jonathan Goodish
wrote:

I know that this is another frequent topic, but I'm hoping that someone
can help narrow this down for me.

I have a rebuilt Chrysler alternator (from Electrosystems) on my
Cherokee that was installed about 400 hours ago. However, I am
experiencing alternator whine that varies with engine speed, but which
disappears completely when I turn off the alternator side of the master
switch. In addition, increasing electrical load seems to make it worse.
I have replaced the filter capacitor on the alternator output with a new
one (15uF) and it doesn't seem to have made much of a difference (the
filter is grounded to the alternator).

My mechanic took a look at the alternator at the last annual inspection
and thought that the cooling fins were backwards (auto style, not
aviation style). Not sure if that's normal for the Cherokees or not,
but I can't believe that Electrosystems would do it wrong.

How long should I expect this alternator to last? Does this sound like
a rectifier problem that would warrant replacement of the alternator
after just 400 hours? Could it be a regulator problem? Any suggestions?



Thanks,
JKG

Jonathan Goodish writes:

I know that this is another frequent topic, but I'm hoping that someone
can help narrow this down for me.

I have a rebuilt Chrysler alternator (from Electrosystems) on my
Cherokee that was installed about 400 hours ago. However, I am
experiencing alternator whine that varies with engine speed, but which
disappears completely when I turn off the alternator side of the master
switch. In addition, increasing electrical load seems to make it worse.

You could have lost a diode. There are 6 main diodes, usually molded
into a unit.

If you have a friend with a portable oscilloscope, it's an easy test:
load the alternator and look at the waveform. You'll see the chunk
missing as compared to http://www.medar.com/images/3phase5.gif

Or pull the alternator [disconnect the battery ground FIRST, please..]
and take it to an alternator shop. [NOT a chain auto parts store
who has an alleged tester.] They should be able to spin-test it.
AFAIK, having a test done by a non-FAA-anointed shop would be legal.
(Having them fix it, of course will get you sent to Gitmo..)

http://www.windstuffnow.com/main/3_phase_basics.htm

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

On Mon, 6 Dec 2004 06:15:07 +0000 (UTC), David Lesher
wrote:

Or pull the alternator [disconnect the battery ground FIRST, please..]


Why is this important? What will happen if you don't disconnect the
ground first?

Also thanks for the link on understanding the alternator!

z

Well lets say you are a hot shot mechanic and disconnect the hot side
of the battery first with your handy dandy metallic wrench. Some
sweet young thing walks by and distracts you for an instant and the
wrench handle contacts the battery box or some other part of the
airframe. There will be a big flash as a couple of thousand amps
flows in the wrench handle. A hole will appear in the aluminum
airframe or battery box where the wrench contacted it . This is bad
but what happens next is worse. The flash is next to a battery vent
cap and the O2 and H2 gas inside the battery ignite and blow the top
off of the battery spraying battery acid in your eyes and all over
the airplane.
Need I say more?
John

On Mon, 06 Dec 2004 16:48:03 GMT, zatatime wrote:

On Mon, 6 Dec 2004 06:15:07 +0000 (UTC), David Lesher
wrote:

Or pull the alternator [disconnect the battery ground FIRST, please..]


Why is this important? What will happen if you don't disconnect the
ground first?

Also thanks for the link on understanding the alternator!

z

All of which is much less likely if you've disconnected the ground first.
That way, you'll have to hit both battery terminals simultaneously to
experience John's scenario.

Jon

"John_F" wrote in message
...
Well lets say you are a hot shot mechanic and disconnect the hot side
of the battery first with your handy dandy metallic wrench. Some
sweet young thing walks by and distracts you for an instant and the
wrench handle contacts the battery box or some other part of the
airframe. There will be a big flash as a couple of thousand amps
flows in the wrench handle. A hole will appear in the aluminum
airframe or battery box where the wrench contacted it . This is bad
but what happens next is worse. The flash is next to a battery vent
cap and the O2 and H2 gas inside the battery ignite and blow the top
off of the battery spraying battery acid in your eyes and all over
the airplane.
Need I say more?
John

John_F wrote:
Well lets say you are a hot shot mechanic and disconnect the hot side
of the battery first with your handy dandy metallic wrench. Some
sweet young thing walks by and distracts you for an instant and the
wrench handle contacts the battery box or some other part of the
airframe. There will be a big flash as a couple of thousand amps
flows in the wrench handle. A hole will appear in the aluminum
airframe or battery box where the wrench contacted it . This is bad
but what happens next is worse. The flash is next to a battery vent
cap and the O2 and H2 gas inside the battery ignite and blow the top
off of the battery spraying battery acid in your eyes and all over
the airplane.
Need I say more?
John

On Mon, 06 Dec 2004 16:48:03 GMT, zatatime wrote:

On Mon, 6 Dec 2004 06:15:07 +0000 (UTC), David Lesher
wrote:

Or pull the alternator [disconnect the battery ground FIRST, please..]


Why is this important? What will happen if you don't disconnect the
ground first?

Also thanks for the link on understanding the alternator!

z

It happens all the time. Most people have no appreciation for how much
energy you get out of a shorted battery.

I know of two neighbors in the block who've blown up their car batteries.

I taught generator (as in skid mounted power) repair for a while in the
Army and got real tired of hauling nimrods who ignored the warning
down to the aid station and filling out accident paperwork.

A good friend who knows better but thought he could get away with a quickie
on his motorcyle welded his watch band across the battery and frame and got
a 3rd degree burn half way around his wrist.

A guy my wife works with was out of work for a week to heal after a "simple"
fix on his car without disconnecting the battery.

While I was working in an avionics shop, a newbie melted a hole in the cowl
of a Cessna. Battery didn't blow on that one but the hole really ****ed off
the owners (shop and A/C).

I've got more if anyone isn't convinced by now.

--
Jim Pennino

Remove -spam-sux to reply.

On Tue, 07 Dec 2004 00:52:03 GMT, (John_F) wrote:

Well lets say you are a hot shot mechanic and disconnect the hot side
of the battery first with your handy dandy metallic wrench. Some
sweet young thing walks by and distracts you for an instant and the
wrench handle contacts the battery box or some other part of the
airframe. There will be a big flash as a couple of thousand amps
flows in the wrench handle. A hole will appear in the aluminum
airframe or battery box where the wrench contacted it . This is bad
but what happens next is worse. The flash is next to a battery vent
cap and the O2 and H2 gas inside the battery ignite and blow the top
off of the battery spraying battery acid in your eyes and all over
the airplane.
Need I say more?
John


Thanks for the explanation. I was confused and thought you meant to
disconnect the ground from the alternator before the field. I do
understand to disconnect the battery negative first and reconnect it
last for the reasons you've given. I've been that 'hot shot' before
and startled the hell out of me! Luckily nothing serious happened,
just a little black spot on the battery box.

If I may indulge you, when disconnecting/reconnecting the terminals at
the alternator, is there any particular order, or precautions one
should take?

TIA.
z

On Tue, 07 Dec 2004 01:00:19 GMT, "Jon Woellhaf"
wrote:

All of which is much less likely if you've disconnected the ground first.
That way, you'll have to hit both battery terminals simultaneously to
experience John's scenario.

Jon

Yep. Got it. I missed the point and thought he was talking about the
alternator, not the battery.

Thanks for the reply.
z