How long on an alternator?

The alternator on my 180hp Lycoming is putting out a whine in my
headset. My a/p recommends a replacement. It's 7 yrs (about 600 hrs)
old. Is this reasonable time frame for an alternator to last?

On Nov 27, 10:17 pm, skym wrote:
The alternator on my 180hp Lycoming is putting out a whine in my
headset. My a/p recommends a replacement. It's 7 yrs (about 600 hrs)
old. Is this reasonable time frame for an alternator to last?

Did the alternator whine begin or get much worse recently, or was it
always there? If it got worse suddenly, then you have lost a diode in
the rectifier stack (six diodes) inside the alternator, and yes it
needs to be rebuilt. Frequently, what happens is that a solder
connection between the stator wires and one of the diodes comes apart
due to heat and vibration, but the diodes are actually ok.

If the alternator whine is long standing, then unlikely that o/h the
alternator will cure that. The consequence of a partially failed
alternator is a less-than-fully charged battery, with cranking
problems, especially in cold weather. With worn brushes, or a
partially failed diode stack, the alternator still sort-of works at
light bus loads, but when you turn on most of the big loads (Nav/
Landing/Taxi/Pitot heat), the alternator isn't keeping up with the
load current, so your battery is discharging. Under day VFR (light
load), it may produce just enough current to sort-of work.

My Ford alternators in my Cessnas have lasted more than 600hrs. My
buddies with Mopar alternators in their Pipers aren't so lucky...

This topic has come up lots of times, so Google Groups search in
rec.aviation.owning back about 5 years.

On Nov 27, 10:17 pm, skym wrote:

The alternator on my 180hp Lycoming is putting out a whine in my
headset. My a/p recommends a replacement. It's 7 yrs (about 600 hrs)
old. Is this reasonable time frame for an alternator to last?

I hope you're not using the FBO on the field to make that determination.
Over here on the westend we have a great mechanic who just retired
from Corporate Air last December. He works out of his T Hangar on the
back side of mine, you left the note there last year.

My Ford alternators in my Cessnas have lasted more than 600hrs. My
buddies with Mopar alternators in their Pipers aren't so lucky...

I'm currently flying a Piper with 900 hours on the alternator and it's
still working fine.

BTW, the Piper service manual contains the procedure for replacing the
bearings, brushes and diodes inside the Chrysler alternator, so an A&P
can legally perform a field overhaul on them.

My Ford alternators in my Cessnas have lasted more than 600hrs. My
buddies with Mopar alternators in their Pipers aren't so lucky...

I'm currently flying a Piper with 900 hours on the alternator and it's
still working fine.

Same here.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

skym wrote:
The alternator on my 180hp Lycoming is putting out a whine in my
headset. My a/p recommends a replacement. It's 7 yrs (about 600 hrs)
old. Is this reasonable time frame for an alternator to last?

I got over 1000 hrs out of the last Chrysler alternator on my Cherokee.
The current one (also a Chrysler rebuild) has been going strong for the last
400 hrs.

When the current one finally dies, I'm planning on replacing it with a
brand new Plane Power alternator. While my personal experience with the old
rebuilds has been OK, I've been hearing a lot of horror stories over the
past few years about bad rebuilds out of the box. I know a couple of A&P/IAs
that are running all rebuilt alternators on the bench before installing them,
because the failure rates have been so high.

John Galban=====N4BQ (PA28-180)

--
Message posted via AviationKB.com
http://www.aviationkb.com/Uwe/Forums...ation/200711/1

On Nov 28, 2:03 pm, "JGalban via AviationKB.com" u32749@uwe wrote:
skym wrote:
The alternator on my 180hp Lycoming is putting out a whine in my
headset. My a/p recommends a replacement. It's 7 yrs (about 600 hrs)
old. Is this reasonable time frame for an alternator to last?

Could be diodes, more likely a failed filter. There's probably
one in the output line, and might be another in the field circuit.
Back EMF from the rotor can cause whine, hence the field capacitor. In
older airplanes, whine can be caused by poor grounds causing
electrical ground loops, where instead of grounding and passing
through the airframe, the current, looking for a lower resistance,
travels through stuff it has no business in, like radios or intercoms.
Strobes often do that; the ground current will find difficulty running
through old, dirty riveted seams and might run instead through antenna
or intercom shielding, feeding a whine into the airplane's radios.

I've been hearing a lot of horror stories over the
past few years about bad rebuilds out of the box. I know a couple of A&P/IAs
that are running all rebuilt alternators on the bench before installing them,
because the failure rates have been so high.

We've had two Kelly Aerospace rebuilds give trouble in the
last few months. The rebuilder puts too much grease in the rear
bearing so it gets flung out and ends up on the slip rings, where the
brushes smear it around and cook it into a resistive coating,
whereupon the output falls off.

Dan

On Nov 28, 5:47 pm, wrote:
Could be diodes, more likely a failed filter. There's probably
one in the output line, and might be another in the field circuit.

The filter in the output line (usually a 0.1uF to 2uF Hypass Coaxial
capacitor) is there for ONE reason only. It is an RF bypass capacitor
to keep alternator brush noise out of the ADF an/or Loran at 200kHz
and above. It does NOTHING to filter the alternator ripple at the
alternator rotation frequency of about 1kHz, never did, never will.
The minimum amount of capacitance that would have be paralleled with
the alternator output that would actually reduce the ripple would be
50,000uF. However the effective series resistance of a large
electrolytic capacitor is so high that such a capacitor is not
particularly effective at reducing the ripple. It is up to the
aircraft battery to act as the filter for alternator ripple; it is
very effective at reducing the total bus voltage ripple to less than
100mV. The large potted HYSONIC type filters are also only for
filtering ADF and higher frequencies.

Back EMF from the rotor can cause whine, hence the field capacitor.

You are probably referring to the INTERAV STCed alternator conversion.
For whatever reason, the original developer of this STC put a
100,000uF electrolytic capacitor to filter the source of the field
voltage upstream of the Voltage Regulator. This capacitor does NOTHING
to reduce the ripple content of the automotive Motorola alternator.
There were tens of Millions of this exact same alternator installed in
automobiles in the 1960 and 1970s without this capacitor. This STC was
poorly conceived; the large capacitor produces no benefit to the
operation of the alternator, but it introduced a single-point failure
mode when that large electrolytic was subjected to the hight
temperatures (for an electrolytic) under the cowling. If you call the
present STC holder, they admit this, but don't want to spend the money
to get the STC re-certified by the FAA if they remove it...

Alternator whine heard in aircraft avionics audio has nothing to do
with "filtering" at the alternator. It has everything to do with how
the avionics wiring harnesses were fabricated and installed. If the
avionics wiring is properly done using a "single-point-grounding", and
to a lesser extent, proper shielding, there is no detectable
alternator whine or strobe squeal, filters or not!

"mikem" wrote a lot of good stuff about aircraft alternators.
....
Alternator whine heard in aircraft avionics audio has nothing to do
with "filtering" at the alternator. It has everything to do with how
the avionics wiring harnesses were fabricated and installed. If the
avionics wiring is properly done using a "single-point-grounding", and
to a lesser extent, proper shielding, there is no detectable
alternator whine or strobe squeal, filters or not!

But what do you know? You only have a PhD in electrical engineering. g

Thanks for the info.

Jon

Thanks to all for your replies. Sounds like a diode problem.
Newps.. I think I know who you mean; I recently spoke with him.