How long on an alternator?

[skym]

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?

[mikem]

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.

[Newps]

> 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.

[[email protected]]

> 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.

[Jay Honeck]

> > 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"

[JGalban via AviationKB.com]

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.aspx/aviation/200711/1

[[email protected]]

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

[mikem]

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!

[Jon Woellhaf]

"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

[skym]

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

[Mike Spera]

wrote:

>>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.

The Chrysler rebuild I got from the engine overhauler lasted about 700
hours before the bearings went out (hey, is the inside SUPPOSED to look
scraped clean?). The replacement went about 200 hours before the front
bushing started to work out. I gently tapped it back in with the back of
a large socket. Don't know if it will stay.

When you start with a piece of crap, what do you expect?

Good Luck,
Mike

[[email protected]]

On Nov 29, 10:26 am, mikem > wrote:
> 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!

Thanks for the corrections. It'll make it easier to find that
pesky whine when it shows up. The avionics single-point grounding IS
related to the ground-loop phenomenon, though, right?

Dan

[mikem]

On Dec 2, 6:25 pm, wrote:
> ...

> Thanks for the corrections. It'll make it easier to find that
> pesky whine when it shows up. The avionics single-point grounding IS
> related to the ground-loop phenomenon, though, right?
>
> Dan

Right Dan,

all common aircraft avionics, audio panels, panel-mounted intercoms,
internally tie their ground pin(s) to the metal box they are housed
in. In other words, if you use an Ohmmeter to measure the resistance
from any ground pin to the box, you see a dead short. When that box is
slid into a tray, or mounted to the airframe, the box makes electrical
contact to the tray or local airframe structure.

To eliminate "ground loops" induced into the audio wiring by high
current paths circulating in the airframe structure (particularly
alternator & strobe ground currents), it is necessary to define a
"single-point-audio-ground-mecca" within inches of the center-stack in
the aircraft panel. Any item mounted distal to the center stack (like
headphone/mic jacks, CD/Ipod players, speaker, Garmin 496 XM radio)
that connects into the audio system must be locally electrically
isolated from airframe ground, and a separate ground wire has to be
carried back to the "audio ground mecca".

In troublesome cases where some audio source (like a Marker Beacon
receiver) is mounted a long way from the center-stack, it might be
necessary to use an audio transformer to break the ground loop. Other-
non audio producing avionics items like auto-pilots, gyros,
transponders, should not be tied to the "audio ground mecca"; but
should have a separate grounding point some distance from the center
stack area.

When the audio system in an aircraft is wired this way it eliminates
the alternator whine, strobe squeal, beacon thump, and other annoying
noises from the headphones. You can really enjoy good stereo music
played through ANR headsets. Unfortunately, most of our 1950s through
1980s aircraft did not come wired that way from the factory, and most
after-market avionics installers screw things up even worse. Fixing
aircraft audio wiring screw-ups is a hobby of mine.

One downside is that if you lose a diode in the alternator, you dont
"hear" the increased ripple; you only notice it when the battery
becomes discharged and that manifests as slow cranking (or on a
voltmeter). That happened in my Skylane.

MikeM

[Michelle[_1_]]

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?
1200 hours and still going strong.


Is there a filter on the batt terminal? is it still connected? Is the
field wire shielded? Is the alternator getting plenty of air? Check the
engine to airframe ground. Poor grounds are a big problem...

[Mike Gilmour]

"mikem" > wrote in message
...
> 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!
>

Cessna has a 5.72 microfarad capacitor filter available (part number
S1915-1) to combat alternator noise but I'd also suspect this would be
ineffective. Would the loss of one diode from the alternator rectifying
plate of (generally) six be immediately obvious if the battery was in good
and well charged condition i.e. acting as a very large value smoothing
capacitor. The loss of one phase would indicate reduced current on the
alternator ammeter but would that be enough to maintain battery charge
equilbrium in general circumstances?

Mike

[mikem]

On Dec 3, 8:06 am, "Mike Gilmour" > wrote:
> "mikem" > wrote in message
> >...
> > 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!
>
> Cessna has a 5.72 microfarad capacitor filter available (part number
> S1915-1) to combat alternator noise but I'd also suspect this would be
> ineffective.

This is the ADF/Loran RFI filter I was talking about earlier. Lonestar
makes it. If you read their advertising, they try to perpetuate the
myth that putting one of these will reduce alternator whine heard in
headphones. This is true ONLY if the alternator whine is coming from
the ADF receiver (i.e. it is being received and demodulated by the ADF
receiver). It would only be heard if the ADF switch on the audio panel
is selected. As more an more aircraft owners dump their ADFs and
Lorans, then having the RFI filter on the alternator becomes
unimportant.

> Would the loss of one diode from the alternator rectifying
> plate of (generally) six be immediately obvious if the battery was in good
> and well charged condition i.e. acting as a very large value smoothing
> capacitor.

With a good alternator, if you hear the slightest amount of alternator
whine in your headset with radios silent and intercom squelched, then
after the alternator loses a diode, the noise will change character,
and get a lot louder. In my rewired audio system, I had no detectable
alternator whine to begin with, so when the alternator went west, I
got no audible que. The discharge indication on the ammeter, and the
bus voltage told the story. I have since installed an EI UBG16, and
have allocated one of the channels to Bus Voltage. I set two alarms
on that channel; <12.8V and >14.8V, which instantly alerts me of any
anomaly in the charging system.

> The loss of one phase would indicate reduced current on the
> alternator ammeter but would that be enough to maintain battery charge
> equilbrium in general circumstances?

Only during day VFR. At night or during IMC, an alternator with a
partially failed diode stack will not keep up with the load, and a
Cessna zero-center ammeter will show a slight continuous discharge. A
Piper Loadmeter just shows less alternator current, but doesn't
indicate that your battery will eventually run out of charge, unless
you also have a voltmeter. I prefer the Cessna zero-center ammeter
for this reason.

MikeM

[mikem]

On Dec 3, 5:55 am, Michelle >
wrote:

> Is there a filter on the batt terminal? is it still connected? Is the
> field wire shielded?

Not relevant to the OP's problem. He wasn't complaining that he was
hearing his alternator on his ADF :-)

> Is the alternator getting plenty of air?

Lack of cooling and vibration is the reason that most alternator diode
stacks fail.

> Check the engine to airframe ground. Poor grounds are a big problem...

If the starter motor cranks ok, the voltage drop due to resistance
between the engine and the airframe cannot be the problem. The starter
current is about 250A, while the peak alternator current is only about
50A. Resistance between the frame of the alternator and the engine
crankcase can result in less than optimal charging, but usually does
not cause an increase in alternator whine heard in the headset.

MikeM

[[email protected]]

> This is the ADF/Loran RFI filter I was talking about earlier. Lonestar
> makes it. If you read their advertising, they try to perpetuate the
> myth that putting one of these will reduce alternator whine heard in
> headphones. This is true ONLY if the alternator whine is coming from
> the ADF receiver (i.e. it is being received and demodulated by the ADF
> receiver). It would only be heard if the ADF switch on the audio panel
> is selected. As more an more aircraft owners dump their ADFs and
> Lorans, then having the RFI filter on the alternator becomes
> unimportant.
>

The Lonestar 'Eliminator' filter (http://www.lonestaraviation.com/
eliminator.htm) that goes in line with the power feed to the avionics
does do a great job of stopping alternator whine that comes riding
along the power wire into the radio/intercom/whatever. I used to fly
an old Cherokee that had the little Terra NAV/COM radios and the
alternator whine was terrible. The owner had one of these Lonestar
filters installed into the power feed to the Terra and intercom, and
it stopped the whine completely.

$90 is a lot of money for a simple coil of wire and a capacitor
sealed up inside a metal can, but it is PMA'd. Radio Shack used to
sell something similar for about $10 for use with CB radios and
stereos, but I haven't seem one at an RS store in about a decade.

[Darrel Toepfer]

wrote:

> $90 is a lot of money for a simple coil of wire and a capacitor
> sealed up inside a metal can, but it is PMA'd. Radio Shack used to
> sell something similar for about $10 for use with CB radios and
> stereos, but I haven't seem one at an RS store in about a decade.

5 amp $12
http://www.valcoelectronics.com/Merchant2/merchant.mv?
Screen=PROD&Store_Code=VE&Product_Code=AS-PLNE5H

6 amp single stage for $13
http://www.valcoelectronics.com/Merchant2/merchant.mv?
Screen=PROD&Store_Code=VE&Product_Code=ES013

10 amp $14
http://www.valcoelectronics.com/Merchant2/merchant.mv?
Screen=PROD&Store_Code=VE&Product_Code=AS-PLNE10H

35 amp $10
http://www.valcoelectronics.com/Merchant2/merchant.mv?
Screen=PROD&Store_Code=VE&Product_Code=NS50

[Mike Gilmour]

"mikem" > wrote in message
...
> On Dec 3, 8:06 am, "Mike Gilmour" > wrote:
>> "mikem" > wrote in message
>> >...
>> > 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!
>>
>> Cessna has a 5.72 microfarad capacitor filter available (part number
>> S1915-1) to combat alternator noise but I'd also suspect this would be
>> ineffective.
>
> This is the ADF/Loran RFI filter I was talking about earlier. Lonestar
> makes it. If you read their advertising, they try to perpetuate the
> myth that putting one of these will reduce alternator whine heard in
> headphones. This is true ONLY if the alternator whine is coming from
> the ADF receiver (i.e. it is being received and demodulated by the ADF
> receiver). It would only be heard if the ADF switch on the audio panel
> is selected. As more an more aircraft owners dump their ADFs and
> Lorans, then having the RFI filter on the alternator becomes
> unimportant.
>
>> Would the loss of one diode from the alternator rectifying
>> plate of (generally) six be immediately obvious if the battery was in
>> good
>> and well charged condition i.e. acting as a very large value smoothing
>> capacitor.
>
> With a good alternator, if you hear the slightest amount of alternator
> whine in your headset with radios silent and intercom squelched, then
> after the alternator loses a diode, the noise will change character,
> and get a lot louder. In my rewired audio system, I had no detectable
> alternator whine to begin with, so when the alternator went west, I
> got no audible que. The discharge indication on the ammeter, and the
> bus voltage told the story. I have since installed an EI UBG16, and
> have allocated one of the channels to Bus Voltage. I set two alarms
> on that channel; <12.8V and >14.8V, which instantly alerts me of any
> anomaly in the charging system.
>
>> The loss of one phase would indicate reduced current on the
>> alternator ammeter but would that be enough to maintain battery charge
>> equilbrium in general circumstances?
>
> Only during day VFR. At night or during IMC, an alternator with a
> partially failed diode stack will not keep up with the load, and a
> Cessna zero-center ammeter will show a slight continuous discharge. A
> Piper Loadmeter just shows less alternator current, but doesn't
> indicate that your battery will eventually run out of charge, unless
> you also have a voltmeter. I prefer the Cessna zero-center ammeter
> for this reason.
>
> MikeM


An EI UBG16 and a zero-centre ammeter would also be good belt & braces
monitoring with the advantage of data logging. It would be interesting to
know the minimum supply voltage the UBG16 unit itself operates at? The unit
should have sufficient storage or an internal battery system to continue
logging a number of lengthy low voltage anomalies. A worst case scenario
perhaps but its reassuring to know of its minumum supply specification e.g.
does the display shut down at low voltage but data storage continue.


Mike

[mikem]

On Dec 3, 10:34 am, wrote:

> The Lonestar 'Eliminator' filter (http://www.lonestaraviation.com/
> eliminator.htm) that goes in line with the power feed to the avionics
> does do a great job of stopping alternator whine that comes riding
> along the power wire into the radio/intercom/whatever. I used to fly
> an old Cherokee that had the little Terra NAV/COM radios and the
> alternator whine was terrible. The owner had one of these Lonestar
> filters installed into the power feed to the Terra and intercom, and
> it stopped the whine completely.

My Piper Pacer had one of these filters in it when I first got it. It
had just a single ValCom, and a Sigtronics SPA400 intercom.There was
so much alternator whine and strobe squeal that it almost drove me
nuts. I thought the filter had failed so I took it out. That made
absolutely NO difference. I had to unground (isolate) all ten mic/
headphone jacks, the cabin speaker, the PTT switch on the yoke, as
well as rewiring the SPA400 and moving some other grounds to separate
them from the avionics grounds. That got rid of 95% of the whine/
squeal. Reconnecting the filter got rid of about half of the remaining
noise.

Subsequently, I removed the ValCom and replaced it with a Narco Mark
12D. That got rid of all the remaining noise, with or without the
filter hooked up, so I removed it. My conclusion is that the filter is
not effective in curing the overall problem, which in this case was a
ground loop. The ValCom obviously was worse at rejecting ripple on its
supply line than the Narco that replaced it. It could be that Terra is
also sensitive to ripple.

I recently installed a PSE PM3000 stereo intercom in a friend's 172.
PSE claims right on their PM3000 spec sheet that the attenuation from
the power input to the audio output is a minimum of -65db. Since there
is about 100mV of ripple on the bus of the typical aircraft, that
would mean that the amount of ripple that would appear on the audio
out would be about 56uV. Since the normal listening level at the
output of the intercom is about 2vp-p, the noise would actually be
90db below 2V. Almost any IC chip audio amp made has a power supply
rejection ratio (PSRR) of >60db, so the designer of any avionics that
is sensitive to power supply ripple (and would benefit from the
Lonestar filter) has to be a total idiot. I know from experience that
COMS like a KX170, KX155, Mark12D, SL30, SL40, audio panels like the
PSE, King KMA20/24/26, intercoms like the PSE PM1000 & PM3000 do NOT
need the Lonestar filter.

MikeM

[mikem]

On Dec 3, 5:38 pm, "Mike Gilmour" > wrote:

> An EI UBG16 and a zero-centre ammeter would also be good belt & braces
> monitoring with the advantage of data logging. It would be interesting to
> know the minimum supply voltage the UBG16 unit itself operates at? The unit
> should have sufficient storage or an internal battery system to continue
> logging a number of lengthy low voltage anomalies. A worst case scenario
> perhaps but its reassuring to know of its minumum supply specification e.g.
> does the display shut down at low voltage but data storage continue.

Per the UBG16 Installation Manual (downloadable at www.buy-ei.com),
the UBG16 operates on 10.5 to 35V. The MUX8 data logger module
requires 7.5V to 35V. Since the UBG16 sends RS232 to the MUX8, I
suspect that the data stream from the UBG16 will quit first.

If I have an inflight alternator failure, I will try to be on the
ground long before the battery discharges below 12.0V. Since I know
within seconds that the alternator trips off line, by shedding loads,
I should easily have 30 to 45min of battery life to run essentials,
like Gyros, GPS, NAV, COM and Transponder. I do a battery capacity
tests as part of the annual inspection. I replace nominally 25AH
batteries if their capacity degrades below 18AH. This test is
described in the "continuing airworthiness" section of both Gill's and
Concorde's Battery Manual.