OK, Thinking-Cap Time...

[Jay Honeck]

Of course, we have a new squawk shortly after coming out of the shop.
Perhaps someone here can point me in the right direction?

Here's the scenario with our 1974 Piper Cherokee Pathfinder, with a 530
hour, normally aspirated Lycoming O-540-B4B5 engine:

1) Flying to Janesville, WI today. Extremely cold -- around 15 degrees
Fahrenheit on the surface, near zero at altitude. The first real cold snap
of the year.

2) In steady-state flight, both of us hear a "woo--woo--woo..." softly in
the headphones. It sounds just like strobes that aren't grounded properly.

3) The noise slows down -- or speeds up -- in synch with the prop RPM. At
2300 RPM, it's going a bit faster than once per second -- maybe around three
times every two seconds.

4) I switch our digital voltage/amperage meter to AMPs, and watch as it
oscillates in time with the noise. It's alternating from 5 amps to 10-11
amps, in time with the "woo--woo--woo"... Voltage appears to be pretty
steady at around 13.8-ish volts.

5) Adding load to the system (landing lights, fuel pump, etc.) makes the
noise louder. Adding load to the system and then suddenly turning
everything off makes the noise and amperage oscillation go away -- for about
30 seconds. It then returns.

6) Turning the alternator side of the split master switch ALSO makes the
noise go away. It sometimes stays away when I turn the alternator back on.
Sometimes it doesn't.

7) The battery is new this past summer.

So, we've got a noise and amperage indication that can be corrected by
adding load to the system -- and then suddenly taking it away. The noise
is also fixed -- sometimes -- by cycling the alternator off and on.

The service last week was having the impulse couplings serviced (per service
bulletin), so electrical things have been tinkered with since our last
flight. (This is ALWAYS when some new squawk seems to crop up.)

Any ideas? Loose ground wire somewhere? Alternator failing? Any and all
input is welcomed!

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

[George Patterson]

Jay Honeck wrote:
> Of course, we have a new squawk shortly after coming out of the shop.
> Perhaps someone here can point me in the right direction?

Alternator problem. Possibly a filter, but my guess is a diode is going bad.

> 3) The noise slows down -- or speeds up -- in synch with the prop RPM. At
> 2300 RPM, it's going a bit faster than once per second -- maybe around three
> times every two seconds.

Alternator speed depends on engine speed.

> 5) Adding load to the system (landing lights, fuel pump, etc.) makes the
> noise louder. Adding load to the system and then suddenly turning
> everything off makes the noise and amperage oscillation go away -- for about
> 30 seconds. It then returns.

Adding load makes the alternator work harder. Cutting it all out lets it loaf
until the battery charge drops a bit, then the alternator has to work again.

George Patterson
If a tank is out of ammunition, what you have is a sixty ton portable
radio.

[Jim Burns]

I'd say George is dead on. I also thought filter, but the fact that the
amps oscillate makes me think diode. I've never heard of a bad filter
causing an ammeter oscillation, the filters that have failed for me just
complain loudly.
Jim

[nrp]

Could it be a very loose alternator belt ? The symptoms don't all jib
though.

[Jim Burns]

See: http://www.sacskyranch.com/altnoise.htm

Jim

[Michelle P]

I third the thought. I have a capacitor filter across the output of the
alternator and ground. I have also cooked an alternator in the summer .
The fan on the back was not enough forced air for a high load when it is
hot. I added a blast tube form the front of the cowling to the "Blast
adapter" on the back on the Alternator. The hole in my cowling just
below the engine air intake is for the alternator. Works great. No more
over heating problems.
Michelle

George Patterson wrote:

> Jay Honeck wrote:
>
>> Of course, we have a new squawk shortly after coming out of the shop.
>> Perhaps someone here can point me in the right direction?
>
>
> Alternator problem. Possibly a filter, but my guess is a diode is
> going bad.
>
>> 3) The noise slows down -- or speeds up -- in synch with the prop
>> RPM. At 2300 RPM, it's going a bit faster than once per second --
>> maybe around three times every two seconds.
>
>
> Alternator speed depends on engine speed.
>
>> 5) Adding load to the system (landing lights, fuel pump, etc.) makes
>> the noise louder. Adding load to the system and then suddenly
>> turning everything off makes the noise and amperage oscillation go
>> away -- for about 30 seconds. It then returns.
>
>
> Adding load makes the alternator work harder. Cutting it all out lets
> it loaf until the battery charge drops a bit, then the alternator has
> to work again.
>
> George Patterson
> If a tank is out of ammunition, what you have is a sixty ton
> portable
> radio.

[Mike Spera]

>
> 2) In steady-state flight, both of us hear a "woo--woo--woo..." softly in
> the headphones. It sounds just like strobes that aren't grounded properly.
>
> 3) The noise slows down -- or speeds up -- in synch with the prop RPM. At
> 2300 RPM, it's going a bit faster than once per second -- maybe around three
> times every two seconds.
>
> 4) I switch our digital voltage/amperage meter to AMPs, and watch as it
> oscillates in time with the noise. It's alternating from 5 amps to 10-11
> amps, in time with the "woo--woo--woo"... Voltage appears to be pretty
> steady at around 13.8-ish volts.
>

Jay,

Is this not the "Cherokee oscillating Ammeter" thing? Mine has it. Exact
same symptoms. Had it for 11 years and 4 different alternators. Either
the split master switch (alternator side) or the alternator breaker
having a high resistance connection (either the wires or the
switch/breaker itself).

Google it. You should see lots of hits. A common problem if I recall.

Mike

[Jay Honeck]

> See: http://www.sacskyranch.com/altnoise.htm

Awesome source -- thanks!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jay Honeck]

> Is this not the "Cherokee oscillating Ammeter" thing? Mine has it. Exact
> same symptoms. Had it for 11 years and 4 different alternators. Either the
> split master switch (alternator side) or the alternator breaker having a
> high resistance connection (either the wires or the switch/breaker
> itself).
>
> Google it. You should see lots of hits. A common problem if I recall.

It may be -- but it just started happening in mine. *Something* had to
change, and the fact that my mechanic was digging around in the magnetos
last week seems to point to the all-to-common "mechanic-induced" squawk.

Or, it could be the sudden, severe cold? Or, it could be coincidence.

Next nice day I'm going to de-cowl the engine and tighten all electrical
connections. That has cured other electrical gremlins for us...and it's
cheap!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[nrp]

Jay - If you get desperate, you might be able to create this problem on
the ground using a hand held or jury rigged electric motor to spin the
alternator rather than having to run the engine. This would allow
better diagnostic capability using an oscilloscope.

However, if the problem only occurs only at higher amperage loads, a
fractional hp electric motor won't be able to spin the alternator.
Likewise the RPM may be a problem. Alternators spin pretty fast at
cruise - like over 10,000 rpm.

[George Patterson]

nrp wrote:
> Jay - If you get desperate, you might be able to create this problem on
> the ground using a hand held or jury rigged electric motor to spin the
> alternator rather than having to run the engine. This would allow
> better diagnostic capability using an oscilloscope.

If you try this, keep a fan blowing on the alternator. Even in cold
temperatures, it will need cooling air.

George Patterson
If a tank is out of ammunition, what you have is a sixty ton portable
radio.

[Jay Masino]

Jay Honeck > wrote:
> last week seems to point to the all-to-common "mechanic-induced" squawk.

It's not just mechanics. Any good troubleshooter knows you always look
"where the human being was last".



--
__!__
Jay and Teresa Masino ___(_)___
http://www2.ari.net/jmasino ! ! !
http://www.OceanCityAirport.com
http://www.oc-Adolfos.com

[Ross Richardson]

I would check all the grounds in the system. That can cause this
problem. Along with a bad alternator switch. It causes the VR to not
work properly. I had to bread each connection, clean it, then re-do it.


-------------
Regards, Ross
C-172F 180HP
KSWI


Jay Honeck wrote:
> Of course, we have a new squawk shortly after coming out of the shop.
> Perhaps someone here can point me in the right direction?
>
> Here's the scenario with our 1974 Piper Cherokee Pathfinder, with a 530
> hour, normally aspirated Lycoming O-540-B4B5 engine:
>
> 1) Flying to Janesville, WI today. Extremely cold -- around 15 degrees
> Fahrenheit on the surface, near zero at altitude. The first real cold snap
> of the year.
>
> 2) In steady-state flight, both of us hear a "woo--woo--woo..." softly in
> the headphones. It sounds just like strobes that aren't grounded properly.
>
> 3) The noise slows down -- or speeds up -- in synch with the prop RPM. At
> 2300 RPM, it's going a bit faster than once per second -- maybe around three
> times every two seconds.
>
> 4) I switch our digital voltage/amperage meter to AMPs, and watch as it
> oscillates in time with the noise. It's alternating from 5 amps to 10-11
> amps, in time with the "woo--woo--woo"... Voltage appears to be pretty
> steady at around 13.8-ish volts.
>
> 5) Adding load to the system (landing lights, fuel pump, etc.) makes the
> noise louder. Adding load to the system and then suddenly turning
> everything off makes the noise and amperage oscillation go away -- for about
> 30 seconds. It then returns.
>
> 6) Turning the alternator side of the split master switch ALSO makes the
> noise go away. It sometimes stays away when I turn the alternator back on.
> Sometimes it doesn't.
>
> 7) The battery is new this past summer.
>
> So, we've got a noise and amperage indication that can be corrected by
> adding load to the system -- and then suddenly taking it away. The noise
> is also fixed -- sometimes -- by cycling the alternator off and on.
>
> The service last week was having the impulse couplings serviced (per service
> bulletin), so electrical things have been tinkered with since our last
> flight. (This is ALWAYS when some new squawk seems to crop up.)
>
> Any ideas? Loose ground wire somewhere? Alternator failing? Any and all
> input is welcomed!
>
> Thanks!

[Ross Richardson]

OK, lets make that BREAK instead of bread.


-------------
Regards, Ross
C-172F 180HP
KSWI


Ross Richardson wrote:
> I would check all the grounds in the system. That can cause this
> problem. Along with a bad alternator switch. It causes the VR to not
> work properly. I had to bread each connection, clean it, then re-do it.
>
>
> -------------
> Regards, Ross
> C-172F 180HP
> KSWI
>
>
> Jay Honeck wrote:
>
>> Of course, we have a new squawk shortly after coming out of the shop.
>> Perhaps someone here can point me in the right direction?
>>
>> Here's the scenario with our 1974 Piper Cherokee Pathfinder, with a
>> 530 hour, normally aspirated Lycoming O-540-B4B5 engine:
>>
>> 1) Flying to Janesville, WI today. Extremely cold -- around 15
>> degrees Fahrenheit on the surface, near zero at altitude. The first
>> real cold snap of the year.
>>
>> 2) In steady-state flight, both of us hear a "woo--woo--woo..." softly
>> in the headphones. It sounds just like strobes that aren't grounded
>> properly.
>>
>> 3) The noise slows down -- or speeds up -- in synch with the prop
>> RPM. At 2300 RPM, it's going a bit faster than once per second --
>> maybe around three times every two seconds.
>>
>> 4) I switch our digital voltage/amperage meter to AMPs, and watch as
>> it oscillates in time with the noise. It's alternating from 5 amps to
>> 10-11 amps, in time with the "woo--woo--woo"... Voltage appears to
>> be pretty steady at around 13.8-ish volts.
>>
>> 5) Adding load to the system (landing lights, fuel pump, etc.) makes
>> the noise louder. Adding load to the system and then suddenly turning
>> everything off makes the noise and amperage oscillation go away -- for
>> about 30 seconds. It then returns.
>>
>> 6) Turning the alternator side of the split master switch ALSO makes
>> the noise go away. It sometimes stays away when I turn the
>> alternator back on. Sometimes it doesn't.
>>
>> 7) The battery is new this past summer.
>>
>> So, we've got a noise and amperage indication that can be corrected by
>> adding load to the system -- and then suddenly taking it away. The
>> noise is also fixed -- sometimes -- by cycling the alternator off and on.
>>
>> The service last week was having the impulse couplings serviced (per
>> service bulletin), so electrical things have been tinkered with since
>> our last flight. (This is ALWAYS when some new squawk seems to crop up.)
>>
>> Any ideas? Loose ground wire somewhere? Alternator failing? Any
>> and all input is welcomed!
>>
>> Thanks!

[Dick Meade]

Does it go away when you turn off the beacon?

Ammeter swings and a similar noise in my plane are due to the beacon's
flasher.

[john smith]

> OK, lets make that BREAK instead of bread.

So now we are breaking bread over our engines to fix problems?

[Montblack]

>>> OK, lets make that BREAK instead of bread.

>> So now we are breaking bread over our engines to fix problems?

("Darrel Toepfer" wrote)
> Is he in a jam or just buttering it over?


What a crumby thing to say :-)


Montwhitebread

[Jim Burns]

Hope the alternator itself isn't toast!
Jim

"Montblack" > wrote in message
...
> >>> OK, lets make that BREAK instead of bread.
>
> >> So now we are breaking bread over our engines to fix problems?
>
> ("Darrel Toepfer" wrote)
> > Is he in a jam or just buttering it over?
>
>
> What a crumby thing to say :-)
>
>
> Montwhitebread

[Montblack]

("Jim Burns" wrote)
> Hope the alternator itself isn't toast!


That's a half-baked assumption.

Like those Capital One ads ...No, No, No.
Any way you slice it, it's always the ground.

....cheaper that way. <g>


Montblack

[Ross Richardson]

Dang, I should have read it before I published this....


-------------
Regards, Ross
C-172F 180HP
KSWI


john smith wrote:
>>OK, lets make that BREAK instead of bread.
>
>
> So now we are breaking bread over our engines to fix problems?

[john smith]

> ("Jim Burns" wrote)
> > Hope the alternator itself isn't toast!

"Montblack" > wrote:
> That's a half-baked assumption.
> Like those Capital One ads ...No, No, No.
> Any way you slice it, it's always the ground.
> ...cheaper that way. <g>

Just be careful not to fry it.

[Jim Burns]

Oh, now you're talking like a man with only 1/2 a loaf! :)
Jim

"Montblack" > wrote in message
...
> ("Jim Burns" wrote)
> > Hope the alternator itself isn't toast!
>
>
> That's a half-baked assumption.
>
> Like those Capital One ads ...No, No, No.
> Any way you slice it, it's always the ground.
>
> ...cheaper that way. <g>
>
>
> Montblack

[David Lesher]

Clean all the grounds.

The alternator ones, the regulator ones, the frame to engine one...
--
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

[Montblack]

("Jim Burns" wrote)
> Oh, now you're talking like a man with only 1/2 a loaf! :)


Are you implying I'm light in the loafers?


Montblack
Loafing around the house today

[Jim Burns]

Hmm.... if the shoe fits!! lol ;)
Jim

"Montblack" > wrote in message
...
> ("Jim Burns" wrote)
> > Oh, now you're talking like a man with only 1/2 a loaf! :)
>
>
> Are you implying I'm light in the loafers?
>
>
> Montblack
> Loafing around the house today

[David Lesher]

"Jay Honeck" > writes:


>2) In steady-state flight, both of us hear a "woo--woo--woo..." softly in
>the headphones. It sounds just like strobes that aren't grounded properly.
....

>6) Turning the alternator side of the split master switch ALSO makes the
>noise go away. It sometimes stays away when I turn the alternator back on.
>Sometimes it doesn't.


After you clean all the grounds...

C) Others mention the split master. Does it feel warm at all? Since
its brothers have been found guilty before; it's a good suspect even
if stone cold.

Wonder if there is a safe way to bypass it long enough to make a
test flight. I'd say just replace it, but know that a $5 switch
like that becomes a $500 switch once annointed with FAA Holy Oil.

B) The skyranch URL sounds like the Right Stuph.

A) This does NOT sound like a blown alternator diode to me. The
'pulsing' from that is in the kiloHertz range; this sound like it's
more like 0.5 Hz.
--
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

[Jack Allison]

Jay Honeck wrote:
>>See: http://www.sacskyranch.com/altnoise.htm
>
>
> Awesome source -- thanks!
And located just down the road from me!


--
Jack Allison
PP-ASEL-IA Student
Arrow N2104T

"When once you have tasted flight, you will forever walk the Earth
with your eyes turned skyward, for there you have been, and there
you will always long to return"
- Leonardo Da Vinci

(Remove the obvious from address to reply via e-mail)

[Mike Spera]

>
> C) Others mention the split master.
>
> .stuff snipped

> I'd say just replace it, but know that a $5 switch
> like that becomes a $500 switch once annointed with FAA Holy Oil.


Actually, that split switch for Jay's plane is a fooler. I bought the
official Piper part from Des Moines Flying Service (DMFS.com) a couple
of years ago and I remember it being less than $50. Some day I actually
have to INSTALL IT!

I like the idea of the "Bypass wire" test. I could do it on the ground
because my Cherokee does this all the time.

Good Luck,
Mike

[Doodybutch]

"George Patterson" > wrote in message
news:Q%7ff.60$N44.3@trndny08...
<snip>
> Alternator problem. Possibly a filter, but my guess is a diode is going
> bad.
<snip>

Diodes are solid state devices which either work, are open (most common
failure), or are shorted out (less common failure). They don't suffer from
"going bad" or "getting weak". They either work or they don't. If they are
intermittant, it's a connection, not the diode itself.

DB
(Many years of Electronics experience)

[David Lesher]

"Doodybutch" > writes:



>Diodes are solid state devices which either work, are open (most common
>failure), or are shorted out (less common failure). They don't suffer from
>"going bad" or "getting weak". They either work or they don't. If they are
>intermittant, it's a connection, not the diode itself.


Well, maybe... I have had some larger power diodes whose *internal*
bonds would open when the diode got hot. When it cooled again, guess
what.

I also had a matrix of small-signal glass diodes that tested just
fine with an ohmmeter, but in operation.... turns out some would
"zener" when tested with the 12v that was used in the circuit.

But I really doubt that Jay's issue is alternator diodes....


--
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

[Jay Honeck]

>> > Oh, now you're talking like a man with only 1/2 a loaf! :)
>>
>> Are you implying I'm light in the loafers?

Crikey! And *I* get accused of off-topic posts!

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

[Jack Allison]

Jay Honeck wrote:

> Crikey! And *I* get accused of off-topic posts!
>
> :-)
Only by those with lesser senses of humor :-)



--
Jack Allison
PP-ASEL-IA Student
Arrow N2104T

"When once you have tasted flight, you will forever walk the Earth
with your eyes turned skyward, for there you have been, and there
you will always long to return"
- Leonardo Da Vinci

(Remove the obvious from address to reply via e-mail)

[Ray Andraka]

David Lesher wrote:


> Wonder if there is a safe way to bypass it long enough to make a
> test flight. I'd say just replace it, but know that a $5 switch
> like that becomes a $500 switch once annointed with FAA Holy Oil.
>
>

The piper split master is approximately $35 from Piper. You can
bypass the alternator field side of the switch by unscrewing the lugs
from the switch and fastening them together with a small bolt, nut and
star washer. Put the joint in an insulating sleeve to protect it from
shorting. Not sure the legality of bypassing the switch for a flight
though?