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pjc
Joined: 13 Jan 2021
Posts: 7
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 Posted: Wed Jan 13, 2021 8:06 pm Post subject: Alternator rectifier bad? |
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I have an automotive alternator (14184, external “ford” regulator) that has given good service in my RV6. Recently I have noticed fluctuating voltage displayed (digitally) on the USB adapter plugged into a 12V power socket (cigarette lighter style).
Investigating further I see about 2V (RMS) on the bus with my cheapie multimeter when the alternator is running — and measure 14V (fluctuating +2/-0.5) with the meter on DC. I imagine this isn’t doing any good for my Odyssey PC680.
I’m thinking I have a blown diode in the rectifier. Any chance the regulator could be to blame? Any further diagnostics called for before buying a replacement (rebuilt) alternator at the auto parts place ($35) ? Any place to find a replacement rectifier to install in the otherwise still functioning alternator?
As to causes, I am guilty of powering the field on and off a couple of times while the engine was running. This was in effort to diagnose a headphone noise (probably originating from the electro-mechanical regulator switching). I have subsequently been told powering the field on/off while running is a “a bad idea”.
All suggestions welcome.
Peter
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nuckolls.bob(at)aeroelect
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| Posted: Thu Jan 14, 2021 8:13 am Post subject: Alternator rectifier bad? |
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At 10:06 PM 1/13/2021, you wrote:
| Quote: | --> AeroElectric-List message posted by: "pjc" <peter_campo(at)yahoo.com>
I have an automotive alternator (14184, external ford regulator) that has
given good service in my RV6. Recently I have noticed fluctuating voltage
displayed (digitally) on the USB adapter plugged into a 12V power socket
(cigarette lighter style). |
Fluctuating voltage from an alternator is almost
never caused by a failure in the power-output
components (stator wiring and rectifier); it's
almost always caused by some anomaly in the
excitation/regulation side of the house. Regulator,
field supply power path, brushes, etc.
| Quote: | Investigating further I see about 2V (RMS) on the bus with my cheapie
nultimeter when the alternator is running and measure 14V (fluctuating
+2/-0.5) with the meter on DC. |
The output from an alternator is trashy. 3-phase, rectified
power has a built-in peak to peak ripple on the order of
13%. So a 14vdc machine can be expected to come with ~2
volts peak-to-peak ripple. There are test tools intended to
diagnose an abnormal increase in this value as a result
of rectifier failure. An open or shorted diode in a
rectifier will produce a marked increase in ripple
voltage.
Multimeters have varying ability to quantify this
voltage. There's pk-pk, average, rms, etc. Then
there are vagaries in the AC to DC conversion
techniques that the meter ultimately tries to
interpret and display. Some are better at it than
others but unless you have a BENCHMARK ac voltage
reading for a known good alternator, interpreting
the readings you've observed is problematic.
| Quote: | | I imagine this isn’t doing any good for my Odyssey PC680. |
The battery couldn't care less.
| Quote: | | I’m thinking I have a blown diode in the rectifier. |
Unlikely.
| Quote: | Any chance the regulator could be to blame? Any further diagnostics
called for before buying a replacement (rebuilt) alternator at the
auto parts place ($35) ? Any place to find a replacement rectifier
to install in the otherwise still functioning alternator? |
You bet! "Ford" regulators (an those with similar
architecture) are 'hyper sensitive' to increases
in resistance in the field-supply/voltage-sense
pathway.
See the narrative in this document
http://www.aeroelectric.com/articles/Alternators/Know_Your_Charging_System.pdf
That starts on page 8 under, "Battery Master Switch and Battery
Master Relay"
This phenomenon described has often been called
"the galloping/dancing ammeter syndrome". In your case,
it may be the "galloping voltmeter syndrome".
Given the age of your airplane and the 'ford'
regulator, there's a high probability that
your difficulty has roots in this same cause.
(do a Google on "dancing ammeter" and "galloping
ammeter" for a look back in time for this
condition.
Start by fabricating a jumper wire to run
from your regulator A and B terminals directly
to the alternator B terminal thus bypassing ALL
at-risk wiring. Fire the engine up and check
voltage NOTE: THE ALTERNATOR COMES ON LINE
IMMEDIATELY AS FOR AS LONG AS THE ENGINE IS
RUNNING.
If the voltage becomes stable, then consider
renewing ALL components between the bus and
the regulator A and B terminals. Replacing
one item might 'fix' the problem but renewing
all the components comes closer to effecting
a fix good for another 10 years.
To rule out a regulator failure, you can
use a known good regulator to fabricate
the test-tool shown and wire it to the back
of your alternator for a test fun.
This is a problem that has plagued a constellation
of older, single engine aircraft. We've had lengthy
discussions on the List and elsewhere on the 'net.
| Quote: | | As to causes, I am guilty of powering the field on and off a couple of times while the engine was running. This was in effort to diagnose a headphone noise (probably originating from the electro-mechanical regulator switching). I have subsequently been told powering the field on/off while running is a “a bad idea”. |
Contrary to popular myths, that has no deleterious
effect on the system or its components.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?"
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pjc
Joined: 13 Jan 2021
Posts: 7
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| Posted: Thu Jan 14, 2021 8:48 am Post subject: Re: Alternator rectifier bad? |
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Bob,
Thanks for the informative and comprehensive response.
I have enjoyed the “dancing ammeter” (but without observing the voltage fluctuations) for as long as I have been operating this a/c. I assumed it was normal for the old style regulators — especially as I have a relatively high current draw Wheelen strobe power unit charging/discharging periodically.
I have work to do, and will report back!
Peter
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pjc
Joined: 13 Jan 2021
Posts: 7
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| Posted: Mon Feb 01, 2021 1:52 pm Post subject: Re: Alternator rectifier bad? |
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| nuckolls.bob(at)aeroelect wrote: | At 10:06 PM 1/13/2021, you wrote:
| Quote: | --> AeroElectric-List message posted by: "pjc" <peter_campo>
I have an automotive alternator (14184, external ford� regulator) that has
given good service in my RV6. Recently I have noticed fluctuating voltage
displayed (digitally) on the USB adapter plugged into a 12V power socket
(cigarette lighter style). |
Fluctuating voltage from an alternator is almost
never caused by a failure in the power-output
components (stator wiring and rectifier); it's
almost always caused by some anomaly in the
excitation/regulation side of the house. Regulator,
field supply power path, brushes, etc.
| Quote: | Investigating further I see about 2V (RMS) on the bus with my cheapie
nultimeter when the alternator is running and measure 14V (fluctuating
+2/-0.5) with the meter on DC. |
The output from an alternator is trashy. 3-phase, rectified
power has a built-in peak to peak ripple on the order of
13%. So a 14vdc machine can be expected to come with ~2
volts peak-to-peak ripple. There are test tools intended to
diagnose an abnormal increase in this value as a result
of rectifier failure. An open or shorted diode in a
rectifier will produce a marked increase in ripple
voltage.
Multimeters have varying ability to quantify this
voltage. There's pk-pk, average, rms, etc. Then
there are vagaries in the AC to DC conversion
techniques that the meter ultimately tries to
interpret and display. Some are better at it than
others but unless you have a BENCHMARK ac voltage
reading for a known good alternator, interpreting
the readings you've observed is problematic.
| Quote: | | I imagine this isn’t doing any good for my Odyssey PC680. |
The battery couldn't care less.
| Quote: | | I’m thinking I have a blown diode in the rectifier. |
Unlikely.
| Quote: | Any chance the regulator could be to blame? Any further diagnostics
called for before buying a replacement (rebuilt) alternator at the
auto parts place ($35) ? Any place to find a replacement rectifier
to install in the otherwise still functioning alternator? |
You bet! "Ford" regulators (an those with similar
architecture) are 'hyper sensitive' to increases
in resistance in the field-supply/voltage-sense
pathway.
See the narrative in this document
http://www.aeroelectric.com/articles/Alternators/Know_Your_Charging_System.pdf
That starts on page 8 under, "Battery Master Switch and Battery
Master Relay"
This phenomenon described has often been called
"the galloping/dancing ammeter syndrome". In your case,
it may be the "galloping voltmeter syndrome".
Given the age of your airplane and the 'ford'
regulator, there's a high probability that
your difficulty has roots in this same cause.
(do a Google on "dancing ammeter" and "galloping
ammeter" for a look back in time for this
condition.
Start by fabricating a jumper wire to run
from your regulator A and B terminals directly
to the alternator B terminal thus bypassing ALL
at-risk wiring. Fire the engine up and check
voltage NOTE: THE ALTERNATOR COMES ON LINE
IMMEDIATELY AS FOR AS LONG AS THE ENGINE IS
RUNNING.
If the voltage becomes stable, then consider
renewing ALL components between the bus and
the regulator A and B terminals. Replacing
one item might 'fix' the problem but renewing
all the components comes closer to effecting
a fix good for another 10 years.
To rule out a regulator failure, you can
use a known good regulator to fabricate
the test-tool shown and wire it to the back
of your alternator for a test fun.
This is a problem that has plagued a constellation
of older, single engine aircraft. We've had lengthy
discussions on the List and elsewhere on the 'net.
| Quote: | | As to causes, I am guilty of powering the field on and off a couple of times while the engine was running. This was in effort to diagnose a headphone noise (probably originating from the electro-mechanical regulator switching). I have subsequently been told powering the field on/off while running is a “a bad idea”. |
Contrary to popular myths, that has no deleterious
effect on the system or its components.
Bob . . .
Un impeachable logic: George Carlin asked, "If black boxes
survive crashes, why don't they make the whole airplane
out of that stuff?" |
Follow-up:
1). No discrepancies (high resistances) found at Field switch or fuse (though AGC fuse and holder contacts cleaned).
2). No discrepancies at the alternator field and B connections or with the capacitor (condenser) mounted there.
3). Little improvement with further flight time (resulting in higher battery SOC) - this behavior started after a period of no use during annual inspection.
4). Significant improvement from unplugging and reseating the connector at the voltage regulator. Next time the cowl is off I will perform a more comprehensive contact cleaning (tough to do properly through the oil door).
So now I am back to a simple dancing ammeter (with regular period between 1 and 2 Hz) that has been the norm for several years. The “AC component” as measured with my cheapie Digital voltmeter is under 0.5V and my panel lights are no-longer flickering.
I’m chalking this one up to a poor connection at the voltage regulator and returning the replacement alternator.
Thanks very much for the lessons !!
Peter
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
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