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Thread: Electrical Diagonsitic Assistance Needed - Archive Search Fo

  1. #1

    Electrical Diagonsitic Assistance Needed - Archive Search Fo

    >The A&P was away, but his assistant suggested that we remove the
    >alternator and get it tested at an auto shop. I did (as for a Ford
    >pick-up, which mysteriously matched Bob Steward's advice now that I
    >have searched the BAC & MM archives), and it failed. The needle only
    >moved a bit.

    If it failed to charge properly, then its either got bad connections on the
    field (worn brushes), or shorted windings or bad diode(s).

    >My problem is this, none of the former posts that I found mentioned
    >popping a breaker when an alternator went out. Further, Bob Steward's
    >advice to check resistance from the field terminal to ground stated
    >that 4-10 ohms should be obtained. I get 6.

    That is just the field resistance, and not the only failure mode.

    >So, does this really sound like an alternator issue to you? Could the
    >guy at AutoZone have made a mistake with the sey-up and it is OK while
    >the problem lies elsewhere? Have you noticed how suspiciously the
    >guys at the auto shop look at you when all you have to say about a
    >part is Ford pickup, big engine, 60 Amps?

    Well you can tell them it is for a 71 Ford P/U with AC, which IS the actual
    application for the DOFF-10300J.

    Its dead simple. You hook up a ground to the case, a power output lead to
    the big terminal and the field wire to the "F" terminal. Spin alternator
    up and apply voltage to the F terminal. It ought to charge nicely at 55-65
    amps and 17 volts (depends on the way their machine is set up). If it only
    worked "a little", then it has internal problems.

    >If it is a failure, then I need to search for a DOF10300M!

    DOFF-10300 is the base part number, and most of them are "J", not "M" suffix.

    Retest at another shop to confirm your concerns, and then replace if it
    does not work correctly.

    However I am concerned about the breaker popping. An open circuit failure
    in the alternator will cause the ammeter to read zero or a small
    discharge. However the breaker(s) won't pop. There is a 60A main breaker
    and a ~5A alternator field breaker that powers the Voltage
    Regulator. Which one is popping?

    If there is a short in the field wiring or regulator, the 5A breaker may
    pop, and put the alternator off line, however the only thing that can cause
    the 60A breaker to pop is a major short or a weak breaker.

    I'm afraid that the Mechanic's Apprentice (often similar to the Sorcerer's
    Apprentice in that Disney cartoon) may have sent you chasing "alternator"
    problems when you should have done a wee bit more troubleshooting before
    taking the alternator off.

    Bob Steward, A&P IA
    Birmingham, AL




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  2. #2

    Electrical Diagonsitic Assistance Needed - Archive Search Fo

    First Things First - Yes, archives searched as you will see below.

    1.7 hours into a 4 hour cross country today in my 77 C24R, my panel
    scan revealed that the ammeter had changed from a slight charge to a
    slight discharge condition. Scanning further, I discovered that the
    breaker labled "Alternator" had popped.

    Pushing it back in caused a hiss on the radio (which by the way I had
    heard earlier as if someone had pressed a PTT without speaking), then
    the breaker would trip again after 3 seconds. I let things cool down,
    then tried again. This time I noticed that the ammeter went to full
    discharge, so I pulled the breaker myself that time.

    I turned homeward as I tried various combinations of switch and
    breaker settings with no useful effect.

    The A&P was away, but his assistant suggested that we remove the
    alternator and get it tested at an auto shop. I did (as for a Ford
    pick-up, which mysteriously matched Bob Steward's advice now that I
    have searched the BAC & MM archives), and it failed. The needle only
    moved a bit.

    My problem is this, none of the former posts that I found mentioned
    popping a breaker when an alternator went out. Further, Bob Steward's
    advice to check resistance from the field terminal to ground stated
    that 4-10 ohms should be obtained. I get 6.

    So, does this really sound like an alternator issue to you? Could the
    guy at AutoZone have made a mistake with the sey-up and it is OK while
    the problem lies elsewhere? Have you noticed how suspiciously the
    guys at the auto shop look at you when all you have to say about a
    part is Ford pickup, big engine, 60 Amps?

    If it is a failure, then I need to search for a DOF10300M!

    Unfortunately I missed my niece's big day, but so goes life.

    Gerald




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  3. #3

    Electrical Diagonsitic Assistance Needed - Archive Search Fo

    As Bob Steward has pointed out, insufficient diagnostics were done in this case, before pulling the alternator. Bob already covered the alternator identification and testing aspects in his comments, and he questioned what breaker was tripping. Bench testing of this simple alternator should be conclusive. However, there will be a need for additional on-aircraft diagnostics when a known-good alternator is reinstalled.

    It isn't uncommon for an actual alternator failure to trip the alternator field breaker (usually 5A). It is somewhat uncommon for it to trip the main alternator output breaker (usually 50A in your model). However, the most common wear and age-related alternator failure symptom is just low or no output (low charging rate). The C24R came with a transistorized voltage regulator and a separate over-voltage relay. Both were made by Lamar, and I consider both to be notoriously unreliable. Almost any other regulator will outlast these units, no matter who repairs them. The most common failure mode, for both items, is an internal short. This typically spikes the alternator output voltage and trips the alternator field breaker. The second most common failure is an open diode, as the approved parts specs are marginal for the application. If an actual alternator failure creates a field circuit short, it will usually take the Lamar regulator with it. BTW, this system uses a field circuit that is fed from the regulator, and internally grounded in the alternator field circuit (through a brush to a slip ring, through the field winding, out the other slip ring to the second brush, and from there to the case ground). The Delco system uses the opposite approach (the regulator grounds the field). You cannot universally apply alternator and regulator advice unless you know the system type involved. While these are not absolutes, the key aspects are:
    1. If an over-voltage occurs and the field breaker trips, the most likely culprit is the regulator or OV relay.
    2. If a lack of charging occurs but no breakers trip, is usually a bad alternator or faulty connection (usually in the field circuit, such as worn-out brushes). It can also be bad diodes, which will usually add radio noise to the symptoms. Note that an internally shorted field may trip the field breaker, but it can also just result in greatly accelerated brush wear.
    3. If a lack of charging occurs and the main output breaker trips, a serious short circuit is possible. If you are watching, you often see a brief charging surge before the breaker trips.
    4. If a lack of charging occurs and the field circuit breaker trips, it implies a short in the field circuit, either in the regulator, wiring, or alternator.

    Which leads me to a final observation. Continuing to repeatedly reset tripped breakers in flight is an invitation to smoke in the cockpit (or worse). There is usually no harm in one or two reset attempts on the 5A field breaker; nor in one reset of the main breaker, if heavy loads were on when it tripped (and some can be shed). But unless you are trying to overcome a crisis that WILL lead to misfortune unless power is restored, it is unwise to keep taking actions that might well lead to unnecessary misfortune. If you can live with it as-is until you land, that's the best route to take.

    When it comes to replacing the Lamar regulators and OV relays in an alternator application, give Zeftronics/Hazotronics a call, and see what they can offer for your application. If they have one that will work for you, it will usually have on-board diagnostic indicators, and will be nearly bulletproof. http://www.zeftronics.com/
    There is more on this in BAC.

    [Non-text portions of this message have been removed]



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  4. #4

    Electrical Diagonsitic Assistance Needed - Archive Search Fo

    I'm glad that Mike wrote that he will archive this in BAC, as this
    is a GREAT summary. It took me years to learn what he just offered
    in a posting.

    What I want to add is about the resetting of circuit breakers and
    the potential fire hazard. Following the SwissAir 111 in-flight
    fire, the airlines instruct crews to not reset or allow one reset,
    while in flight. This should also be the case for us little guys.
    Continued shorting will destroy adjacent wiring and you can lose
    MORE than what is already gone after the initial short. The stock
    wiring (at least in our '74 Sport) is largely PVC insulation, which
    won't snuff flame, especially with 30+ years of oils and
    contaminates. The black smoke is also extremely bad for your staying
    conscious.

    Further, many airplanes have the wiring tucked against the hidden
    side of the sidewall panels, which in our Sport is a polystyrene
    plastic. We took a piece and lit it with a match - it burned
    vigorously. Fortunately, a lot of these older airplanes have new
    interiors and the flame-resistant/stopping sidewall fabric is put
    over sheetmetal, eliminating this hazard.

    Bob
    A&P, Aero Eng

    --- In musketeermail@yahoogroups.com, "Mike Rellihan"
    <rellihan@r...> wrote:
    > As Bob Steward has pointed out, insufficient diagnostics were done
    in this case, before pulling the alternator. Bob already covered
    the alternator identification and testing aspects in his comments,
    and he questioned what breaker was tripping. Bench testing of this
    simple alternator should be conclusive. However, there will be a
    need for additional on-aircraft diagnostics when a known-good
    alternator is reinstalled.
    >
    > It isn't uncommon for an actual alternator failure to trip the
    alternator field breaker (usually 5A). It is somewhat uncommon for
    it to trip the main alternator output breaker (usually 50A in your
    model). However, the most common wear and age-related alternator
    failure symptom is just low or no output (low charging rate). The
    C24R came with a transistorized voltage regulator and a separate
    over-voltage relay. Both were made by Lamar, and I consider both to
    be notoriously unreliable. Almost any other regulator will outlast
    these units, no matter who repairs them. The most common failure
    mode, for both items, is an internal short. This typically spikes
    the alternator output voltage and trips the alternator field
    breaker. The second most common failure is an open diode, as the
    approved parts specs are marginal for the application. If an
    actual alternator failure creates a field circuit short, it will
    usually take the Lamar regulator with it. BTW, this system uses a
    field circuit that is fed from the regulator, and internally
    grounded in the alternator field circuit (through a brush to a slip
    ring, through the field winding, out the other slip ring to the
    second brush, and from there to the case ground). The Delco system
    uses the opposite approach (the regulator grounds the field). You
    cannot universally apply alternator and regulator advice unless you
    know the system type involved. While these are not absolutes, the
    key aspects are:
    > 1. If an over-voltage occurs and the field breaker trips, the
    most likely culprit is the regulator or OV relay.
    > 2. If a lack of charging occurs but no breakers trip, is usually
    a bad alternator or faulty connection (usually in the field circuit,
    such as worn-out brushes). It can also be bad diodes, which will
    usually add radio noise to the symptoms. Note that an internally
    shorted field may trip the field breaker, but it can also just
    result in greatly accelerated brush wear.
    > 3. If a lack of charging occurs and the main output breaker
    trips, a serious short circuit is possible. If you are watching,
    you often see a brief charging surge before the breaker trips.
    > 4. If a lack of charging occurs and the field circuit breaker
    trips, it implies a short in the field circuit, either in the
    regulator, wiring, or alternator.
    >
    > Which leads me to a final observation. Continuing to repeatedly
    reset tripped breakers in flight is an invitation to smoke in the
    cockpit (or worse). There is usually no harm in one or two reset
    attempts on the 5A field breaker; nor in one reset of the main
    breaker, if heavy loads were on when it tripped (and some can be
    shed). But unless you are trying to overcome a crisis that WILL
    lead to misfortune unless power is restored, it is unwise to keep
    taking actions that might well lead to unnecessary misfortune. If
    you can live with it as-is until you land, that's the best route to
    take.
    >
    > When it comes to replacing the Lamar regulators and OV relays in
    an alternator application, give Zeftronics/Hazotronics a call, and
    see what they can offer for your application. If they have one that
    will work for you, it will usually have on-board diagnostic
    indicators, and will be nearly bulletproof.
    http://www.zeftronics.com/
    > There is more on this in BAC.
    >
    > [Non-text portions of this message have been removed]




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