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Thread: The Eternal Alternator Choice Topic

  1. #91
    Gilbert Pierce's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    Quote Originally Posted by Homer Landreth View Post
    Alternator Whine is an AC frequency escape. The only source of AC is internal within the alternator at what are called "slip rings". Alternator Whine is 80 percent or more caused by dirty or improperly installed or worn slip rings. The suggestion to get a new alternator is problematically and statistically valid over using capacitors.
    Homer I don't think so. You need to go back and study your alternator theory and operation.

    The slip rings get D.C. from the diode trio, a three phase rectifier used only to provide D.C. internally. That D.C. then goes to the voltage regulator and the rotor coil via the brushes to generate the controllable moving magnetic field.
    The only AC in an alternator is in the stator windings which are terminated at the main rectifier. If you have an AC whine in an alternator it is caused by a bad diode in the rectifier.

    The Stator is a fixed three phase winding, usually a delta, some use a wye. The diode trio is a thee phase half wave rectifier; three diodes in one capsule. The main rectifier is a Three phase full wave rectifier; six diodes pressed into a heat sink.
    Last edited by Gilbert Pierce; 10-07-2017 at 01:56 PM.

  2. #92
    Homer Landreth's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    Quote Originally Posted by Gilbert Pierce View Post
    Homer I don't think so. You need to go back and study your alternator theory and operation.

    The slip rings get D.C. from the diode trio, a three phase rectifier used only to provide D.C. internally. That D.C. then goes to the voltage regulator and the rotor coil via the brushes to generate the controllable moving magnetic field.
    The only AC in an alternator is in the stator windings which are terminated at the main rectifier. If you have an AC whine in an alternator it is caused by a bad diode in the rectifier.

    The Stator is a fixed three phase winding, usually a delta, some use a wye. The diode trio is a thee phase half wave rectifier; three diodes in one capsule. The main rectifier is a Three phase full wave rectifier; six diodes pressed into a heat sink.
    That is true and is a potential. However bad slip rings can introduce an AC component into the DC it is supposed to be passing to the rotating components. It is not as simple as only one thing that can cause whine, HOWEVER if Gilbert wants to be "right" I will yield to his theory. Bottom line is that the first step in the trouble shooting flow chart is the question "Did you screw around with it ?" If you did, then maybe that should be the first place to start looking.

  3. #93
    Gilbert Pierce's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    Quote Originally Posted by Homer Landreth View Post
    Alternator Whine is an AC frequency escape. The only source of AC is internal within the alternator at what are called "slip rings". Alternator Whine is 80 percent or more caused by dirty or improperly installed or worn slip rings. The suggestion to get a new alternator is problematically and statistically valid over using capacitors.
    An interesting dynamic here. Homer is always right.
    My experience is dirty slip rings cause an arc which is heared as a cracking sound.
    A bad diode causes incomplete rectification of the AC Generated in the stator windings. AC is heard as a variable frequency whine.
    Last edited by Gilbert Pierce; 10-07-2017 at 04:33 PM.

  4. #94
    Homer Landreth's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    I only claimed 80 percent.

  5. #95
    Gilbert Pierce's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    Re-clocking an alternator as Mr Perkins did is not unusual. Some vendors only sell them configured for the most popular installations; same alternator different part-number. If the alternator requires re-clocking it is almost always necessary to separate the rotor end from the stator end and this always exposes the brushes and slip rings.
    I re-clocked one just yesterday and tried to it without separating the halves as that requires resetting the brushes and pinning them into the brush holder. Didn't work. Had to separate the halves, remove the stator to get to the brush holder.
    Some re-builders and OEM manufactures include instructions in the box in case you have to re-clock it.

  6. #96
    Administrator Steve Pierce's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    I had an alternator go out on a customer's Saratoga once. No one had one. Vendor told me it was just a reclocked version of a very common alternator which was $600. The reclocked version that I needed was $2500.

  7. #97
    JPerkins's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    Cleaned mounting points and nothing changed. Tried a jumper wire (car jumper cables) from the body of the alternator straight to battery negative terminal, no change. Did same with radio housing, no change.
    Went and played in the foothills and came to the realization that the sound is almost digital. Then it dawned on me that the regulator most likely uses pulse width modulation (looked but could not find any information on this alternator to confirm). And if it was a low dollar rebuild, it could likely have a cheaply made voltage regulator that puts out noise like the cheap phone chargers. After all it was listed for a reefer engine, not like they have to worry about emf noise with that application.

    I'm undecided wether to buy another alternator from a reputable vendor. Or try and allocate a voltage regulator (with my reputable vendor does not carry).
    Either way with this fall weather and winter setting in, I'll be lucky to get ten hours of flying in. So I will just put up with the noise and deal with this issue next annual in the spring.



    Sent from my SM-G930V using Tapatalk

  8. #98
    Gilbert Pierce's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    J, Voltage regulators use off/on switching to control output voltage via the rotor coil current. Some alternators, most notably Delco use a capacitor across the VR inside the alternator case to quiet it down.

  9. #99
    51-pa22's Avatar
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    Default Re: The Eternal Alternator Choice Topic

    Didnt plane power offer a 40A denso type alternator and use their external regulator, similar to B&C's 40A setup?

  10. #100
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    Default Re: The Eternal Alternator Choice Topic

    Didn't find a 40 amp stc for the tri pacers and pacers. That's why I went field approval. 70 amp just seemed overkill and unnecessary weight for a vfr plane.

    Or maybe it was the price...Don't remember know.
    Last edited by JPerkins; 10-09-2017 at 11:21 PM.

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