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Seeking alternator troubleshooting advice

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon Sep 03, 2012 6:37 pm Post subject: Seeking alternator troubleshooting advice

At 06:01 PM 9/3/2012, you wrote:

On the way home from OSH last month my RV6A started to indicate on 

the voltage meter readings fluctuating from 14+ to 12.4 or 

so.  During the last two legs of the flight lasting a total of about 

4 hours with all my avionics and usual accessories activated the 

voltage never dropped below 12.2..



	The voltage cannot exceed about 12.8 without the

	alternator functioning. The voltage cannot fall

	lower than what the battery will deliver given

	present loads and the battery's state of charge.



	Had your airplane been fitted with a low votlage

	warning light, it would have notified you of the

	fact that the alternator was not producing power.



A week or so after I returned to my home airport I took the plane 

around the pattern to check the voltages again.  During taxi to the 

runway the voltage would indicate 12.2-4.



	Which meant that your alternator speed was too low

	to produce regulated power at ground maneuvering

	RPMs (unlikely in the typical Lycoming installation)

	-OR- the alternator was not operating. Again, a

	low voltage warning light would be agitating for

	attention.



After I pushed the throttle in for takeoff the voltage went to 14.2 

and stayed there while flying at 75% power for 20 minutes or so.  I 

thought the problem I had previously experienced had resolved 

itself.  However, as soon as a reduced the throttle to descend for 

landing the voltage once again dropped to the 12's and fluctuated up and down.



	The alternator is suffering intermittent difficulties

	that prevents it from functioning as expected.



I am not the builder (second owner) so I am not sure if the 

alternator is internally or externally regulated.  There are no 

manufacturer markings on the alternator and I do not see anything 

that looks like an external voltage regulator on the firewall.  The 

back of the alternator has one large cable and three small 

wires.  Two of the wires are clipped to the back of the alternator on 

thin posts at 90 degrees to each other and the third wire is attached 

the case of the alternator in what looks like a ground wire.



	Sounds like the typical automotive, internally regulated

	alternator.



The battery is less than a year old and indicates 12.4.  The plane 

starts in a couple of turns.



	Battery good, alternator or alternator

	wiring bad.



I have a spare alternator that came with the plane that is a 

Mitsubishi car alternator. I am wondering if I should just change out 

the alternator to try to solve the problem or are there other ways to 

determine the cause of the problem.



	The assuming no intermittent commands to the alternator

	causing it to be turned on and off under vibration,

	then the alternator is probably needing attention.

	You can do an experiment to install a jumper wire from

	the alternator B-terminal to the IGN terminal and see

	if the intermittent behavior goes away. Alternatively,

	you can change out the alternator to see if that

	fixes the problem. The earlier experiment is

	the easiest.



	Is your spare alternator identical to the one that's

	installed?



	Bob . . .

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Reddogally(at)aol.com
Guest

Posted: Mon Sep 03, 2012 7:43 pm Post subject: Seeking alternator troubleshooting advice

The spare alternator looks to be identical to the faulty one except the  spare one has a Mitsubishi logo on the case that I do not see on the installed  one.  The attachment mounts and wiring locations look to be the same and in  the same locations.

  

 Thanks for the advice.  I will give it a try tomorrow.

  

 Doug

  

  In a message dated 9/3/2012 7:37:59 P.M. Pacific Daylight Time,  nuckolls.bob(at)aeroelectric.com writes:

  	  Quote: 	
		  -->    AeroElectric-List message posted by: "Robert L. Nuckolls, III"    <nuckolls.bob(at)aeroelectric.com>



At 06:01 PM 9/3/2012, you    wrote:

On the way home from OSH last month my RV6A started to indicate on    

the voltage meter readings fluctuating from 14+ to 12.4 or 

so.     During the last two legs of the flight lasting a total of about 

4 hours    with all my avionics and usual accessories activated the 

voltage never    dropped below 12.2..



    The voltage cannot exceed about 12.8    without the

    alternator functioning. The voltage cannot    fall

    lower than what the battery will deliver given

       present loads and the battery's state of charge.



       Had your airplane been fitted with a low votlage

    warning    light, it would have notified you of the

    fact that the    alternator was not producing power.



A week or so after I returned to my    home airport I took the plane 

around the pattern to check the voltages    again.  During taxi to the 

runway the voltage would indicate    12.2-4.



    Which meant that your alternator speed was too    low

    to produce regulated power at ground    maneuvering

    RPMs (unlikely in the typical Lycoming    installation)

    -OR- the alternator was not operating. Again,    a

    low voltage warning light would be agitating for

       attention.



After I pushed the throttle in for takeoff the    voltage went to 14.2 

and stayed there while flying at 75% power for 20    minutes or so.  I 

thought the problem I had previously experienced    had resolved 

itself.  However, as soon as a reduced the throttle to    descend for 

landing the voltage once again dropped to the 12's and    fluctuated up and down.



    The alternator is suffering    intermittent difficulties

    that prevents it from functioning    as expected.



I am not the builder (second owner) so I am not sure if    the 

alternator is internally or externally regulated.  There are no    

manufacturer markings on the alternator and I do not see anything 

that    looks like an external voltage regulator on the firewall.  The 

back    of the alternator has one large cable and three small 

wires.  Two of    the wires are clipped to the back of the alternator on 

thin posts at 90    degrees to each other and the third wire is attached 

the case of the    alternator in what looks like a ground wire.



    Sounds like    the typical automotive, internally regulated

       alternator.



The battery is less than a year old and indicates    12.4.  The plane 

starts in a couple of turns.



       Battery good, alternator or alternator

    wiring bad.



I    have a spare alternator that came with the plane that is a 

Mitsubishi car    alternator. I am wondering if I should just change out 

the alternator to    try to solve the problem or are there other ways to 

determine the cause of    the problem.



    The assuming no intermittent commands to the    alternator

    causing it to be turned on and off under    vibration,

    then the alternator is probably needing    attention.

    You can do an experiment to install a jumper wire    from

    the alternator B-terminal to the IGN terminal and    see

    if the intermittent behavior goes away.    Alternatively,

    you can change out the alternator to see if    that

    fixes the problem. The earlier experiment is

       the easiest.



    Is your spare alternator identical to    the one that's

    installed?



    Bob . .  = Use  ilities  ay                 - MATRONICS WEB FORUMS               - List Contribution Web Site  p;                             



	


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