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Dancing ammeter and alternator drop outs

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thomas.n.gautier(at)jpl.n
Guest

Posted: Fri Dec 05, 2008 2:12 pm Post subject: Dancing ammeter and alternator drop outs

Bob,



     Our club Arrow IV has recently experienced a spate of alternator and

related electrical system maintenance issues. The symptoms that the club

members complained about centered on alternator drop outs which could often,

if not always, be cured by turning the alternator off and then back on.

There may have been an outright alternator failure of some sort as well. I

haven't followed the maintenance in detail since I haven't, until today,

flown the plane in the last month.



     The upshot of all the maintenance is that first the voltage regulator

and then the alternator were replaced. The symptom reported after voltage

regulator replacement but before alternator replacement was that the

alternator was dropping out every 10 minutes in the last half hour of a

cross country trip. I was the first to fly the plane after the alternator

replacement and I found the system to still be misbehaving.



     In my flight immediately upon starting the engine and switching on the

alternator the alternator ammeter (a load meter, I think) showed 70 amps,

pretty steady, recharging the battery I presume. Then, in less than a minute

the ammeter began swinging from 30A to 70A 2 or 3 times a second. I've read

your dancing ammeter posts so I assumed this was not particularly

troublesome (except that these swings were larger than I had seen before).

Then, after my first turn around the pattern, I noticed that the alternator

had dropped off line. It came back after cycling the alternator switch,

however the ammeter dancing was now as large as 0A to 70A. This behavior

continued for a couple more turns around the pattern, with full stop

landings, as I watched what was going on. I had to reset the alternator

twice more over the span of 20 minutes.



    So, the plane's electrical problems are not solved and I'm trying to

help the owner and his mechanic figure out what is really wrong. I dug some

of your posts about dancing ammeters out of the archive and I'm ready to

show them to the plane's owner. However I'd like to get your opinion as to

whether I'm on the right track. Can the aging wiring problem that causes

dancing ammeters also cause the alternator to frequently drop off line?



Regards,

Nick Gautier

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nuckolls.bob(at)aeroelect
Guest

Posted: Sat Dec 06, 2008 6:48 am Post subject: Dancing ammeter and alternator drop outs

At 04:11 PM 12/5/2008, you wrote:

 	  Quote: 	
		  

<thomas.n.gautier(at)jpl.nasa.gov>



Bob,



      Our club Arrow IV has recently experienced a spate of alternator and

related electrical system maintenance issues. The symptoms that the club

members complained about centered on alternator drop outs which could often,

if not always, be cured by turning the alternator off and then back on.

There may have been an outright alternator failure of some sort as well. I

haven't followed the maintenance in detail since I haven't, until today,

flown the plane in the last month.


	


   By "drop out" do you mean that the alternator shuts down completely?

   Do you get a low voltage warning or does the ammeter go to zero

   and stay there?



 	  Quote: 	
		        The upshot of all the maintenance is that first the voltage regulator

and then the alternator were replaced. The symptom reported after voltage

regulator replacement but before alternator replacement was that the

alternator was dropping out every 10 minutes in the last half hour of a

cross country trip. I was the first to fly the plane after the alternator

replacement and I found the system to still be misbehaving.



      In my flight immediately upon starting the engine and switching on the

alternator the alternator ammeter (a load meter, I think) showed 70 amps,

pretty steady, recharging the battery I presume. Then, in less than a minute

the ammeter began swinging from 30A to 70A 2 or 3 times a second. I've read

your dancing ammeter posts so I assumed this was not particularly

troublesome (except that these swings were larger than I had seen before).

Then, after my first turn around the pattern, I noticed that the alternator

had dropped off line. It came back after cycling the alternator switch,

however the ammeter dancing was now as large as 0A to 70A. This behavior

continued for a couple more turns around the pattern, with full stop

landings, as I watched what was going on. I had to reset the alternator

twice more over the span of 20 minutes.


	


   I'm trying to deduce if you're speaking to an intermittent operation.

   A lack of ability for the alternator to deliver any power at all . . . or

   an unstable condition where the alternator is always developing some

   power but the regulation is unstable.



 	  Quote: 	
		       So, the plane's electrical problems are not solved and I'm trying to

help the owner and his mechanic figure out what is really wrong. I dug some

of your posts about dancing ammeters out of the archive and I'm ready to

show them to the plane's owner. However I'd like to get your opinion as to

whether I'm on the right track. Can the aging wiring problem that causes

dancing ammeters also cause the alternator to frequently drop off line?


	


   You use the words "dancing ammeter". Go to



http://www.matronics.com/searching/ws_script.cgi



   Search the AeroElectric List archive using search string . . .



   dancing & ammeter



   You will unearth a lot of conversation about a phenomenon

   common to older airplanes where the voltage regulator senses

   bus voltage through the same wire that supplies field current.

   This sets up the possibility for a "negative resistance" (read

   oscillation) of voltage regulator stability that can be

   anything from barely noticeable to quite severe.



   It has nothing to do with the alternator or the regulator and

   everything to do with condition of ALL wires, components and

   joints between the bus and the regulator. The 30-year fix is to

   replace ALL these components.



   If you're describing an oscillating voltage condition, then

   the discussions and recommended fixes described in the archives

   are the road to Nirvana. If you're describing an intermittent

   functionality where the alternator output goes to zero and

   stays there for some observable time interval . . . you're

   chasing a loose connection.



   Bob . . .

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thomas.n.gautier(at)jpl.n
Guest

Posted: Sun Dec 07, 2008 7:31 am Post subject: Dancing ammeter and alternator drop outs

Bob,



     Thanks for your reply. I'm sorry I was not more specific.



     The current symptom of the airplane is that the alternator will shut

down and produce no current. The load meter goes to zero and the voltage

drops to the battery voltage, a little over 12v on my flight. Turning the

alternator half of the split master off and then back on restores alternator

output, the load meter goes to 70A briefly and then starts dancing. I

carelessly did not observe the voltage with the alternator working. After

ten or 15 minutes the alternator output will again go to zero. Cycling the

alternator half of the master will again restore the load meter indication.

The 5A alternator field breaker does not pop during this process. I am

unsure how long I left the alternator off line before cycling the split

master.



     I did search the archives for 'dancing & ammeter' and I understand the

issue of excessive resistance in the voltage sense/field current wire. Looks

to me like this plane has that problem. You seem to be saying that the

alternator drop out I describe is not related to the dancing ammeter symptom

but that the drop outs are probably caused by a loose connection. But why

would cycling the alternator half of the master reliably restore operation

if there was a loose connection?



     Are there any more tests you would suggest?



    Thanks much for your attention.



Nick Gautier

You wrote:

Time: 06:48:48 AM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

Subject: Re: Dancing ammeter and alternator drop outs

At 04:11 PM 12/5/2008, you wrote:

 	  Quote: 	
		  <thomas.n.gautier(at)jpl.nasa.gov>



Bob,



      Our club Arrow IV has recently experienced a spate of alternator and

related electrical system maintenance issues. The symptoms that the club

members complained about centered on alternator drop outs which could often,

if not always, be cured by turning the alternator off and then back on.

There may have been an outright alternator failure of some sort as well. I

haven't followed the maintenance in detail since I haven't, until today,

flown the plane in the last month.


	


   By "drop out" do you mean that the alternator shuts down completely?

   Do you get a low voltage warning or does the ammeter go to zero

   and stay there?



 	  Quote: 	
		        The upshot of all the maintenance is that first the voltage regulator

and then the alternator were replaced. The symptom reported after voltage

regulator replacement but before alternator replacement was that the

alternator was dropping out every 10 minutes in the last half hour of a

cross country trip. I was the first to fly the plane after the alternator

replacement and I found the system to still be misbehaving.



      In my flight immediately upon starting the engine and switching on the

alternator the alternator ammeter (a load meter, I think) showed 70 amps,

pretty steady, recharging the battery I presume. Then, in less than a minute

the ammeter began swinging from 30A to 70A 2 or 3 times a second. I've read

your dancing ammeter posts so I assumed this was not particularly

troublesome (except that these swings were larger than I had seen before).

Then, after my first turn around the pattern, I noticed that the alternator

had dropped off line. It came back after cycling the alternator switch,

however the ammeter dancing was now as large as 0A to 70A. This behavior

continued for a couple more turns around the pattern, with full stop

landings, as I watched what was going on. I had to reset the alternator

twice more over the span of 20 minutes.


	


   I'm trying to deduce if you're speaking to an intermittent operation.

   A lack of ability for the alternator to deliver any power at all . . . or

   an unstable condition where the alternator is always developing some

   power but the regulation is unstable.



 	  Quote: 	
		       So, the plane's electrical problems are not solved and I'm trying to

help the owner and his mechanic figure out what is really wrong. I dug some

of your posts about dancing ammeters out of the archive and I'm ready to

show them to the plane's owner. However I'd like to get your opinion as to

whether I'm on the right track. Can the aging wiring problem that causes

dancing ammeters also cause the alternator to frequently drop off line?


	


   You use the words "dancing ammeter". Go to



http://www.matronics.com/searching/ws_script.cgi



   Search the AeroElectric List archive using search string . . .



   dancing & ammeter



   You will unearth a lot of conversation about a phenomenon

   common to older airplanes where the voltage regulator senses

   bus voltage through the same wire that supplies field current.

   This sets up the possibility for a "negative resistance" (read

   oscillation) of voltage regulator stability that can be

   anything from barely noticeable to quite severe.



   It has nothing to do with the alternator or the regulator and

   everything to do with condition of ALL wires, components and

   joints between the bus and the regulator. The 30-year fix is to

   replace ALL these components.



   If you're describing an oscillating voltage condition, then

   the discussions and recommended fixes described in the archives

   are the road to Nirvana. If you're describing an intermittent

   functionality where the alternator output goes to zero and

   stays there for some observable time interval . . . you're

   chasing a loose connection.



   Bob . . .

- 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:

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thomas.n.gautier(at)jpl.n
Guest

Posted: Mon Dec 08, 2008 8:48 am Post subject: Dancing ammeter and alternator drop outs

Bob,



     Thanks. I'll send your comments along to the owner and mechanic and

I'll try to get the switch carcass if its replaced.



Nick Gautier



You Wrote:



Time: 09:47:56 AM PST US

From: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>

Subject: Re: Re: Dancing ammeter and alternator drop

outs



At 09:28 AM 12/7/2008, you wrote:

 	  Quote: 	
		  <thomas.n.gautier(at)jpl.nasa.gov>



Bob,



      Thanks for your reply. I'm sorry I was not more specific.


	


    Not a problem . . .

 	  Quote: 	
		        The current symptom of the airplane is that the alternator will shut

down and produce no current. The load meter goes to zero and the voltage

drops to the battery voltage, a little over 12v on my flight. Turning the

alternator half of the split master off and then back on restores alternator

output, the load meter goes to 70A briefly and then starts dancing. I

carelessly did not observe the voltage with the alternator working. After

ten or 15 minutes the alternator output will again go to zero. Cycling the

alternator half of the master will again restore the load meter indication.

The 5A alternator field breaker does not pop during this process. I am

unsure how long I left the alternator off line before cycling the split

master.


	


    These split-rocker switches are close cousins to the S700 series

    Carling toggle switches offered by B&C and described here:



http://aeroelectric.com/Mfgr_Data/Switches/Carling_G-series.pdf



http://aeroelectric.com/Pictures/Switches/Carling_Cutaway.jpg



http://aeroelectric.com/Pictures/Switches/Split_Rocker_Front.jpg



http://aeroelectric.com/Pictures/Switches/Split_Rocker_Rear.jpg



    I used to have a plastic bag in my desk drawer that contained

    two split-rockers removed from TC aircraft that were plagued

    with some form of alternator recalcitrance . . . teardown inspection

    showed that the contacts on the alternator were badly degraded

    due to combinations of corrosion exacerbated by time, and current

    draw thorough the switch's rising contact resistance. Next

    time I put my hands on them, I'll get them photographed for the

    rogue's gallery of switch failures.

 	  Quote: 	
		        I did search the archives for 'dancing & ammeter' and I understand the

issue of excessive resistance in the voltage sense/field current wire. Looks

to me like this plane has that problem.


	


    It's quite possible . . .

 	  Quote: 	
		    You seem to be saying that the

alternator drop out I describe is not related to the dancing ammeter symptom

but that the drop outs are probably caused by a loose connection. But why

would cycling the alternator half of the master reliably restore operation

if there was a loose connection?


	


    You're very close to answering your own question with

    a high probability of accuracy . . . what gets "wiggled"

    when you cycle the switch?

 	  Quote: 	
		        Are there any more tests you would suggest?


	


    Sure, take a voltmeter along and do the divide/conquer study.

    Connect a test lead at half-way between bus and alternator

    field terminal. See if you can get the problem to repeat.

    If symptom repeats and voltage disappears during alternator

    misbehavior, move test point toward the bus 1/4 of the way

    and test again. If you're feeling really confident about the

    switch, just probe the downstream side of the switch.



    Now, if there's alternator ammeter wiggle when things are

    working "normally", then perhaps you can get the folks to

    do the bus-to-regulator refurbishment cited in the aforementioned

    articles . . . most likely, this will fix both the dancing

    ammeter -AND- the alternator drop out. If you do replace the

    switch for any reason, I'd like to have the carcass.



    Bob . . .

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