Today's Message Index:
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1. 07:31 AM - Re: Dancing ammeter and alternator drop outs (Gautier, Thomas N)
2. 09:44 AM - Re: Z-11 Questions (grjtucson)
3. 09:47 AM - Re: Re: Dancing ammeter and alternator drop outs (Robert L. Nuckolls, III)
4. 09:58 AM - Re: Re: Z-11 Questions (Robert L. Nuckolls, III)
Message 1
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| Subject: | Re: 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@aeroelectric.com>
Subject: Re: AeroElectric-List: Dancing ammeter and alternator drop outs
At 04:11 PM 12/5/2008, you wrote:
><thomas.n.gautier@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?
> 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.
> 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 . . .
Message 2
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| Subject: | Re: Z-11 Questions |
Bob,
I'll wire per Z-11 on the bus feeds, thanks for the lesson and illumination.
I am, however, going to wire per E-Mag Air on the mags. For the power feeds, E-Mag
calls for a breaker for the E-Mag and a switch and breaker for the P-Mag,
optionally combining the switch and breaker. I'm just going to use breakers for
both, pulling the P-Mag's when I test it's generator. I prefer the simplicity
of a SPST switch consistently used for both, and should I ever switch to standard
mags, I just delete my panel breakers.
I will feed the breakers from the terminal of the E-bus, not through a fuse.
BTW, the present revision M of Z-13/8 has the P-Mag generator unable to be tested
(open P-Lead and no power) short of powering down the Main bus. I'd think having
the P-Mag get a 3 pos. switch as you had on Rev L would be superior. The
P-Mag would then be Off-On-Bat and the E-Mag would be Off-Bat-On, and you could
feed both from the Battery Bus.
Also, for what it's worth, E-Mag Air does call for 18AWG feeders and grounds, contrary
to the Z diagrams.
Thanks for doing what you do :)
George
--------
George Jenson -
Tucson, AZ - RV-7 Standard Build
Empennage Completed 1/06
Wings Completed 11/06
Fuselage in Progress
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=218027#218027
Message 3
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| Subject: | Re: Dancing ammeter and alternator drop outs |
At 09:28 AM 12/7/2008, you wrote:
><thomas.n.gautier@jpl.nasa.gov>
>
>Bob,
>
> Thanks for your reply. I'm sorry I was not more specific.
Not a problem . . .
> 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.
> 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 . . .
> 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?
> 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 . . .
Message 4
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| Subject: | Re: Z-11 Questions |
At 11:42 AM 12/7/2008, you wrote:
>
>Bob,
>
>I'll wire per Z-11 on the bus feeds, thanks for the lesson and illumination.
>
>I am, however, going to wire per E-Mag Air on the mags. For the
>power feeds, E-Mag calls for a breaker for the E-Mag and a switch
>and breaker for the P-Mag, optionally combining the switch and
>breaker. I'm just going to use breakers for both, pulling the
>P-Mag's when I test it's generator. I prefer the simplicity of a
>SPST switch consistently used for both, and should I ever switch to
>standard mags, I just delete my panel breakers.
>
>I will feed the breakers from the terminal of the E-bus, not through a fuse.
>
>BTW, the present revision M of Z-13/8 has the P-Mag generator unable
>to be tested (open P-Lead and no power) short of powering down the
>Main bus. I'd think having the P-Mag get a 3 pos. switch as you had
>on Rev L would be superior. The P-Mag would then be Off-On-Bat and
>the E-Mag would be Off-Bat-On, and you could feed both from the Battery Bus.
Given that there are two ignition systems with a high
degree of reliability . . . either one of which runs
the engine just fine . . . Emagair told me that there
was very little to be gained by frequent testing of
the E-Mag's self supporting capabilities. They suggested
a couple of times a year. This is easy to do at the same
time you deliberately drop the main bus to do battery-only
endurance verifications or what-ever. The point is that
the system wired as shown CAN be tested by the pilot either
in pre-flight or during flight with the controls configured
as shown.
As shown, one achieves automatic load-shedding of the
E-mag during battery-only ops because IT IS fed from
the main bus.
>Also, for what it's worth, E-Mag Air does call for 18AWG feeders and
>grounds, contrary to the Z diagrams.
Yeah, not necessary from the perspective of operating physics.
It's a mechanical robustness thing.
>Thanks for doing what you do :)
My pleasure sir. I'm pleased that you receive good
value from the effort.
Bob . . .
----------------------------------------)
( . . . a long habit of not thinking )
( a thing wrong, gives it a superficial )
( appearance of being right . . . )
( )
( -Thomas Paine 1776- )
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